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CampylobacterJohn Moore, Deborah Corcoran, James Dooley, Séamus Fanning, Brigid

Lucey, Motoo Matsuda, David Mcdowell, Francis Mégraud, B. Cherie Millar,Rebecca O’Mahony, et al.

To cite this version:John Moore, Deborah Corcoran, James Dooley, Séamus Fanning, Brigid Lucey, et al.. Campylobac-ter. Veterinary Research, BioMed Central, 2005, 36 (3), pp.351-382. �10.1051/vetres:2005012�. �hal-00902984�

https://hal.archives-ouvertes.fr/hal-00902984

https://hal.archives-ouvertes.fr

351Vet. Res. 36 (2005) 351–382© INRA, EDP Sciences, 2005DOI: 10.1051/vetres:2005012

Review article

Campylobacter

John E. MOOREa*, Deborah CORCORANb, James S.G. DOOLEYc, Séamus FANNINGd, Brigid LUCEYe, Motoo MATSUDAf,

David A. MCDOWELLg, Francis MÉGRAUDh, B. Cherie MILLARa, Rebecca O’MAHONYd, Lisa O’RIORDANa, Michele O’ROURKEd, Juluri R. RAOi, Paul J. ROONEYa, Andrew SAILSj, Paul WHYTEd

a Northern Ireland Public Health Laboratory, Department of Bacteriology, Belfast City Hospital, Belfast BT9 7AD, Northern Ireland, United Kingdom

b Molecular Diagnostics Unit, Cork Institute of Technology, Bishopstown, Cork, Irelandc School of Biomedical Sciences, University of Ulster, Coleraine, Co. Londonderry, BT52 1SA,

Northern Ireland, United Kingdomd Centre for Food Safety, Faculties of Agriculture, Medicine & Veterinary Medicine,

University College, Belfield, Dublin 4, Irelande Department of Medical Microbiology, University Hospital, Wilton, Cork, Ireland

f Laboratory of Molecular Biology, School of Environmental Health Sciences, Azabu University, Sagamihara, 229-8501, Japan

g Department of Food Studies, University of Ulster, Jordanstown, Newtownabbey, Co. Antrim, Northern Ireland, United Kingdom

h Laboratoire de Bactériologie, CHU Pellegrin, Place Amélie Raba-Léon, 33076 Bordeaux, Francei Department of Applied Plant Science, Queen’s University, The Agriculture and Food Science Centre,

Newforge Lane, Belfast, BT9 5PX, Northern Ireland, United Kingdomj Health Protection Agency, Institute of Pathology, Newcastle General Hospital,

Newcastle upon tyne NE4 6BE, United Kingdom

(Received 6 December 2004; accepted 1 February 2005)

Abstract – Species within the genus, Campylobacter, have emerged over the last three decades assignificant clinical pathogens, particularly of human public health concern, where the majority ofacute bacterial enteritis in the Western world is due to these organisms. Of particular concern arethe species, C. jejuni and C. coli, which are responsible for most of these gastrointestinal-relatedinfections. Although these organisms have already emerged as causative agents of zoonoses, severalaspects of their epidemiology and pathophysiology are only beginning to emerge. Trends inincreasing antibiotic resistance are beginning to emerge with oral antibiotics, which may be the drugof choice for when it is necessary to intervene chemotherapeutically. This review wishes to examine(i) emerging clinical aspects of the disease, such as Guillain Barré syndrome (GBS), (ii) theassociation between these organisms and poultry as a natural host, (iii) environmental aspects ofCampylobacter epidemiology, (iv) the emergence of atypical campylobacters (v) emerging trendsin antibiotic resistance, (vi) adoption of modern methods for the detection of campylobacters.

epidemiology / poultry / PCR / zoonosis / antibiotic resistance

* Corresponding author: [email protected]

352 J.E. Moore et al.

Table of contents

1. Introduction ......................................................................................................................................3522. Historical emergence of Campylobacter ..........................................................................................3523. Clinical aspects of Campylobacter infections ..................................................................................353

3.1. Enteric infection.......................................................................................................................3533.2. Systemic infection....................................................................................................................3543.3. Post-infectious manifestations .................................................................................................354

4. Human epidemiology and foods of animal origin ............................................................................3554.1. Campylobacters and poultry ....................................................................................................3554.2. Campylobacters and other food animals..................................................................................3564.3. Control in foods of animal origin ............................................................................................356

5. Environmental campylobacters ........................................................................................................3575.1. Water........................................................................................................................................3575.2. Sewage and water treatment plants..........................................................................................3575.3. Farms .......................................................................................................................................3585.4. Food related environments.......................................................................................................359

6. Atypical campylobacters ..................................................................................................................3607. Antibiotic resistance ........................................................................................................................362

7.1. Antimicrobial susceptibility testing in Campylobacter spp.....................................................3637.2. Surveillance of antimicrobial resistance in Campylobacter spp..............................................3647.3. Genetic mechanisms associated with antimicrobial resistance in Campylobacter spp. ..........3657.4. Gene cassettes and class 1 integrons in Campylobacter spp. ..................................................3687.5. MDR-mediated by antimicrobial efflux systems.....................................................................369

8. Campylobacter detection..................................................................................................................3709. Conclusions ......................................................................................................................................373

1. INTRODUCTION

Campylobacter jejuni is a major cause offoodborne illness causing human acute bac-terial enteritis worldwide [8, 164]. Overallthe high incidence of clinical disease asso-ciated with this organism, its low infectivedose in humans [137], and its potentiallyserious sequelae, confirms its importanceas a significant public health hazard [8,164].

Numbers of infections have declinedslightly in some parts of the world duringrecent years, but the overall disease burdenis still significant, thus there remains anurgent need to better understand how thisdisease is transmitted into and within thehuman food chain. Such challenges areincreased by the observation that an increas-ing number of Campylobacter isolates fromhumans and the human food chain exhibitantibiotic resistance and that antimicrobial-

resistant Campylobacter strains cause moreprolonged or more severe illness than doantimicrobial-susceptible strains.

2. HISTORICAL EMERGENCE OF CAMPYLOBACTER

Campylobacter spp. have long beenassociated with the cause of veterinary dis-eases, such as diarrhoea in cattle, and septicabortions in cattle and sheep. Their associ-ation with human blood cultures in the late1950’s was rare and hence Campylobacter spp.was deemed to be an opportunistic humanpathogen. It is only in the last 30 years thatthese organisms have been recognised as amajor cause of human illness. Campylo-bacters may have been observed in thestools of diarrhoeic infants in Germany asearly as 1880. The first recognised identifi-cation was made by McFadyen and Stockman

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in 1913 (cited in [102]) in association withabortions in sheep. Confirmatory tests werecarried out by Smith in 1918 (cited in [102])when similar organisms were isolated fromaborted bovine foetuses. The organismswere originally assigned to the Vibrio genus,due to their spiral appearance and henceSmith named the organism Vibrio fetus.However, it was not until 1947 that thehuman infection was first associated withthe microaerophilic vibrios, which wasassociated with a pregnancy-related infec-tion, where the fœtus died. In 1957, thework of Elizabeth King (cited in [102]) pro-posed two different types of vibrios associ-ated with enteric diseases, the first being V.fetus and the second was found to be ther-mophilic in nature. It was not until 1963 thatthe genus Campylobacter (meaning “a curvedrod”) was proposed as it realized that theorganism could not utilize sugars and had adifferent G+C content to that of Vibrio spp.The work of King was later corroboratedwith the work of Dekeyser and Butzler in1972 (cited in [102]), when isolation pro-cedures for thermophilic campylobacterswere developed. This method involved thefiltering of stools samples through 0.64 µmembrane filters and inoculating the filtersonto agar. This method proved too cumber-some and in 1977, Martin Skirrow fromWorcester Public Health Laboratory,described a simple direct technique, involv-ing the direct culturing of faeces onto bloodagar containing vancomycin, polymyxinand trimethoprim [153–156]. Plates wereincubated at 43 °C in an microaerophilicatmosphere containing 5% (v/v) O2, 10%(v/v) CO2 and 85% (v/v) N2. Since then,several methodological modifications havebeen made, thereby allowing the universaladoption of such methods and variants ofstandard methods, which allow routinediagnostic clinical microbiology laborato-ries to attempt the isolation of campylo-bacters from faecal specimens.

The improved isolation methods led tothe publication of the first report of the fre-quency of campylobacters in associationwith humans, thereby leading to an avalanche

of epidemiological research and conse-quently to the realization that campylo-bacters have now emerged as a significantpublic health problem for both developedand underdeveloped countries [44, 147,153–156, 165].

3. CLINICAL ASPECTS OF CAMPYLOBACTER INFECTIONS

3.1. Enteric infection

Thermotolerant campylobacters (Campy-lobacter jejuni/Campylobacter coli) consti-tute the most frequent cause of intestinalinfections worldwide. The main symptomobserved is diarrhea which can vary fromlimited to voluminous stools which may bewatery or bloody. Another frequent digestivetract symptom is abdominal pain, whereasvomiting is uncommon. Fever, headache,asthenia, and anorexia are also present andmay precede diarrhea [97]. Campylobactersare enteroinvasive bacteria which lead tocolitis and, in some instances, resembleinflammatory bowel disease. When pain isthe major feature of the infection, differen-tiation from appendicitis may be difficult.Normally the disease develops two to threedays after ingestion of contaminated foodand the symptoms resolve themselveswithin a week. In comparison to Salmonellaor Shigella infections, Campylobacter infec-tions are usually less acute (less fever andgeneral symptoms) with a higher tendencytoward recurrence if no treatment is given;however, they are not distinguishable with-out performing a coproculture. Stools remainpositive for several weeks. Treatmentappears to be beneficial if it is administeredearly enough in the course of the disease[146]. The recommended drugs are eryth-romycin, or amoxicillin or a fluoroquinoloneor tetracycline, provided the bacterium hasnot acquired a resistance.

Campylobacter enteritis may occur in allage groups but clinical presentation canvary according to age. In infants, the risk of


dehydration or convulsion exists. Breastfeeding protects against the clinical expres-sion of the infection [105]. Symptoms appearduring the weaning period.

In hyperexposed subjects, immunitydevelops and the infection becomes sub-clinical. It occurs in developing countries inchildren who are repeatedly infected butalso in certain populations in Western coun-tries, e.g. raw milk drinkers and workers inpoultry abattoirs.

In contrast, a decreased immune response,as may occur in elderly people or in peoplewhose immunity is impaired by an underlyingdisease (diabetes, cirrhosis, cancer, immu-nosuppression, HIV infection), increasesthe risk of developing a severe infection. Ina study, the risk of Campylobacter infectionwas multiplied by 40 when subjects wereHIV positive compared to controls [160].

For unknown reasons, the male gender isalso an important risk factor for Campylo-bacter infection. Furthermore, a decreasedgastric acidity, for example following pro-ton pump inhibitor consumption, has beenshown to be a risk factor [106]. A few localcomplications have been documented suchas appendicitis, peritonitis, cholecystitis,hepatitis or pancreatitis but are extremelyrare.

The main Campylobacter species involvedis C. jejuni which is responsible for 80 to85% of all enteric Campylobacter infec-tions. C. coli ranks second (10 to 15%).Although the latter’s source may be differ-ent, pigs being the main reservoir, this doesnot seem to lead to a different type of dis-ease. The other campylobacters such asCampylobacter lari, Campylobacter upsa-liensis, and Campylobacter fetus are moreseldomly found, but vary depending on dif-ferent regions of the world. C. upsaliensis,for example, is frequently isolated in SouthAfrica [69].

3.2. Systemic infection

Campylobacters are invasive bacteriawhich may translocate and reach the blood

flow. Nevertheless, the frequency of septi-cemia detected in the case of Campylo-bacter enteric infections remains very low(0.1%), especially when compared to thoseassociated with Salmonella [156].

There is one Campylobacter species, C.fetus, which is rarely found as a cause ofenteritis but is quite often isolated in sys-temic infections. The number of systemicinfections observed with C. fetus indeedexceeds the number due to thermotolerantcampylobacters. However, more than halfof the patients harbour an underlying dis-ease, as indicated previously. This bacter-iemia induces fever and leads to metastaticlocalization. A number of tissues can beinvolved, especially the vascular endothelium(aneurism, thrombophlebitis, endocarditis),bones, joints, meninges, etc. Despite itsname, C. fetus does not appear to induce fre-quent abortions in humans, only a few caseshave been reported. These infections mustbe treated vigorously because of a bad prog-nosis. In a survey of more than 100 cases,death occurred in 15% of the cases, one-third being attributable to the infection, anda relapse occurred in 10%. The proposedtreatment includes gentamicin and a secondantibiotic, e.g. amoxicillin or Augmentin®

or ciprofloxacin or imipenem, according tothe location and the susceptibility profile.

3.3. Post-infectious manifestations

As with other enteropathogenic bacteria,C. jejuni can cause post-infectious manifes-tations, e.g. reactive arthritis, urticaria, ery-thema nodosum. Interestingly, a case ofimmunoproliferative small intestinal dis-ease associated with C. jejuni has also beendescribed recently [74]. These complica-tions seldomly occur (< 1%). The mostimportant post-infectious manifestation tobe considered is Guillain-Barré syndrome[157]. This syndrome is an acute demyeli-nating disease affecting the peripheral neuronsand is characterized by an ascending paraly-sis. Three clinical forms can be distinguished,the last one being the Miller Fisher syn-drome, where ataxia and ophthalmoplegia

Campylobacter 355

are observed. C. jejuni enteritis is the infec-tion most frequently observed before Guil-lain Barré syndrome and occurs in 30 to50% of all cases. It is estimated to occur in1 in 3 000 C. jejuni infections. The patho-genic mechanism relies on antigen mimicrybetween oligosaccharides from the C. jejunilipopolysaccharides and the GM1 ganglio-side of the peripheral neuron membrane[195]. The serogroup first described inJapan is C. jejuni PEN19 but other sero-groups have been described in Europe [37].This syndrome is very severe, leading to a2 to 3% mortality and major neurologicalsequelae in 20% of the cases. The otherpatients experience a partial or total recov-ery [22]. The most severe cases are inducedby C. jejuni [77, 183].

Recently, Helms et al. [59] in Denmarkevaluated the global mortality rate of patientsin the year following a bacterial entericinfection, after an adjustment on comorbid-ity, and surprisingly found an excess mor-tality after Campylobacter infection (OR =1.35, 95% CI = 1.02–1.80).

In summary, Campylobacter infectionsare very common self-limited diseases.Their frequency generates numerous healthcare expenses. Furthermore, life-threaten-ing systemic diseases are diagnosed moreand more readily and the most severe Guil-lain Barré syndromes are the post infectiousconsequence of this infection, makingCampylobacter infection a major publichealth issue.

4. HUMAN EPIDEMIOLOGY AND FOODS OF ANIMAL ORIGIN

Campylobacter jejuni is now recognisedas one of the main causes of bacterial food-borne disease in many developed countrieswith Campylobacter coli less frequentlyimplicated [43]. Foods of animal origin, inparticular poultry, have been identified assignificant sources of this enteropathogenas a result of infection and contamination atthe pre-harvest and harvest levels [126].

The handling and consumption of poultrymeat has been previously linked to humanillness [8, 9], especially when eaten raw andundercooked or recontaminated followingcooking.

4.1. Campylobacters and poultry

The role of poultry in the epidemiologyof human Campylobacteriosis was clearlydemonstrated in Belgium during the dioxincrisis in 1999. As a result detecting feedscontaminated with abnormally high levelsof dioxins in feeds, domestically producedchicken and eggs were withdrawn fromretail outlets in Belgium. The resulting tem-porary deficit in supply of poultry and eggsover subsequent months resulted in an esti-mated 40% reduction in the numbers ofhuman Campylobacter cases reported. Theincidence of Campylobacter cases rose tosimilar levels to those observed prior to thecrisis when the ban on poultry meat waslifted [182].

Intestinal colonisation in broiler chicksis rarely detected until at least 7 days of age.Once colonised, chicks normally remainasymptomatic carriers until they reachslaughter age [51]. Wide variations in flockinfection prevalences up to 100% have beenpreviously reported in surveillance studies[64]. The most significant routes of trans-mission by Campylobacter to commercialpoultry flocks at the pre-harvest levelremain unclear. However, a number of epi-demiological studies have suggested thatinadequate disinfection between chick place-ments, age disposition, the use of multi-unitsites, the proximity of other livestock, sea-son and lapses in biosecurity are significantrisk factors [21]. The role of other vectorssuch as litter beetles, house flies and wildbirds have also been identified as potentialtransmission risks [27]. Conflicting reportshave emerged on the ability of campylo-bacters to infect successive generations eitherby direct vertical transmission from hen tochick via the egg or by horizontal transmis-sion within the hatchery environment [125,162]. Difficulties in the identification of


significant infection routes to commercialflocks at farm level have been further com-pounded by the strain diversity observed inboth flock and environmental isolates fromvarious studies and the frequently observedco-infection of birds with multiple strainsof Campylobacter jejuni [108, 125]. Theuse of contaminated water for drinking inpoultry houses has also been recognised asa significant risk factor for colonisation byCampylobacter and may in fact be under-estimated due to the existence of viable-non-culturable or highly stressed forms ofthe organism in environmental samples,including farm water supplies [109].

The high prevalence of campylobactersin poultry flocks at the pre-harvest level isfurther exacerbated due to multiple oppor-tunities for cross-contamination to occurduring slaughter and processing. The highthroughputs of modern poultry slaughterplants has necessitated the development ofautomated equipment in, for example, thestages of scalding, plucking and eviscera-tion. The net effect of processing large num-bers of carcases from different sources veryoften leads to the dissemination of entericpathogens, including Campylobacter fromthe early stages of the slaughtering process.Also, as skin is normally not removed fromdressed carcases, large numbers of campy-lobacters can remain in situ on the finishedraw product thus increasing the likelihoodof exposure to the consumer.

4.2. Campylobacters and other food animals

The gastrointestinal tracts of other foodanimal species have also been shown to befrequently colonised with campylobacters,particularly, C. jejuni and C. coli [99].Reported rates of intestinal Campylobactercarriage in food animals have varied widelybetween studies [23]. The digestive tract ofclinically normal cattle has been demon-strated to be a significant reservoir for a numberof Campylobacter spp. [12], with prevalencesof the enteropathogen in cattle ranging from0–80%. Prevalences of Campylobacter in

sheep have been shown to be generallylower with approximately 20% of animalsintestinal carriers [197]. The high preva-lences of campylobacters in pigs have beenreported previously in numerous studiesand dressed pig carcases have been shownto be more frequently contaminated thaneither beef or sheep [107]. This is mostlikely attributable to the fact that pig car-cases undergo a communal scalding stageearly in the slaughter process combinedwith the fact that the skin remains on thecarcase following all of the dressing proce-dures.

Contaminated shellfish have also beenimplicated as a vehicle in the disseminationof Campylobacteriosis. Harvesting shellfishfrom Campylobacter-contaminated waterswould appear to be the most likely cause ofinfection [193]. Campylobacters have alsobeen isolated frequently from asympto-matic companion animals, with symptomsof enteritis frequently reported in youngeranimals [56]. Transmission of campylobactersfrom pets to humans has been confirmed inprevious case studies and identified as apotential risk factor in epidemiological inves-tigations, particularly young children incontact with puppies exhibiting enteriticsymptoms [158].

4.3. Control in foods of animal origin

A longitudinally integrated approach tocontrolling campylobacters along the entirefood chain should be adopted for foods ofanimal origin, in particular, poultry. Con-trol should be directed primarily at the pre-vention of colonisation in food animalsthrough the implemention of Good Hygi-enic Practices (GHP), biosecurity measuresand husbandry practices which should beincorporated in Hazard Analysis CriticalControl Point (HACCP) based risk man-agement systems [189]. Efforts at harvestlevel should be concentrated on practicesdesigned to control and reduce levels of faecalcontamination during live bird transporta-tion, slaughter and carcase dressing [9, 191].In addition consumers and food handlers

Campylobacter 357

should be made aware of the role that theyplay in reducing the incidence of Campylo-bacter infection by preventing cross-con-tamination in kitchens or food preparationareas [61].

Other potential options currently availa-ble to reduce the levels of this enteropath-ogen on food animal carcases include, irra-diation [100], chemical decontamination[190], steam pasteurization and hot waterimmersion [192].

More recently, l’Agence française desécurité sanitaire des aliments (AFSSA)has published an extensive review articleentitled “Appréciation des risques alimen-taires liés aux Campylobacters: Applicationau couple poulet/Campylobacter jejuni”,which should be consulted for further infor-mation. This may be obtained on-line athttp://www.afssa.fr.

5. ENVIRONMENTAL CAMPYLOBACTERS

5.1. Water

Waterborne outbreaks associated withcontamination of drinking water by Campy-lobacter jejuni are rather common in theNordic countries Sweden, Norway or Fin-land, where in sparsely populated districtsgroundwater is commonly used withoutdisinfection. Campylobacters, Escherichiacoli, or other coliforms have rarely beendetected in potential sources. Using a com-bination of Penner serotyping and pulsed-field gel electrophoresis (digestion withSmaI and KpnI), Hanninen et al. [57] stud-ied three waterborne outbreaks in Finlandcaused by C. jejuni and used sample vol-umes of 4 000 to 20 000 mL for analysis ofCampylobacters and sample volumes of 1to 5 000 mL for analysis of coliforms andE. coli, depending on the sampling site,confirming the likely reservoir of an out-break. Poor water quality, sanitation andhygiene account for some 1.7 million deathsa year world-wide (3.1% of all deaths and

3.7% of all DALY’s), mainly throughinfectious diarrhoea. Gastrointestinal dis-eases are often severe due to under-nutritionand lack of intervention strategies in thedeveloping nations and virtually 9/10 accountfor infant deaths alone [11]. Major entericpathogens in the infant’s mortality includerotavirus, Campylobacter jejuni, enterotoxi-genic bacteria (Escherichia coli, Shigellaspp. and Vibrio cholerae 01) and possiblyenteropathogens (E. coli, Aeromonas spp.V. cholerae O139) enterotoxigenic Bacte-roides fragilis, Clostridium difficile andCryptosporidium parvum. All except theC. parvum are easily controlled by chlorin-ation of water, but re-contamination oftreated water is a huge problem. Emergingenvironmental pathogens, such as Helico-bacter pylori and Burkholderia pseudomallei,may well be of significance in someregions. In adults, much less is understoodof various sequelae such as myocarditis,diabetes, reactive arthritis and cancers somemonths-years after initial infections. Also,besides the traditional pathogens (helminths,Entamoeba histolytica, Giardia lambliahepatitis A and E) various enteroviruses,C. jejuni and H. pylori are emerging issuesin adults.

5.2. Sewage and water treatment plants

The presence of bacterial pathogens(Listeria monocytogenes, Campylobactercoli and jejuni, Escherichia coli O157 andSalmonella spp.) in eight Swedish sewagetreatment plants (STP), with four differenttreatment methods, focusing on detectionof zoonotic bacteria in raw and treatedsludge were investigated [142]. Restrictionenzyme analysis and pulsed field gel elec-trophoresis of Salmonella serotypes indi-cated that Salmonella persists in STP andthat there is a continuous supply of newstrains. There are differences in treatmentmethods concerning the reduction of path-ogens and indicator bacteria. If spread onarable land, sludge increases the environ-mental load of pathogens and therebyincrease the risk for spreading diseases to


people and animals. Said et al. [143]reported outbreaks of infectious diseasesover the last 30 years associated with pri-vate water supplies (PWS). The majority(16 outbreaks) were reported after the intro-duction of enhanced surveillance. AlthoughPWS only serve 0.5% of the population,36% of drinking water outbreaks are asso-ciated with PWS. The main pathogen,Campylobacter, was implicated in 13 (52%)outbreaks. Most reported outbreaks (88%)occurred in commercial or Category Twosupplies, which potentially affect largerpopulations. The main factors implicated inthese outbreaks are temporary or transientpopulations, treatment (lack or failure), thepresence of animals and heavy rains. Thepublic health problem associated with PWScould be prevented by the identification andunderstanding of risk factors, by the properprotection of water sources and adequatetreatment and maintenance. This could befacilitated through the introduction of a riskassessment as part of a scheme for the watersupplies. Ottoson [120] investigated theprevalence of pathogens (e.g. rotavirus,Salmonella typhimurium, Campylobacterjejuni, Giardia lamblia and Cryptosporidiumparvum) in greywater in a local treatmentsystem at Vibyasen (north of Stockholm,Sweden) and the faecal load of these path-ogens and were used to form the basis of ascreening-level quantitative microbial riskassessment (QMRA) using faecal indicatorbacteria and chemical biomarkers. Growthconditions for Salmonella in greywater sed-iments were also investigated and risk mod-elling based on replication in the systemincreased the probability of infection fromSalmonella 1000-fold, but it was still lowerthan the risk of a rotavirus infection. Themicrobial quality of several, usually untreated,surface domestic water sources, used byrural communities in the Venda Region ofSouth Africa, was assessed to gauge theirfitness for human consumption and to high-light the possible impact of waterborne dis-eases. Salmonella, Shigella, Vibrio cholerae,Campylobacter, Aeromonas and Plesio-monas were isolated from several of the

water sources investigated. The use of thesewater sources for drinking and domesticpurposes poses a serious threat to the healthand well-being of the users and calls forurgent South African government interven-tion [112].

5.3. Farms

Campylobacter is the most commonlyreported notifiable disease in New Zealand.Savill et al. [150] investigated the reservoirsof Campylobacter in a defined geographi-cal area within New Zealand and comparedstrains isolated from humans and environ-mental sources within this area as a preludeto investigating the likely transmissionroutes to humans. Campylobacter jejuni wascommonly found in faeces from dairy cows,beef cattle, sheep and ducks, chicken car-casses, sheep offal and surface waters andC. coli was commonly found in sheep fae-ces. Minihan et al. [99] reported that theprevalence of Campylobacter spp. faecalshedding within pens was positively corre-lated to the pen, the month of sampling andthe Campylobacter spp. contamination sta-tus of the pen dividing bars and the watertrough surface. They suggested that Campy-lobacter spp. should be considered as apathogen shed in the faeces of a substantialproportion of feedlot cattle. Guan and Holley[55] reviewed available international dataand the developing situation in WesternCanada upon the survival of major patho-gens including Escherichia coli O157:H7,Salmonella, and found significant variabil-ity in resistance to environmental challengethat are characteristic of the organisms them-selves. The survival of pathogens werelonger in environmental samples at cooltemperatures but their abilities differedwhen exposed in liquid and solid manure.Theoretical extrapolations from cattle manureenvironments, indicated that holding manureat 25 °C for 90 days would appear to renderthe cattle manure pathogen-free. However,with good hygienic practice during harvest,a very low level of this pathogen can beachieved on dressed carcasses. Poultry,

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particularly chickens, account for the major-ity of human infections caused by Campy-lobacter. Reduction or elimination of thispathogen in the poultry reservoir is an essen-tial step in minimizing the public healthproblem. However, farm-based interven-tion measures are still not available becauseof the lack of understanding of the ecolog-ical aspects of C. jejuni on poultry farmsand Sahin et al. [141] have elaborately dis-cussed the horizontal and vertical transmis-sions of Campylobacter infections affectedby immune status of the poultry host and theenvironmental conditions in the productionsystem. Eifert et al. [36] compared varioussampling techniques (cloacal swabs, faecalsamples and environmental surface “drag”swabs) on 3, 5 and 7 weeks old poultry birdsfor presence of Arcobacter butzleri, acausal agent of human enteritis and foundthat environmental swabs recorded thehighest percentage recovery, while intesti-nal tracts had none. Gaynor et al. [47] dem-onstrated via gene expression studies thecapacity of C. jejuni to adapt to multipleenvironmental niches. The genetic evolu-tionary mechanisms of adaption providesthe first whole-genome molecular explora-tion of the effect of laboratory culture andstorage on colonization and virulence prop-erties of this pathogen. In this respect, it isinteresting to note that Campylobactercases occurring in rural populations ofMichigan, USA, attributable to poultry hus-bandry and of some cases occurred in indi-viduals who were not poultry farmers byoccupation, is highlighted by the studies ofPotter et al. [131].

5.4. Food related environments

Novel employment of lactate dehydroge-nase release from porcine aortic endothelialcells (PAEC) as a quantitative marker ofcytotoxic activity in thermophilic Campylo-bacter spp. including Campylobacter jejuni,C. coli, C. lari and urease-positive ther-mophilic campylobacters (UPTC), fromhuman faecal isolates, poultry and environ-mental sources has been demonstrated by

Millar et al. [98]. Enterobacteriaceae andCampylobacter jejuni, were determined byquantitative real-time PCR (qPCR) than bycultivation [73], as some of these bacteriamay have been in a potentially hazardousactive but non-cultivable state and thismethod provides a viable alternative forbiosafety and hygiene monitoring reasons.Yang et al. [194] reported that retail chickenmeat, raw milk and environmental water arecommonly contaminated with C. jejuni andcould serve as a potential risk for consumersin eastern China, especially if proper hygi-enic and cooking conditions are not main-tained. The rapid and sensitive detection ofC. jejuni is necessary for the maintenanceof a safe food/water supply in China and thereal-time PCR assay provides a specific,sensitive and rapid method for quantitativedetection of C. jejuni. Pearce et al. [124]reported that although Campylobacter ishighly prevalent in the intestinal tracts ofswine arriving at the slaughter facility, thismicroorganism does not progress throughthe slaughtering operation and is not detect-able on carcasses after overnight chilling.Sharma et al. [152] critically examined thepotential of emerging water-borne patho-gens in both developed and developingnations and the global epidemiology of anumber of cases involving hepatitis viruses(including hepatitis E virus), Campylo-bacter jejuni, microsporidia, cyclospora,Yersinia enterocolitica, calciviruses andenvironmental bacteria like Mycobacteriumspp., Aeromonads, Legionella pneumophilaand multidrug-resistant Pseudomonas aer-uginosa that have been associated withwater-borne illnesses. It also examines thepossible reasons, such as an increase in thenumber of immunocompromised individu-als, urbanization and horizontal gene trans-fer, that may underlie their emergence. Theisothermal amplification method nucleicacid sequence-based amplification (NASBA),which amplifies RNA, has been reported asuseful for the detection of microbial patho-gens in food and environmental samples [29].

More recently Birk et al. [18] have devel-oped a food-based model system which is


a suitable model system for the study of sur-vival of C. jejuni in food systems. Thismodel employs chicken juice as the testmatrix and may be useful in anticipating thesurvival of C. jejuni in foods, thereby lead-ing to the development of new preservationsystems.

6. ATYPICAL CAMPYLOBACTERS

In relation to human Campylobacteriosis,C. jejuni, C. coli, C. upsaliensis, C. hyoin-testinalis, C. lari, C. fetus, C. sputorum bio-var sputorum have been demonstrated to beimplicated as gastrointestinal pathogens,though some are rare [71]. C. concisus, C.curvus, C. gracilis, C. rectus and C. showaeare detected in association with the oral cav-ity [82]. Alternatively, C. mucosalis, C. hel-veticus and C. sputorum biovar faecalis areisolated from animals [114, 161].

Moreover, some other atypical andemerging Campylobacter organisms thanthose described above have interestinglybeen identified to occur for these ten years.Therefore, the aim of the present article isto review atypical and emerging examplesamong the genus. Five years after, follow-ing the original description of C. lari organ-isms by Skirrow and Benjamin in 1980[155], Bolton et al. [20] isolated the first 10atypical isolates of C. lari, urease-positivethermophilic Campylobacter (UPTC) fromthe natural environment in England in 1985[20]. This was the first example of urease-producing bacteria among the genusCampylobacter. Then, four UPTC isolateswere found for the first time from humans,two from the faeces with two diarrheal dis-eases, one from the appendix with oneappendicitis and one from the urine withone urinary tract infection in 1986–1989[17, 96]. Until now, only these four clinicalcases of UPTC isolates have been pub-lished. However, any association of UPTCwith human disease still remains unclear.UPTC organisms were demonstrated tobelong within C. lari possibly as a biovar[122] or a variant [96]. After these descrip-

tions of UPTC appeared, isolates of UPTChave been reported in several Europeancountries (The Netherlands in 1997 [39],Northern Ireland in 1996, 1999 and 2003[66, 93, 193], England in 1998 [42]) and oneAsian country (Japan in 1996 and 2002 [92,94]). Consequently, about 200 UPTC isolateshave been found from the natural environ-ment, river water, sea water and shellfish,including wild birds, but not from anydomestic or wild animals. Therefore, thenatural environment is an important reser-voir of the UPTC organisms. However, ina study by Waldenstrom et al. [184] wereunable to detect any UPTC organisms in awild bird population in Sweden.

When On and Harrington studied thetaxonomic and epidemiological relationshipamong Campylobacter species by numeri-cal analysis of amplified fragment lengthpolymorphism (AFLP), a high level ofgenetic diversity in C. lari, particularlyamongst UPTC isolates, was identified [117].Multilocus enzyme electrophoresis analy-sis, which were shown to be the most suc-cessful at discriminating UPTC organismsat the subspecies level, whereas serotyping,phage-typing, antibiogram typing and flag-ellin typing were unsuccessful [101], alsodemonstrated that the UPTC isolates (n = 31)isolated from several countries and sourcesexamined are genetically hypervariable andform a cluster separate from the C. lari(n = 3) cluster [94].

In relation to the pathogenesis, Sekizukaet al. [151] has found short flaA-likesequences, containing internal terminationcodons (TAG), incomplete genes or pseu-dogenes of flaA in two Japanese UPTC iso-lates [151]. Furthermore, shorter flaA geneswithout any internal termination codons thanthose of C. jejuni and C. coli were demon-strated in the isolates of UPTC from the nat-ural environment in England [151] and inNorthern Ireland (T. Gondo, unpublisheddata). The reason(s) why any of UPTCorganisms have not been identified as acause of gastrointestinal disease for humans,may partly be due to the shorter and/or

Campylobacter 361

shorter pseudogene structure of flaA. Nophenotypic and genotypic characteristics ofurease from UPTC have yet been described.

In 1983–1985, C. hyointestinalis organ-isms, distinguished from previously describedcatalase-positive Campylobacter speciesby colony morphology, ability to produceH2S in triple sugar iron agar, glycine toler-ant, intolerant to 3.0% NaCl, ability to grow25 °C, sensitive to cephalothin and resistantto nalidixic acid, were first isolated from theintestines of pigs with proliferative enteritisand other animals (faeces from cattle andintestine of a hamster) [49, 50]. About tenyears after from the first description of C.intestinalis, seven isolates resembled butdistinct from the type strain and other refer-ence strains of C. intestinalis were obtainedfrom porcine stomachs [116]. Based on thenumerical analysis of 38 phenotypic char-acters, DNA-DNA hybridization studiesand DNA base compositions, On et al. [116]proposed the name C. hyointestinalis subsp.lawsonii. Alternatively, C. hyointestinalissubsp. hyointestinalis was accordingly given[116]. When Harrington and On examinedphylogenetic relationships of C. hyointesti-nalis subspecies by means of 16S rDNAsequences, they found that the sequenceidentities among C. hyointestinalis subsp.lawsonii isolates exceeded 99.9% and amongC. intestinalis subsp. hyointestinalis iso-lates ranged from 96.4 to 100% [58].Sequence identities between isolates repre-senting the two subspecies ranged from95.7 to 99.0%. Surprisingly, an interventingsequence was identified in the C. hyointes-tinalis subsp. lawsonii strains [58]. AFLP fin-gerprinting method was also demonstratedto allow the classification of the C. hyoin-testinalis at the subspecies level [35].

When, in 1998, Lawson et al. [70] exam-ined saliva and faeces from 20 healthy indi-viduals in order to know the variety ofcampylobacters in their gastrointestinaltract, PCR assays specific for nine speciesof Campylobacter (C. sputorum, C. concisus,C. upsaliensis, C. helveticus, C. lari, C. fetus,C. hyointestinalis, C. jejuni and C. coli),

and for the genus as a whole was performed[70]. Three unidentified 16S rDNA Campy-lobacter genus-specific amplicons of faecalorigin were sequenced and demonstrated tobe 99% similar [70]. These were previouslyundescribed and uncultivated Campylo-bacter species. The organism from faeces,specific PCR assay, was detected in 10 ofthe 20 faecal samples but not in any salivasamples. Then, the authors proposed toterm “Candidatus Campylobacter hominis”[70]. Nextly, they developed an isolationstrategy employing initial non-selectivemembrane filtration onto fastidious anaer-obe agar for the uncultivated C. hominisorganisms [72]. The unique species statusof the isolates, whose nearest phylogeneticneighbours were C. gracilis and C. sputo-rum, was further confirmed by taxonomicstudy of 47 phenotypic characteristics [72].

C. lanienae is a new catalase-positivespecies that was first described from thefaeces of healthy abattoir workers in Swit-zerland in 2000 [81]. Nucleotide sequenceof the 16S rDNA, DNA-DNA homologytest and G+C content of genome DNA dem-onstrated that the new organism constituteda previously undescribed species, whose near-est phylogenetic neighbours were C. hyoin-testinalis subsp. hyointestinalis, C. fetusand C. mucosalis [81]. Rapid PCR-biprobeidentification scheme based on the real-time PCR was developed for the Campylo-bacter taxa pathogenic for humans, includingC. lanienae [82]. This new organism hasalso been isolated from the faeces of sixhealthy pigs in Japan [148] and from thefaeces of bovine and beef cattle, in the beefcattle, C. lanienae was the most frequentlydetected species (49%), in Canada [62, 63,115, 118]. In addition, an interveningsequence of 226 bp in the 16S rDNA wasfound in four isolates of the six of C. lan-ienae in Japan [148].

In 1998, On et al. first identified the15 strains isolated from faeces of 14 cattlein United Kingdom and one human diar-rhoea in Canada among 44 catalase nega-tive and urease-positive Campylobacter


group as a new C. sputorum biovar parau-reolyticus, by a phylogenetic study basedon phenotypic characterization, numericalanalysis of whole-cell protein profiles, DNA-DNA hybridization and sequence analysisof 16S rDNA [115]. They demonstrated theclonality of C. sputorum bv. paraureolyticsdetermined by macrorestricion profilingand biotyping by using the 18 isolates iso-lated over a 12-month period from sevendairy cows contained in a single herd [181],Their study also indicated that the organismcan persist in cattle for a long-term, at least12 months.

Alderton et al. in 1995 [5] reported the11 isolates from intestinal lesions of pigswith proliferative enteritis including anorganism formerly described as strain RMIT32AT as a new name C. hyoilei sp. nov. [33].The phenotypic characteristics of theseorganisms indicated that they are closelyrelated to each other and are not isolates ofother Campylobacter spp. commonly iso-lated from pigs. They also suggested thatthis organism is more closely related to C.jejuni than C. coli based on the sequencedifferences of 16S rDNA. However, it wasconfirmed that C. coli strains and C. hyoileistrains were indistinguishable based onexamining a variety of phenotypic and gen-otypic criteria and both represent the samespecies [180]. Although differentiationbetween C. hyoilei and C. coli using geno-typic and phenotypic analyses were dem-onstrated, the taxonomic subcommittee ofthe International Committee on SystematicProkaryotes finally concluded that the epi-thet ‘hyoilei’could in principle be revised asan infrasubspecific designation. Therefore,the subcommittee discouraged the use ofthe name C. hyoilei.

In conclusion, for the last ten years,about 200 UPTC isolates have found onlyin the natural environment in Europe andJapan, whereas several atypical and emerg-ing Campylobacter taxons (C. hominis,C. lanienae and C. sputorum subsp. parau-reolyticus) have been newly found mainlyin the faeces of healthy humans and domes-

tic animals (pigs, bovines and cattle) inEurope and North America (Canada), More-over, seven isolates of C. hyointestinalissubsp. lawsonii have been isolated from theporcine stomach in UK. Thus, healthydomestic animals including wild animalscould potentially be important reservoirs ofthese new atypical and emerging organismsof Campylobacter in humans.

7. ANTIBIOTIC RESISTANCE

Campylobacter enteritis is considered tobe a zoonotic disease, and domestic animalssuch as poultry, cattle and pigs can act assources of infection [59, 95]. Transmissionto man usually results in sporadic infection,and is often associated with improper han-dling or cooking of food. The majority ofcases of clinical Campylobacter enteritisare sufficiently mild or self-limiting not torequire antimicrobial chemotherapy [6].Nevertheless, in severe or recurrent caseswhere antibiotics are required, susceptibil-ity testing is important to ensure appropri-ate and timely treatment [13, 134, 179].Serious systemic infection may also betreated with an aminoglycoside such asgentamicin [153]. Tetracyclines have beensuggested as an alternative choice in thetreatment of clinical Campylobacter enteri-tis, but in practice are rarely used. However,macrolides remain the agents of choice, andresistance rates to erythromycin remaincomparatively low [104]. Fluoroquinolo-nes, offer an effective therapy, against mostenteric pathogens, to treat acute bacterialdiarrhoea; with ciprofloxacin being usedextensively as prophylaxis for travellers[52]. Emergence of resistance to theseagents however, has since made their effi-cacy less certain. Resistance was reportedto develop among patients after treatmentwith fluoroquinolones [14], and was alsofound to coincide with the introduction ofthese agents in veterinary medicine [1, 2,38]. However, an increasing number ofCampylobacter isolates resistant to thesedrugs are now being cultured from both

Campylobacter 363

clinical and food samples in several Euro-pean countries, Canada and the UnitedStates. Since the 1990s, a significant increasein the prevalence of resistance to macrolidesand fluoroquinolones among Campylo-bacter spp. have been reported and this isrecognised as an emerging public healthproblem in many European countries [40].Entry of these isolates into the food chaincould represent a significant threat to publichealth.

7.1. Antimicrobial susceptibility testing in Campylobacter spp.

Several laboratory methods, includingdisc diffusion, broth microdilution, agardilution and the Epsilometer-test (E-test)have been applied to determine in vitro sus-ceptibility profile(s) of Campylobacter to arange of antimicrobial agents [15, 41, 45,46, 48, 84, 119, 149]. Despite the availabil-ity of comparable standardised proceduresfor many organisms, based on, the approvedguidelines defined by the National Com-mittee for Clinical Laboratory Standards(NCCLS), no internationally accepted cri-teria for susceptibility testing of Campylo-bacter spp. are available and breakpoints donot exist. Consequently it is not possible todirectly compare the resistance profiles ofisolates cultured from various origins.More, recently however, the NCCLS Sub-Committee on Veterinary AntimicrobialSusceptibility Testing approved an agardilution protocol as a valid method.

Several authors have compared the per-formance of the methods above andreported a correlation between E-test andagar dilution methods. Values determinedhowever can vary depending on the antimi-crobial agent(s) being considered [48]. Thisobservation was particularly evident withrespect to C. jejuni [84]. Comparing MICvalues obtained by E-test and the agar dilu-tion protocols, Ge et al. [48] reported valuesranging from 21.4 to 62% for gentamicinand nalidixic acid respectively. Whilst theE-test is convenient, relatively simple toperform, MIC values determined by this

method are lower when compared to similarvalues obtained by the agar dilution methodregardless of the organism tested [41, 48, 60].However when E-test and the agar dilutionmethod are used on a small number of iso-lates from a single geographic location, accept-able agreement between both approachesfor susceptibility categorisation is achieved.For larger collections, microdilution is thepreferred protocol especially when suscep-tibility to nalidixic acid and trimethoprim-sulfamethoxazole are being considered [84].

Molecular techniques offer an alternativemeans of assessing antimicrobial resistanceamong bacterial isolates. In a study of qui-nolone-resistant Campylobacter a majorityof isolates analysed were shown to possessa common mutation [128]. The predominantgenetic alteration responsible for confer-ring resistance to ciprofloxacin in C. jejuniand C. coli is the result of a mutation in thegyrA gene, whereby many isolates testeddemonstrated a Thr-86-Ile substitution in theA-subunit of DNA gyrase [185]. A MismatchAmplification Mutation Assay (MAMA)-PCR has been successfully applied to thedetection of ciprofloxacin resistance inC. jejuni and C. coli, and this protocol is aconvenient screening tool among these iso-lates [196]. This method used a conservedforward primer and a reverse diagnosticprimer, which together generate a 264-bpproduct that is a positive indication of thepresence of the Thr-86-Ile amino acid substi-tution, consistent with resistance to cipro-floxacin. A “real-time” PCR-based approachwas recently developed to detect the C-to-Tnucleotide polymorphism associated withthe latter amino acid substitution in thegyrA-encoding gene [34]. In this case, fluores-cence resonance energy transfer technology(FRET) can be applied to the analysis ofmelting curves when a specific probehybridises to a DNA template. This proto-col can be adapted to include additionalmutations providing rapid and reproduciblescreening methods for ciprofloxacin resist-ant Campylobacter isolates.


Undoubtedly, one of the advantages ofusing these methods includes the possibil-ity of direct detection from a sample obvi-ating the need for culture [28]. Molecularmethods can facilitate analysis of organ-isms that may be sub-lethally damaged anddifficult to grow, and these strategies alsooffer the possibility of screening large numbersof isolates for a specific mutation within asingle assay. The disadvantages of usingmolecular detection methods include thefailure to detect resistance if a new, unexpectedor rare resistance mechanism is present[104], and the necessity to perform a sepa-rate assay for each antimicrobial agent tested.Furthermore, no standards exist for per-forming genetic testing methods [28]. Forthese reasons, it may be more useful to com-bine phenotypic and genotypic methods ofsusceptibility testing.

7.2. Surveillance of antimicrobial resistance in Campylobacter spp.

Transmission of antimicrobial resist-ance from food animals to humans canoccur via the food chain [126, 133]. It is dif-ficult to determine the precise extend of therisk posed to human health [127]. Neverthe-less, food animals are a significant reservoirof antibiotic resistant zoonotic pathogens.Continuous monitoring of susceptibility pro-files of Campylobacter spp. to a panel ofantimicrobial agents is necessary for a numberof reasons. Firstly, there are increasing ratesof resistance to the agents of choice used inthe treatment of clinical enteric infection[1]. This suggests a need to supply alterna-tive antimicrobials which remain therapeu-tically effective. Secondly, the emergenceof multidrug-resistant (MDR) organismsmust be monitored carefully [86]. Finally,mechanisms for the transfer of resistanceboth within Campylobacter spp. and betweendifferent genera of enteric organisms bymeans of mobile genetic elements maypresent a significant threat to the continuedefficacy of antimicrobial chemotherapy[76, 113].

The use of antimicrobial agents on farmanimals, both to treat infection and asgrowth promoters is a cause of concern, andthe increasing rates of resistance amongCampylobacter spp. to these agents appearto make a conservative policy on the use ofantibiotics in farm animals advisable [1,127]. Antibiotics of the macrolide-lincosa-mide group have been used in treating foodanimals worldwide for several decades.Their uses have included the control of dys-entery and Mycoplasma infections inswine, and for treating mastitis in cattle[40]. The use of macrolides and other com-pounds for growth promotion has beenbanned, in all European Union countrieswith effect from July 1999. Fluoroquinolo-nes are available for treating food animalsin many countries, and Table I shows theveterinary licensing “time-line” of this groupof antibiotics in a number of Europeancountries. It is difficult to evaluate the actualusage of these agents in food animals, but itis noteworthy that fluoroquinolone treat-ment of Campylobacter-colonised broilerchickens has induced fluoroquinolone resist-ance under experimental conditions [65].

Supplementing animal feed with antibi-otics is estimated to constitute more thanhalf the total antimicrobial use worldwide[188]. It has been reported that in Denmarkthe consumption (per animal) of antibioticssuch as macrolides and tetracyclines inagriculture was 2–4 times higher than con-sumption (per patient) in human medicine[1]. Emergence of antimicrobial resistanceamong zoonotic pathogens has led to thedevelopment of a continuous surveillancesystem of antimicrobial resistance amongbacteria isolated from pigs, cattle and broil-ers in Denmark. The Danish IntegratedAntimicrobial Monitoring Programme (DAN-MAP) has set out to establish a baseline forcomparison with future prospective studiesto enable the determination of trends overtime [1]. Monitoring strategies such as thismay have a positive impact on the effectivetreatment of human enteric Campylobacterinfection. To date, with the exception ofciprofloxacin resistance, there is a scarcity

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of scientific evidence for the transmissionof antimicrobial resistance as a direct resultof the use of antimicrobial agents in veter-inary medicine [127].

7.3. Genetic mechanisms associated with antimicrobial resistance in Campylobacter spp.

Bacterial populations can respond to thethreat of an antimicrobial agent by evolvingsome type of resistance mechanism(s) [138,159]. The imposed selective pressureresults in the development of a correspond-ing resistance determinant, either throughdirect acquistition or intrinsically by mod-ification of a host gene target, designed tofacilitate evasion of the inhibitory substance.For example environmental selection follow-ing enrofloxacin treatment of chickens infectedwith fluoroquinolone-sensitive Campylo-bacter spp. resulted in the emergence of thecorresponding resistant isogenic strainssuggesting that this organism is hypermutat-able under these conditions [87]. Horizontal

transfer of such resistance determinants(acquisition) together with any genetic mod-ification of pre-existing genes through pointmutations (intrinsic) or some other geneticevent, are thought to be the main mecha-nisms contributing to bacterial resistance[2, 10, 140]. Self-transmissible elementsincluding plasmids, transposons and bacte-riophage all facilitate the acquisition andsubsequent dissemination of resistancedeterminants. In addition, integrons, whenassociated with plasmids and/or bacteri-ophage are now considered efficient vehi-cles for the transfer of resistance markersamong unrelated bacterial populations [24].

The isolation rate of plasmids fromCampylobacter spp. has been shown to varyconsiderably between 44 and 91% for clin-ical and poultry isolates respectively in onestudy [75], compared with a plasmid isola-tion rate of 19% reported in a separate study[14]. As shown in Table II, tetracycline,kanamycin and chloramphenicol resist-ances are primarily plasmid-mediated. His-torically, tetracycline resistance has been

Table I. Veterinary licensing of fluoroquinolones in selected European countries.

Country Antimicrobial Licensing year Animal species

Ireland Enrofloxacin Prior to 1987 Cattle, pigs, poultry

United Kingdom EnrofloxacinDanofloxacinMarbofloxacin

Difloxacin

1993199319951998

Cattle, pigs, poultryPoultryCattle

Poultry

Denmark EnrofloxacinDanofloxacin

DifloxacinMarbofloxacin

1991199319981998

Cattle, pigs, poultryPoultry

Poultry, turkeyCattle, pigs, dogs, cats

Spain EnrofloxacinDifloxacin

19861998


The Netherlands EnrofloxacinDifloxacin

19871998


France EnrofloxacinDanofloxacinMarbofloxacin

Difloxacin

1991199619931998

Cattle, poultryCattleCattle

Poultry


particularly well researched and docu-mented [173] The tetO gene conferring tet-racycline resistance has a G+C content of40% [90], which is close to that of the tetMgene of Streptococcus pneumoniae, withwhich it shares 75% homology [89]. It issignificantly higher than that for C. jejuniand C. coli chromosomal (32.5 mol%) andplasmid (33 mol%) DNAs [90, 169]. Basedon this evidence, Taylor and Courvalin[168] have suggested that the tetO gene wasacquired by Campylobacter spp. from aGram-positive coccus, and that divergenceoccurred over time. More recently, in Brazil,

only 15.9% of the isolates analysed forplasmids contained these mobile elementsand none of the tetracycline resistant strainswere found to harbour plasmid DNA [10].

Chloramphenicol resistance, although rarein campylobacters [10], has also beenreported to be plasmid mediated [140]. A chlo-ramphenicol resistance determinant clonedfrom a C. coli plasmid was sequenced andfound to have 43 and 57% homology withchloramphenicol acetyltransferase (CAT) pro-teins from other Gram-positive and -negativeorigins [186]. A kanamycin resistance deter-minant, aphA-3 was found located distal to

Table II. Genetic mechanisms responsible for antimicrobial resistance detected to date in C. jejuniand C. coli.

Antibiotic Mechanism of resistance Reference

Aminoglycosides (with the exception of kanamycin)

Chromosomal: enzymatic modification of antibiotics.Integron-mediated resistance

[113, 175]

Kanamycin Majority plasmid-borne, remainder chromosomal; resistance through enzymatic modification of kanamycin

[140]

Chloramphenicol Plasmid-borne, resistance through modification of the target site (ribosome) or alteration of the antibiotic

[186]

Ciprofloxacin Chromosomal: modification of gyrA and parC confers resistance

[3, 4, 16]

Erythromycin Chromosomally mediated, resistance through modification of the target site (ribosome)

[166]

β-Lactams Chromosomal; three mechanisms, decreased uptake through modification of a porin, alteration of a penicillin binding protein, or production of a β-lactamase

[129]

Tetracycline tetO gene, plasmid-borne in the majority of cases, resistance mediated through ribosomal protection

[7, 78, 167]

Trimethoprim dfr1 gene, chromosomal, located to the remnants of an integron dfr9 gene, chromosomal, located to the remnants of a transposonResistance arising through modification of the trimethoprim target

[53]

Multidrug-resistance (MDR)

Efflux pump with a broad specificity; preventing accumulation of antibiotics

[25]

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this cat gene and Sagara et al. [140] reporteda link between kanamycin and chloram-phenicol resistance in Campylobacter fol-lowing a number of cloning experimentsinvolving the cat and kan resistance genesof a plasmid from a multiple-antibiotic-resistant C. coli isolate.

Kanamycin resistance in Campylobacteris more commonly associated with C. colithan with C. jejuni [140]. Like tetracyclineresistance, kanamycin resistance determinantswere located both on the chromosome andon self-transmissible plasmids [168]. Thesedeterminants are frequently found on thesame plasmids as tetracycline-resistancedeterminants [67, 170]. Kotarski et al. [67]also observed that the Kmr determinantcould translocate between plasmid andchromosomal DNA, suggesting that the Kmr

determinant in campylobacters may be locatedon a transposable element of approximately4 kb. A number of genes responsible forKmr in campylobacters have been identifiedincluding aphA-1, aphA-2, aphA-3 and aphA-7, with a plasmid location reported for bothaphA-3 and aphA-7 [168, 172]. The aphA-3 gene is often found on large plasmids thatalso encode tetO. aphA-3 like tetO isthought to have originated from a Gram-positive source and is commonly found instaphylococcal and streptococcal species[68]. aphA-7 determinants on the otherhand have been reported to be found onsmall plasmids that do not encode any otherresistance determinants [171]. AlthoughaphA-7 has been shown to have a broad hostrange, in that it can be expressed in bothE. coli and S. gordonii, its low G+C ratio(32.8%), matching that of C. jejuni, suggeststhis gene may be indigenous to campylobacters[172]. A chromosomal location for aphA-1has been reported for a Campylobacter-likeorganism [121]. Table II lists some of thepotential means by which Campylobacteracquires antimicrobial resistance markers.

Macrolides are the agents of choice fortreating Campylobacter infections. Resistanceto erythromycin is mainly found in strainsof animal origin, especially C. coli in pigs

and from chickens [40] and detection oferythromycin resistance may be determinedby PCR methods [163]. Nevertheless,erythromycin is considered to be one of thesafest drugs effective against Campylobacter.Resistance may also develop during thecourse of human treatment. Similar totetracycline (outlined above), erythromycinis a potent inhibitor of protein synthesis,binding reversibly to several ribosomaltargets including the Domain V-located onthe 23S rRNA gene locus, in addition to theribosomal structural proteins, L2, L4, L15and L22. Three major point mutationsoccuring within the former locus, andresponsible for erythromycin resistance,were defined [177]. The MIC in each casewere 128 µg/mL, as defined by the agardilution method. A combined PCR-RFLPassay was evaluated as a direct means ofdetection. Similarly, a PCR-based line-probeassay focusing on the 23S rRNA target only,was developed as a simple means to detectisolates resistant to erythromycin [111].Whilst useful, this approach detected only50% of mutations arising in resistant Japaneseisolates analysed. It is consieveable that notall of the mechanisms contributing tomacrolide resistance in Campylobacter havebeen described to date. The possibility arisesthat at least some of these will be MIC-dependent. Vacher et al. [177] did not considerthe possible involvement of the ribosomalstructural proteins, whereas Corcoran andFanning (unpublished) sequenced severalL4 and L22 genes and defined associatedpolymorphisms in resistant isolates. Noneof these isolates possesed any of thecorresponding nucleotide polymorphismsin the 23S rRNA gene. Similarly, theinvolvement of an efflux system (below)cannot be ruled out [88]. Inhibition of thispump system with phenylalanine-argineneb-naphthylamide (PAβN) was shown torestore susceptibility to Campylobacter ina dose dependent manner.

Fluoroquinolones are important drugsused in human and animal medicine, andare often the agents of choice used to treatcampylobacteriosis in humans. Currently,


in the European Union, fluoroquinolonesare licenced for use in a number of foodanimals, however emerging resistance to thisimportant class of antimicrobial is recognisedas a significant public health problem [128].This observation may in turn, lead to Campylo-bacter-associated deaths among vulnerablemembers in the community. Resistance tofluoroquinolones arises following a pointmutation [ACAATA], which produces aThr-86-Ile amino acid substitution in theQuinolone Resistance Determining Region(QRDR) of the gyrA subunit-encoding gene[185]. Genetic alterations in this region areoften associated with high-level resistanceto nalidixic acid (MIC > 64–128 µg/mL)and ciprofloxacin (MIC > 16–64 µg/mL).Similarly, resistance to fluoroquinolnes mayalso be associated with the activation of amulti-gene efflux pump system (see belowand [25]).

The presence of chromosomally-locatedtransposons among Campylobacter spp.had not been reported prior to 1998. Thedfr9 gene-encoding trimethoprim resist-ance was located to the remnant of a trans-poson inserted in the genome of a numberof clinical C. jejuni isolates, [53]. The G+Ccontent of dfr9 was found to be 40%, (sim-ilar to the tetO gene described earlier),which is considerably higher than that ofCampylobacter spp, and was previouslydetected in a transposon located in thegenome of porcine isolates of E. coli [26].A study by Richardson and Park [136] iden-tified an insertion sequence that wasflanked by direct repeat sequences in thechromosome of certain isolates of C. jejuni,which appeared to be a non-functionaltransposable element and the spread of anti-biotic resistance under natural conditionsimay be due to a combination of gene trans-fer systems acting in parallel or in series [30].

7.4. Gene cassettes and class 1 integrons in Campylobacter spp.

Integron structures are naturally occur-ring gene expression systems that canpotentially capture and integrate one or

more gene cassettes and convert them intofunctionally expressed genes [135]. It isthese gene cassettes that encode the resist-ance determinants to several antimicrobialagents [24].

Although several classes of integronshave been described to date, class 1 are clin-ically significant. A typical class 1 integronincludes two conserved segments (CS),known as the 5’- and 3’-CS segments,flanking the central gene cassette. An intIgene encoding an integrase enzyme islocated within the 5’-CS, which is respon-sible for the recombination of an incominggene cassette at a specific att1 attachmentsite. Also, within this region is a promoterwhich facilitates the efficient expression ofany integrated gene cassette. The 3’-CScontains two open reading frames (ORFs)encoding resistance to quaternary ammo-nium compounds (qac) and sulphonamide(sul1), respectively. Integrons can incorpo-rate and express more than one gene cas-sette, provided that its location is flanked bythe 5’- and 3’-CS domains. Thus integronsmay contain a number of recombined genecassettes, oriented in a classical “head-to-tail” arrangement, conferring a multi-drugresistant (MDR) phenotype on any isolatein which these genetic elements are located.

Previously, integron-like structures werereported in Campylobacter isolates raisingthe possibility that these elements mayencode antimicrobial resistance and possi-bly function as a potential vehicle for dis-semination of resistance among Campylo-bacter spp. [85]. Gibreel and Sköld [53],reported the existence of chromosomallylocated integrons carrying a dfr1 containinggene cassette (Tab. II) in C. jejuni. In arecent study investigating of a large collectionof unrelated Campylobacter spp., isolatesof both human and animal origin, completeclass 1 integrons were identified [113]. In thiscase, the gene cassettes contained twoORFs, one of which conferred resistance tothe aminoglycoside antibiotics, streptomy-cin/spectinomycin.

Campylobacter 369

As the use of aminoglycoside therapy maybe considered as an appropriate treatmentoption for some Campylobacter-relatedinfections, the recent identification of integronscontaining aminoglycoside-encoding genes(aadA2 and aac4), suggests that thepossibility now exists for treatment failureto occur, due to the presence of these geneticelements in Campylobacter spp. [76, 113].Furthermore, the presence of class 1 integronsin several Campylobacter isolates may inpart offer an explanation for the high levelsof resistance to sulphonamides, frequentlyreported among these organisms. Increasingprevalence of macrolide- and quinolone-resistance is more usually attributed to specificmutations in chromosomally located genes,though the future involvement of plasmidencoded integrons cannot be ruled out.O’Halloran et al. [113] suggest that integronsmay be partly responsible for horizontalgene transfer as a potential vehicle fordissemination of MDR phenotypes amongCampylobacter spp. These findings mayhave further implications for future therapeuticstrategies, leading to reduced drug efficacyand/or treatment failures in the case ofMDR organisms, whose transmission throughthe food chain poses a real threat to publichealth.

7.5. MDR-mediated by antimicrobial efflux systems

Active efflux pumps are known to con-tribute to intrinsic and acquired resistanceto a range of antimicrobial agents [79, 87,91]. These pumps reduce the intracellularaccumilation of antimicrobial agents andother compounds and this feature is nowrecognised as a major mechanism of resist-ance in pathogenic organisms [110, 130,178]. Comparitive genomics has identifieda number of efflux transporters and some ofthese are classified as H+-antiporters. InCampylobacter spp., the resistance to nod-ulation and cell division (RND) family[176] is associated with high-level fluoro-quinolone resistance [79, 132, 187]. Thisresistance is linked to the activation of the

Campylobacter-mediated efflux systemreferred to as the cmeABC-operon. Thisthree gene operon efflux pump system con-tributes to multidrug resistance (MDR) inC. jejuni and probably in C. coli also (Cor-coran and Fanning, unpublished) and con-sists of an inner-membrane transporter(encoded by the cmeC gene), a periplasmicfusion protein (cmeB) and an outer-mem-brane channel protein (cmeA). Susceptibil-ity studies by Lin et al. [79, 80] using wildtype and isogenic mutants in C. jejuni dem-onstrated that inactivation of the CmeABCpump by insertional mutagenesis substan-tially increased the susceptibility of C. jejunito several classes of antimicrobial agent(s)and also to heavy metals and bile salts [79].Resistance to bile salts may be a necessarystep for successful colonization of animalintestines, contributing to bacterial patho-gensis [87].

Efflux mechanisms have an importantimpact on antimicrobial resistance [187].Resistance by efflux can be easily dissem-inated [91]. In several cases the genetic ele-ments encoding efflux pumps and their reg-ulators are located on plasmids, or onconjugative or transformable transposonslocated on plasmids or in the chromosome.More importantly, efflux mediated resist-ance mechanisms can spread between phy-logenically very different species. This hasbeen exemplified by the macrolide-medi-ated efflux, not only among streptococci,but also to other Gram-negative bacteria[83]. Co-transfer with genes for other resist-ance classes may also take place if these arepresent together on large mobile geneticelements.

In conclusion, thermophilic Campylo-bacter spp. are among the commonest bac-terial cause of gastroenteritis in developedcountries. Our knowledge of this organismsepidemiology is limited. Campylobacterio-sis is a zoonosis, and farm and companion-animals are significant reservoirs of theorganism with the potential for transmis-sion to humans. There is evidence that freshmeat, especially poultry, is a major source


of infection [164]. In addition, antibioticresistant C. jejuni and C. coli are now beingreported with increased frequency [86,113]. Erythromycin and less commonly,ciprofloxacin, remain the agents of choicefor the treatment of severe or recurrentCampylobacter enteritis in humans. How-ever, it has been suggested by some inves-tigators that fluoroquinolone and macrolideuse in animals (for treatment and preven-tion) leads to the development of resistanceamong human isolates [38], whilst otherssuggested that resistance in C. jejuni andC. coli can be accounted for, at least in part,by use of antimicrobials to treat humaninfection. The association between the useof valuable drugs in veterinary medicineand the emergence of resistance in humanisolates and visa versa requires a more com-plete understanding.

Treatment with antimicrobials is a riskfactor for infection with organisms that aresimultaneously resistant to several drugsand this may contribute to mortality [59].Horizontal gene transfer is a significantmechanism for disseminating antimicrobialresistance among unrelated bacterialpopulations [10, 126]. Integron structuresplay a pivotal role and have been identifiedin several Gram-negative bacterial speciesincluding food-borne pathogens, such asSalmonella spp., E. coli and Shigella spp.[31, 138, 159]. Studies are now reportingthe existence of these structures in Campy-lobacter and therefore their role and contri-bution to antimicrobial resistance must beassessed [76, 113].

Overall, amplifying the reservoir ofresistance by whatever means is inherentlyproblematic, making transmission to humansvia food or other means more likely. Quan-titative evaluation of associated risks willlead to the development and effectiveimplementation of rational guidelines forantimicrobial use [59, 127]. EliminatingCampylobacter transmission via the foodchain must remain a veterinary and publichealth priority.

8. CAMPYLOBACTER DETECTION

Campylobacter species and in particularCampylobacter jejuni and Campylobactercoli are the most common cause of gastro-enteritis in humans in the developed world.Ever since its recognition as a cause of dis-ease in humans, detection of this zoonosishas relied on culture-based methods. Infact, the original development of a culturemedia for the isolation of Campylobacterfrom human faeces by Martin Skirrow in1977 [154] helped to firmly establish itsrole in human disease. Prior to this work,Campylobacter detection was reliant onmembrane filtration of faecal samples ontonon-selective media, a laborious and cum-bersome method. Although Skirrow’smedium was effective for isolating campy-lobacters from human faeces, it was lesssuitable for animal and environmentalspecimens, owing to the presence of con-taminating species. This led to the develop-ment of the more selective Preston mediumby Bolton and Robertson [19] suitable forthe isolation of Campylobacter from foodsand environmental samples. In subsequentyears following these publications, furtherimprovements have led to more sensitiveand selective media for the improved detec-tion of Campylobacter in faecal samples.

However, even with these improvementsculture-based methods have a number oflimitations. The methods are slow and in thecase of human faecal samples require up to48 h to yield a presumptive isolate, whichthen requires confirmation using pheno-typic tests. In the case of food samples,where cell numbers can be low in a back-ground of high numbers of other competingflora, enrichment culture in broth media isrequired to recover small numbers of cellsprior to plating on selective media. This canlengthen the detection process with up tofive days bring required to achieve a result.Culture-based methods may also select againstless common species, such as Campylobacterupsalienesis and Campylobacter lari, leadingto possible misdiagnosis and underestimation

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of the true burden of infection with theseother species.

The limitations of culture-based proce-dures led to the development of alternativemethods for the detection of campylo-bacters in foods and faecal samples. Thedevelopment of both poly and monoclonalantibodies specific for campylobacters hasfacilitated the development of a number ofantibody-based tests. Latex agglutinationtests for the identification of presumptiveCampylobacter isolates have been devel-oped, which can provide rapid more rapidspecies confirmation than conventionalphenotypic tests [103]. A commercial enzyme-linked immunosorbent assay (ProSpecTMicroplate assay; Alexon-Trend, USA)was developed for the detection of C. jejuniand C. coli directly in faecal samples, fromhumans with gastroenteritis [174]. Thisassay was demonstrated to have a sensitiv-ity of 96% and a specificity of 99% whenapplied to 50 Campylobacter culture-posi-tive and 114 culture-negative faecal speci-mens [174]. A second prospective study of1205 faecal samples demonstrated similarresults with a sensitivity of detection of97.7% [32]. The assay also provided morerapid results when compared to conven-tional culture, with results being availablewithin hours rather than days. Such rapidmethods may prove useful in cases whereearly diagnosis may alter patient manage-ment or treatment.

Since its discovery PCR has impacted onvirtually all areas of microbiology and inparticular has been used to detect microbialpathogens in a wide range of sample types.The first application of PCR for the specificdetection of C. jejuni and C. coli wasdescribed in 1992 [123]. The assay targetedthe flagellin A gene of C. jejuni and C. coliand was demonstrated to be specific forthese two species and successfully detected30–60 bacteria per PCR reaction in seededhuman faecal samples. This report alsodemonstrated the potential of the PCR-based methods to detect very low numbersof Campylobacter cells. However, complex

sample preparation methods and the use ofgel electrophoresis end-point detectionmethods, requiring manipulation of ampli-fication products following PCR cycling,hampered the transition of these methodsfrom research to routine microbiology labora-tories. Adaptation of PCR assays into a micro-plate hybridisation format or PCR-ELISAincreased the specificity and sensitivity ofdetection. Lawson et al. [71] developed apanel of PCR-ELISA assays which theyused in a large-scale survey of the detectionof Campylobacter species in human gastroen-teritis. The assays could detect and differen-tiate between C. jejuni, C. coli, C. upsaliensis,C. helveticus, C. fetus, C. hyointestinalis andC. lari with the PCR-ELISA results beingcompared with conventional culture meth-ods. The PCR-ELISA assays detectedcampylobacters in culture-negative faecalsamples and also more importantly, detectedmixed infections with more than one Campy-lobacter species. The assays did provideinformation on the identity and occurrenceof species that are not detected by culture,however the authors did note that PCR wasmore expensive and labour-intensive thanculture. The use of such assays may proveuseful in further large-scale epidemiologi-cal surveys of Campylobacter infection andprovide evidence of the role of Campylo-bacter species, other than C. jejuni andC. coli, in human disease.

The first report of a PCR assay for thedetection of campylobacters in foods wasmade by Giesendorf et al. [54] who describeda PCR assay for the rapid and sensitivedetection of Campylobacter species inchicken products. The assay was applied tothe detection of Campylobacter species inboth naturally contaminated and artificiallyinoculated samples of chicken skin follow-ing enrichment culture of the samples for18 h in Preston enrichment broth. The assaydemonstrated a limit of detection of 25 CFUof Campylobacter species per gram oftissue following the 18 h enrichment. Theuse of PCR for the detection of Campylo-bacter in foods is hampered by the rela-tively large sample size (25 g in most


routine test procedures) compared to thefinal template volume in the PCR assay(often 1–5 µL). For a PCR assay to replaceconventional culture methods, it must havea limit of detection sufficiently sensitive tobe able to detect a single Campylobactercell in 25 g food. In order to biologicallyamplify the numbers of cells present, manyPCR-based studies have utilised enrich-ment culture prior to application of the PCRassay. There have been many furtherreports of PCR assays for the detection ofcampylobacters in a range of sample typesincluding foods, environmental waters andother environmental samples. Althoughthese assays may be useful as an adjunct toenrichment culture, by reducing the totaltime of detection by two or more days, theyare still limited by inefficient sample prep-aration methods. Many PCR assays have alimit of detection of a single cell per reac-tion, however the inability to separate lownumbers of cells away from the samplematrix remains the “bottleneck” for the adop-tion of PCR-based methodologies in routinefood microbiology testing laboratories.Specific and sensitive methods are requiredto separate the target cells away from thesample matrix in a form amenable for PCR-based detection. In a recent study, paramag-netic beads were utilised as a method forisolating Campylobacter from chicken cecalcontents and faecal samples, prior to PCR[139]. The beads initially bound to the cellsin the liquid sample matrix and then lysisbuffer was added to lyse the cells releasingthe DNA, which then also bound to thebeads. The DNA was then washed and usedas template in the PCR assay. This proce-dure may prove useful in food testing labo-ratories, however further studies are requiredto validate this approach for food sampletesting.

The introduction of real-time PCR meth-ods have facilitated the development ofquantitative PCR assays for the detection ofCampylobacter in foods [145], milk andenvironmental waters [194]. The assaysdemonstrated a range of quantitation over6 orders of magnitude with the results cor-

relating closely with culture. The quantita-tive detection of Campylobacter directly inraw-meat rinse fluid samples was also dem-onstrated however the limit of detectionwas compromised by the presence of PCRinhibitors and the low numbers of cellspresent (Sails et al., unpublished data). Theuse of sensitive, quantitative PCR methodsfor the detection of Campylobacter duringfood processing could be used to determinepoints in the food production process wherecontamination occurs and where controlscould be introduced to reduce or eliminateCampylobacter from retail food products,thereby reducing the risk to the consumer.

The ultimate goal of nucleic acid baseddetection methods is to facilitate directdetection of pathogens in food samples with-out the need for enrichment culture. Thiswould permit more rapid detection of path-ogens, thereby reducing the time of detec-tion to hours, rather than days. In order todetermine the viability of the detected path-ogen, the assay must target a cellular proc-ess or molecule, which has been shown tobe associated with bacterial viability underall conditions tested. Conventional PCRmethods detect chromosomal gene sequences,which can be present in non-viable cells.Therefore, direct detection by conventionalPCR cannot determine the viability of thedetected cells somewhat limiting the use-fulness of such methods in food microbiol-ogy testing. Detection of viable cells usingmessenger RNA (mRNA) as the target forreverse transcriptase PCR (RT-PCR) hasbeen investigated for several microbialpathogens including C. jejuni [144]. TheRT-PCR assay was demonstrated to differ-entiate between viable and heat-killed cellsof C. jejuni, however the method of killingand post-treatment holding conditions didinfluence the rate of mRNA degradation inthe cells. Further studies are required toinvestigate the effect of different killingmethods and post–treatment holding condi-tions to determine the factors which influ-ence the rate of mRNA degradation in deadcells. This will allow the above factors to be

Campylobacter 373

investigated and the results related to foodprocessing methods.

Campylobacter detection methods haveimproved significantly since the initial iso-lation of campylobacters using membranefiltration and non-selective media in theearly 1970s. Improvements in molecularmethods have facilitated the developmentof nucleic acid-based detection methodswhich are more rapid, sensitive and spe-cific. In the future, improvements in sampleextraction methods allowing more sensitivedetection of cells by PCR will facilitate theuptake of these methods by microbiologylaboratories. Eventually, biological growthor amplification in vitro may be replacedwith DNA amplification, with culture mediabeing replaced by PCR reagents and theincubator being replaced by the thermalcycler.

9. CONCLUSIONS

The past three decades have witnessedthe rise of Campylobacter enteritis in manfrom virtual obscurity to notoriety, withpresent isolation rates superseding those ofother enteric pathogens such as Salmonellaspp. and Shigella spp. in most developedcountries. Unlike the salmonellae and otherenteric pathogens, the majority (ca. 99%) ofclinical reports concerning Campylobacterare sporadic and Campylobacter enteritisoutbreaks are rare. The lack of well-devel-oped typing schemes has hindered the epi-demiological investigations seeking naturalreservoirs of the organism and modes oftransmission from these sources to man.Only about 15% of clinical isolates areidentified to species level thus making epi-demiological investigations extremely dif-ficult to perform. Since the development ofmore sophisticated isolation techniques,the true disease potential of these organismshas become apparent and today campylo-bacteriosis is regarded as a zoonosis, whichis capable of being transmitted to man by awide range of domestic animals. Presently,the laboratory isolation of these organisms

has become routine from both clinical aswell as from environmental specimens andalthough relatively complicated to perform,routine isolation has been carried out withsuccess for this past 20 years or so.

Campylobacter spp. are the most com-mon cause of acute gastroenteritis in thedeveloped world. Thermophilic campylo-bacters, i.e. those Campylobacter spp. whichare able to proliferate at 42 °C, particularlyC. jejuni, C. coli and C. lari, are of partic-ular interest to the food industry, as thesecampylobacters form the natural microfloraof the gastrointestinal tract of severaldomestic and pet animals including poultry.Although campylobacters are the most com-mon cause of acute human enteritis, theirroutes of infection and transmission to manare still not fully understood. Further workis still required to find the source(s) of theseorganisms of major public health concern.

ACKNOWLEDGEMENTS

All authors are listed in alphabetical order,with the exception of the corresponding author,as each author played an equal role in the prep-aration of this manuscript. J.E. Moore and D.A.McDowell are funded by the Research & Devel-opment Office, Department of Health & PublicSafety, Northern Ireland (Infectious Disease –Recognised Research Group (RRG) 9.9).

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