Pathogens of the gastrointestinal tract

Dr. Dóra SzabóSemmelweis University

Institute of Medical Microbiology

Gram-negative facultative anaerobic rods(Positive glucose fermentation)

Oxidase positive Oxidase negative

Vibrionaceae Aeromonadaceae

Vibrio Aeromonas

Enterobacteriaceae

EscherichiaKlebsiella

EnterobacterProteusSerratia

ProvidenciaMorganella

EdwardsiellaCitrobacter

Hafnia

SalmonellaShigellaYersinia

Facultative pathogenic

Obligate pathogenic

Plesiomonas

Enterobacteriaceae

Morphology and General Characteristics

– Gram-negative, non-sporing, rod shaped bacteria

– Oxidase –

– Ferment glucose and may or may not produce gas in the process (aerogenic vs anaerogenic)

Differentiation– biochemical reactions

– differences in antigenic structure

Slideagglutination!

Enterobacteriaceae

– Member of the normal GI tract

– GI tract of human and animal

– Pathogen species

Enteral pathogens

Extraintestinal pathogens

More than 15 species:

– Escherichia, Shigella, Edwardsiella, Salmonella, Citrobacter, Klebsiella, Enterobacter, Hafnia, Serratia, Proteus, Providencia, Morganella, Yersinia, Erwinia, Pectinobacterium

Escherichia coli

Member of the normal GI tract

Extraintestinal infection urinary tract infections

Neonatal meningitis –strains with the K1 capsular antigen.

Peritonitis, cholecystitis

Nosocomial infections

Intestinal infections - gastroenteritis

E. coli intestinal infections

Gastroenteritis – there are several distinct types of E. coli that are involved in different types of gastroenteritis:

–enterotoxigenic E. coli (ETEC),

–enteroinvasive E. coli (EIEC),

–enteropathogenic E. coli (EPEC) ,

– enteroaggregative E. coli (EAEC), and

– enterohemorrhagic E. coli (EHEC).

Summary of E.coli strains that cause gastroenteritis.

E. coli gastroenteritisenteroheamorrhagic E. coli (EHEC).

EHEC – The organism attaches via pili to the intestinal mucosa and liberates the shiga-like toxin.

Symptoms: watery diarrhea,bloody diarrheawithout pus and crampy abdominal pain with no fever or a low-grade fever

This may progress to hemolytic-uremic syndromethat is characterized by low platelet count, hemolytic anemia, and kidney failure.

This is most often caused by serotypes O157:H7.

ZOONOSIS, Hamburgers!

Gram-negative facultative anaerobic rods(Positive glucose fermentation)

Oxidase positive Oxidase negative

Vibrionaceae Aeromonadaceae

Vibrio Aeromonas

Enterobacteriaceae

EscherichiaKlebsiella

EnterobacterProteusSerratia

ProvidenciaMorganella

EdwardsiellaCitrobacter

Hafnia

SalmonellaShigellaYersinia

Facultative pathogenic

Obligate pathogenic

Plesiomonas

SALMONELLA

SALMONELLA SPP.

Gram-negative

motile rods, peritrich flagella

Facultative anaerobic

O antigens

H (flagella) antigens

Salmonella typhi also has a Vi antigen which is a capsular antigen.

Biochemical properties:

H2S production

Lactose negative, Urease negative, Indol negative

Salmonella enteritidis

Salmonella typhimurium

ZOONOZIS

Salmonella typhiS. paratyphi A, B, and C

Clinical significance

GASTROENTERITIS, SALMONELLOSIS

ENTERIC FEVER

GASTROENTERITIS, SALMONELLOSIS

SALMONELLOSIS - Pathogenesis

SALMONELLOSIS - Clinical picture I.

Symptoms generally appear 18 to 36 hours after exposure, but they can occur as quickly as 12 hours or as long as 72 hours after exposure.

GASTROENTERITIS, but can be: – dizziness– vomiting– Abdominal pain

The symptoms can be similar to dysentery

The symptoms moderate in a few days – spontan recovery in a week

After recovery carrier status can occur– That patient can a source of infection later

SALMONELLOSIS - Clinical picture I.

Transient bacteraemia can occur

Permanent bacteraemia, sepsis, meningitis: – Very old patient

– Very young patient

– Immunsuppressed and AIDS patient

Focal infections can occur – lung

– brain

– in atherosclerotic plaque of aorta

– prothesis

SALMONELLOSIS - Epidemiology One of the most common cause of

foodpoisoning – More than 15 000 known cases per year in Hungary– 1-10% of the real cases – Increasing incidence

Reservoirs: – Chicken –and duck eggs – Chicken and swine– The feces of some pets,

especially those with diarrhea– Reptiles: turtles, lizards, snakes

Insufficient heat treatment is necessary!!

SALMONELLOSISMicrobiological diagnosis I.

Clinical specimen:faeces : positive from first week, and may remain positive for several weeksfood leftover

Microscopic examination:Direct smear has no value in the diagnosis.

Culture:Samples are inoculated onto brilliant green and/or bismuth sulphiteselective media.

Identification:Biochemical identification, slide agglutination (O and H agglutination

SALMONELLOSIS - Therapy

1. Water and electrolytes replacement

2. The vast majority of enterocolitis cases do not require an antibiotic treatment. After antibiotic treatment carrier status occurs more frequently.

Antimicrobial treatment of Salmonella infection of neonates, as well as invasive salmonella infections is important.– ampicillin – sulfomethoxazole + trimethoprim– fluoroquinolones – 3rd generation cephalosporinsAntibiotic susceptibility tests are important

ENTERIC FEVER

ENTERIC FEVER

THYPHOID FEVER

caused by S. typhi ,

PARATHYPHOID FEVER

caused by S. paratyphi A, B and C milder disease

The source is always human!!

ENTERIC FEVER - Pathogenesis

ENTERIC FEVER - Clinical picture

First week: The disease classically presents with step-ladder fashion rise in temperature (40 - 41°C) over 4 to 5 days, accompanied by headache, vague abdominal pain, and constipation.

Second week: Between the 7 th -10 th day of illness, mild hepato-splenomegally occurs in majority of patients. Relative bradycardia may occur and rose-spots may be seen.

Third week: The patient will appear in the "typhoid state" which is a state of prolonged apathy, toxaemia, delirium, disorientation and/or coma. Diarrhoea will then become apparent. If left untreated by this time, there is a high risk (5-10%) of intestinal hemorrhage and perforation.

Rare complications:Typhoid hepatitis, Empyema, Osteomyelitis, Cystitis and Psychosis.

2-5% patients may become Gall-bladder carriers

Typhoid fever a: petechia, b: Peyer plaque and necrosis of the ileum c, d: perforation of the Peyer-plaque

Fig. 4.37 Typhoid fever. Numerous ulcers of the small intestine

overlying hyperplastic lymphoid follicles (Peyer’s patches). By courtesy

of Dr. J. Newman.

Rose spots on the chest and abdomen of patients with typhoid fever due to the bacterium Salmonella typhi.

ENTERIC FEVER Microbiological diagnosis I.

Clinical specimen:faeces: positive from the second or third weeks (45-75% positive)urine : positive from the second week (45-75% positive)bile, bone marrow aspirate (85-95% positive)blood for blood-culture : often positive (70-80%) in the first weekCulture: Samples are inoculated onto brilliant green and/or bismuth sulphiteselective media.

Blood serology:=> Gruber-Widal reaction (Widal`s type tube agglutination): (Ag = 'H' as well as 'O' antigens of the laboratory strain of S. typhi) to show presence and establish titre of specific antibodies in the patient’s serum.

Biochemical identification: (refer to flow charts) Lactose (-), dextrose fermentation w/o gas formation, H2S (+)

Serological identification:Slide agglutination with specific antibodies to show presence of S. typhi cells in the culture.

Blood serology:=> Gruber-Widal reaction (Widal`s type tube agglutination): (Ag = 'H' as well as 'O' antigens of the laboratory strain of S. typhi) to show presence and establish titre of specific antibodies in the patient’sserum. High titre of antibody to O antigen > 1:640 is suggestive but

not specific.

ENTERIC FEVER Microbiological diagnosis II.

TreatmentAntibiotics according to susceptibility tests: S. typhi strains are usually susceptible to– ampicillin,

– sulfomethoxazole + trimethoprim,

– 3rd generation cephalosporins.

Prevention– Specific sanitary measures and control of chronic carriers.

– VaccinationInjectable Typhoid vaccine

(TYPHIM –Vi,TYPHIVAX)The live oral vaccine (TYPHORAL)TAB vaccine

“Carriers”3 % of survivors of typhoid become permanent carriers, harbouring the organisms in the gallbladder, biliary tract or urinary tract.

ENTERIC FEVER Treatment and prevention

In 1906, Irish immigrant

Mary Mallon worked as a

cook in the Oyster Bay summer

home of New York banker

Charles Henry Warren and

his family. By the end of the

summer, six members of the

household had contracted typhoid fever. Mallon, while immune herself to the disease, was its carrier. For three years, she was isolatedon North Brother Island, near Rikers Island, earning the nickname "Typhoid Mary." Instructed not to cook for others upon her release, she nevertheless changed her name and became a cook at a maternity hospital in Manhattan. At least 25 staff members contracted typhoid. "Typhoid Mary" returned to North Brother Island, where she lived alone for 23 years, until her death in 1938. She died of a stroke after 23 years in quarantine.

Mary Mallon

(wearing glasses)

photographed

with

bacteriologist

Emma Sherman

on North Brother

Island in 1931 or

1932, over 15

years after she

had been

quarantined there

permanently.

SHIGELLA

SHIGELLA GENUS

Contains four species that differ antigenically based on antigen and to a lesser extent, biochemically.

Serogroup A: S. dysenteriae (12 serotypes)

Serogroup B: S. flexneri (6 serotypes)

Serogroup C: S. boydii (23 serotypes)

Serogroup D: S. sonnei (1 serotype)

OBLIGATE HUMAN PATHOGEN

VIRULENCE FACTORS OF SHIGELLA

Shiga toxin– chromosomally encoded– role in the ulceration of the intestinal mucosa and in the death– produced by S. dysenteriae and in smaller amounts by S. flexneri and S.

sonnei. – Effect the capillar endothel

– B-subunit binds to Gb3 glycolipid receptor

– A-subunit inhibit the proteIn synthesis binding by inactivating the 60S

ribosomal subunit of aminoacyl-transfer RNA

Iron capturing ability

Other toxins: neurotoxic, cytotoxic and enterotoxic

SHIGELLOSIS - Pathomechanism I.

SHIGELLOSIS - Pathomechanism II.

Shigella penetrate the mucosa and epithelial

cells of colon, but most commonly in the

rectum and ampulla. No before terminal

ileum.

Lead to inflammation of the colon, and necrosis

of the colonic epithelium.

The resulting colitis and ulceration of the

mucosa result in bloody, mucoid stools, and/or

febrile diarrhea

SHIGELLOSIS– Clinical picture

There is an incubation of 1-7 days

Fever, cramping, abdominal pain, and diarrhea (due to the toxin) for 1-3 days.

This may be followed by frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa).

Complictions:– HUS,

– reactive arthritis

– Reiter-syndrome

The severity of the disease depends upon the species one is infected with.

– S. dysenteria (producing Shiga toxin) is the most pathogenic followed by S. flexneri, S. sonnei and S. boydii.

Colon in dysenteriae

Shigellosis. Sigmoidiscopic view of colonic mucosa in a mild case of infection due to S. flexneri. Note the thin whitish exsudate, which is made up of fibrin and polymorphonuclear leucocytes.

Shigellosis. Sigmoidiscopic view of colonic mucosa in a fatal case of infection with S. dysenteriae type 1 showing extensive pseudomembranous colitis.

SHIGELLOSIS – Epidemiology

Transmission is via the fecal-oral route, but by food and by wateras well.

The infective dose required to cause infection is very low (10-200 organisms).„Dirty hand disease”

Shigella dysenteriea 1: Asia, Africa, Middle-America

Shigella sonnei: US, Europe

SHIGELLOSISMicrobiological diagnosis

Clinical specimen: faeces, food leftover

Culture: Samples are inoculated on selective-differentiating medias.-dezoxycholate citrate agar

- eosin methylen blue agar

Biochemical identification, slide agglutionation for O antigen

Positive Serény test. Keratoconjunctivitis

in the rabbit produced by the instillation

of shigella microorganism

SHIGELLOSIS-Treatment and prevention

Treatment– Water and electrolytes replacement

– Antimicrobial therapy– Sulfonamides are commonly used as are streptomycin,

tetracycline, ampicillin, and chloramphenicol.

– Resistant strains are becoming increasingly common, so sensitivity testing is required.

Prevention– Vaccination

Live attenuated vaccine

Subunit vaccines

Yersinia

– Three species are important pathogens in human

Yersinia pestis – causes plague

Yersinia enterocolitica – enteropathogenic

Yersinia pseudotuberculosis – enteropathogenic

Yersinia enterocoliticaY. pseudotuberculosis

– Infection with contaminated food or water– fever and abdominal pain– Y. enterocolitica *watery diaorrhea

– Invade the intestinal epithelium by invasion of M cells – penetrate into the underlying lymphoid tissue causing

inflammation– extreme pain associated with the infections (resembles

acute appendicitis) drain into adjacent mesenteric lymph nodes, causing mesenteric lymphadenitis

– Reactive arthritis may occur in some people following Y. enterocoliticainfection. It is thought to be due to cross reacting T cells or antibodies that attack

the joints

– Y. enterocolitica is a common cause of human disease, whereas, Y. pseudotuberculosis is mainly a disease of other animals.

Gram-negative facultative anaerobic rods(Positive glucose fermentation)

Oxidase positive Oxidase negative

Vibrionaceae Aeromonadaceae

Vibrio Aeromonas

Enterobacteriaceae

EscherichiaKlebsiella

EnterobacterProteusSerratia

ProvidenciaMorganella

EdwardsiellaCitrobacter

Hafnia

SalmonellaShigellaYersinia

Facultative pathogenic

Obligate pathogenic

Plesiomonas

Vibrionaceae

Vibrio spp.

– V. cholerae

– V. paraheamolyticus

Aeromonas spp.

Plesiomonas spp.

Photobacterium spp.

V. cholerae Classification Scheme

I define Vibrios!

I’m an

O1 or O139 Strain

www.forth.go.jp/tourist/ panf/cholerae.html

NON-TOXIGENIC TOXIGENIC

I may not be O1,

Or O139!(but I can still

stir up trouble)

Classification Scheme

Toxigenic V. cholerae

O1Division into 2 biotypes

inaba ogawa hikojima

A & B(A little C) Antigens

A & C

O139

A, B, C

Each O1 biotype can have 3 serotypes

Classical El Tor

Designed using information presented in review by NS Crowcroft. 1994. Cholera: Current Epidemiology. The

Communicable Disease Report. 4(13): R158-R163.

Division into ribotypes

Division into 2 epidemic serotypes

Biochemical Properties

Gram-negative

Straight or curved rods

Oxidase positive

Fermentative and oxidative in metabolism

Pathogenesis

Transmitted by the fecal-oral route

Adheres and colonizes to the small bowel– Toxin co-regulated pili

(TCP)

Secretes the choleraeenterotoxin (CT)

Causes an increase in cAMP

Pathogenesis

The organism never invades the cell!!

Cholera toxin (AB toxin) will increase the cAMP level

The increased cAMP causes:

– Mucosal cells to pump large amounts of Cl- into the intestine

– Water, Na+, and other electrolytes follow due to the osmotic and electrical gradients

– Diarrhea results, leading to the classic symptoms of cholerae

Clinical Manifestations

www.who.int/entity/water_sanitation_health/dwq/en/admicrob6.pdf

Modes of Transmission

Water (infectious dose = 109)

Food (infectious dose = 103)

Person-to-person

The 19th-century illustration depicting the spirit of death at a pump was taken from

http://news.nationalgeographic.com/news/2004/06/0614_040614_tvcholera.html

Diagnosis

Severe watery diarrhea

– “Rice-water stool”

Dehydration

Loss of urine production

Shock

A wet mount of liquid stool can be examined microscopically

cholerae cot’s

Microbiological detection

Microbiological culture-based methods using fecal or water samples– TCBS (thiosulphate citrate bile salts) media

Rapid Tests– Dark-field microscopy

– Rapid immunoassays

– Molecular methods - PCR

and DNA probes

Cholera Treatment

• Rehydration

• Parenteral

• Oral

• Antibiotic treatment not recommended!

• Short duration of illness

• Antibiotic resistance

• Limited gain from usage

Treatment: Oral Rehydration Salts (ORS)

• Reduces mortality from over 50% to less than 1%

• Packets of Oral Rehydration Salts• Distributed by WHO, UNICEF

• Dissolve in 1 L water

• NaCl, KCl, NaHCO3, glucose

Treatment: How ORS Works

• Na+ transport coupled to glucose transport in small intestine

• Glucose enables more efficient absorption of fluids and salts

• Potassium passively absorbed

479. Dehydrated patient before treatment

480. Rehydration – dehydrated patient after treatment

Vaccines

• Need localized mucosal immune response

• Oral Vaccine

• Not recommended• Travelers have very low risk of contracting disease: 1-2

cases per million international trips

• Not cost-effective to administer vaccines in endemic regions

• Brief and incomplete immunity

• Two types approved for humans:

• Killed whole-cell

• Live-attenuated

Thank you for the attention!