standardization of pulsed-field gel electrophoresis

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FOODBORNE PATHOGENS AND DISEASE Volume 3, Number 1, 2006 © Mary Ann Liebert, Inc. Standardization of Pulsed-Field Gel Electrophoresis Protocols for the Subtyping of Escherichia coli O157:H7, Salmonella, and Shigella for PulseNet EFRAIN M. RIBOT, 1 M.A. FAIR, 1 R. GAUTOM, 2 D.N. CAMERON, 1 S.B. HUNTER, 1 B. SWAMINATHAN, 1 and TIMOTHY J. BARRETT 1 ABSTRACT Standardized rapid pulsed-field gel electrophoresis (PFGE) protocols for the subtyping of Escherichia coli O157:H7, Salmonella serotypes, and Shigella species are described. These protocols are used by laboratories in PulseNet, a network of state and local health departments, and other public health laboratories that perform real-time PFGE subtyping of these bacterial foodborne pathogens for surveillance and outbreak investigations. Development and standardization of these protocols consisted of a thorough optimization of reagents and reaction conditions to en- sure that the protocols yielded consistent results and high-quality PFGE pattern data in all the PulseNet partici- pating laboratories. These rapid PFGE protocols are based on the original 3–4-day standardized procedure devel- oped at Centers for Disease Control and Prevention that was validated in 1996 and 1997 by eight independent laboratories. By using these rapid standardized PFGE protocols, PulseNet laboratories are able to subtype food- borne pathogens in approximately 24 h, allowing for the early detection of foodborne disease case clusters and often aiding in the identification of the source responsible for the infections. 59 INTRODUCTION T HE GLOBALIZATION of food markets and changes in food processing and distribu- tion practices, where a contaminated food product could reach consumers across city, state, or country borders, have contributed to the increase in the number of multi-state and multi-country outbreaks of foodborne illness (Barrett et al., 1994; Campbell et al., 2001; CDC, 1998, 1999). The increased occurrence of multi- locality foodborne outbreaks presents a new and complicated challenge for epidemiologists in the United States and abroad. Perhaps the biggest challenge is the development of strate- gies that would allow for the rapid identifica- tion of clusters of illness and, in particular, outbreak-related cases that are dispersed throughout a larger region in order to prevent additional infections from occurring (Tauxe, 1997). The development and application of epi- demiologically relevant molecular subtyping techniques and the availability of highly so- phisticated computer software for data analy- sis have increased the role laboratories play in the detection of clusters of illness and investi- gation of outbreaks of bacterial infections. De- spite these advances, different laboratories do not always use the same methods for subtyp- ing, making inter-laboratory comparisons ex- tremely difficult, if not impossible. Even when the same method is used, minor differences in the protocol conditions or parameters often re- sult in data that are not comparable (Bolton et al., 1996; van Belkum et al., 1995; van Belkum, 1998). The integration of these tools coupled 1 Centers for Disease Control and Prevention, Atlanta, Georgia. 2 Washington State Department of Health, Public Health Laboratories, Shoreline, Washington.

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FOODBORNE PATHOGENS AND DISEASEVolume 3, Number 1, 2006© Mary Ann Liebert, Inc.

Standardization of Pulsed-Field Gel ElectrophoresisProtocols for the Subtyping of Escherichia coli O157:H7,

Salmonella, and Shigella for PulseNet

EFRAIN M. RIBOT,1 M.A. FAIR,1 R. GAUTOM,2 D.N. CAMERON,1 S.B. HUNTER,1B. SWAMINATHAN,1 and TIMOTHY J. BARRETT1

ABSTRACT

Standardized rapid pulsed-field gel electrophoresis (PFGE) protocols for the subtyping of Escherichia coli O157:H7,Salmonella serotypes, and Shigella species are described. These protocols are used by laboratories in PulseNet, anetwork of state and local health departments, and other public health laboratories that perform real-time PFGEsubtyping of these bacterial foodborne pathogens for surveillance and outbreak investigations. Development andstandardization of these protocols consisted of a thorough optimization of reagents and reaction conditions to en-sure that the protocols yielded consistent results and high-quality PFGE pattern data in all the PulseNet partici-pating laboratories. These rapid PFGE protocols are based on the original 3–4-day standardized procedure devel-oped at Centers for Disease Control and Prevention that was validated in 1996 and 1997 by eight independentlaboratories. By using these rapid standardized PFGE protocols, PulseNet laboratories are able to subtype food-borne pathogens in approximately 24 h, allowing for the early detection of foodborne disease case clusters andoften aiding in the identification of the source responsible for the infections.

59

INTRODUCTION

THE GLOBALIZATION of food markets andchanges in food processing and distribu-

tion practices, where a contaminated foodproduct could reach consumers across city,state, or country borders, have contributed tothe increase in the number of multi-state andmulti-country outbreaks of foodborne illness(Barrett et al., 1994; Campbell et al., 2001; CDC,1998, 1999). The increased occurrence of multi-locality foodborne outbreaks presents a newand complicated challenge for epidemiologistsin the United States and abroad. Perhaps thebiggest challenge is the development of strate-gies that would allow for the rapid identifica-tion of clusters of illness and, in particular,outbreak-related cases that are dispersed

throughout a larger region in order to preventadditional infections from occurring (Tauxe,1997). The development and application of epi-demiologically relevant molecular subtypingtechniques and the availability of highly so-phisticated computer software for data analy-sis have increased the role laboratories play inthe detection of clusters of illness and investi-gation of outbreaks of bacterial infections. De-spite these advances, different laboratories donot always use the same methods for subtyp-ing, making inter-laboratory comparisons ex-tremely difficult, if not impossible. Even whenthe same method is used, minor differences inthe protocol conditions or parameters often re-sult in data that are not comparable (Bolton etal., 1996; van Belkum et al., 1995; van Belkum,1998). The integration of these tools coupled

1Centers for Disease Control and Prevention, Atlanta, Georgia.2Washington State Department of Health, Public Health Laboratories, Shoreline, Washington.

with advances in the information technologiesarena has enabled us to rapidly recognize clus-ters of illness that would have previously goneundetected, especially those linked to a com-mon source (Chan et al., 2002; Cummings et al.,2001; Proctor et al., 2001).

A wide array of DNA fingerprinting meth-ods have been used for the purpose of subtyp-ing bacteria (Holmberg et al., 1984; Maslow etal., 1993; Olive and Bean, 1999). Restrictionfragment length polymorphism (RFLP) is oneof the most frequently used molecular subtyp-ing tools in epidemiologic investigations.While there are different approaches to RFLP,pulsed-field gel electrophoresis (PFGE) hasbeen shown to be a reliable and highly dis-criminating method for subtyping foodbornepathogens and other bacteria (Barrett et al.,1994; Swaminathan et al., 2001; Streulens et al.,2001; Georing, 2004). Even though PFGE is cur-rently considered the “gold standard” for thesubtyping of foodborne bacteria, its usefulnesshas been limited by reproducibility problemsand the inability to compare fingerprint dataobtained in different laboratories. These intra-and interlaboratory data compatibility issuescan be overcome by using highly standardizedlaboratory protocols for generating and ana-lyzing data. This was the original goal ofPulseNet, the molecular subtyping-based sur-veillance system for foodborne bacterial dis-eases, which was initiated by the Centers forDisease Control and Prevention (CDC) in 1996(Swaminathan et al., 2001). PFGE was selectedas the molecular subtyping method for food-borne bacteria after its utility for outbreak in-vestigations was convincingly demonstrated ina study of isolates from the E. coli O157:H7 out-break in the western United States in 1993 (Bar-rett et al., 1994). Implementation of PFGE intoPulseNet was preceded by a protocol develop-ment program charged with the responsibilityof standardizing the PFGE methodology aswell, as the data analysis system, to ensure thatthe data generated by different laboratorieswas comparable and of the highest quality pos-sible. Data reproducibility and comparabilityare paramount in the successful implementa-tion of any decentralized molecular subtypingsystem, such as PulseNet, independently of themethod used.

The use of rapid standardized PFGE proto-cols, analysis parameters and nomenclature,and the ability to exchange information in real-time via the internet are at the center ofPulseNet’s continued success (Swaminathan etal., 2001; Gerner-Smidt et al., 2005). Here, wedescribe rapid (24–28 h) standardized PFGEprotocols being used by PulseNet laboratoriestoday along with comments on those steps thatare particularly critical for the successful im-plementation of these protocols in laboratorieswith different levels of experience and re-sources.

MATERIALS AND METHODS

Rapid standardized PulseNet PFGE protocol forE. coli O157:H7, Salmonella, and Shigella species

Bacterial strains. Bacteria were grown onTrypticase soy agar plates with 5% sheep blood(TSA-SB; Becton Dickinson and Company,Sparks, MD) at 37°C for 14–16 h. All isolateswere identified and serotyped using standardprocedures (Ewing, 1986).

PFGE plug preparation. Cell suspensions wereprepared by removing cells from the plate sur-face with a sterile cotton or polyester fiber ap-plicator swab that has been moistened withsterile Cell Suspension Buffer (CSB, 100 mMTris, 100 mM EDTA [pH 8.0]) and transferringthem to tubes (Falcon 2057, 12 � 75 mm; Bec-ton Dickinson, Franklin Lakes, NJ) containing2 mL of CSB. The concentration of each cell sus-pension was adjusted to a turbidity reading of0.48–0.52 on the digital output of a MicroscanTurbidity Meter (Dade Behring, Inc., Deerfield,IL). This corresponds to absorbance values ofapproximately 1.3–1.4 measured at a wave-length of 610 nm with a spectrophotometer(Shimadzu Corp., Kyoto, Japan) and transmit-tance values of approximately 15% when usinga Vitek colorimeter (bioMérieux, Durham, NC).

A 400-�L aliquot of each adjusted cell sus-pension was transferred to a sterile microcen-trifuge tube containing 20 �L of proteinase K(20 mg/mL stock; Amresco, Solon, OH; Invit-rogen, Carlsbad, CA) and mixed gently by tap-

RIBOT ET AL.60

ping a capped tube on the palm of the hand orflicking it several times with fingers. Alterna-tively, the proteinase K can be added directlyto each cell suspension after they have beenaliquoted into their respective tubes. Theagarose used to make the plugs consists of 1%SeaKem Gold agarose (SKG, Cambrex, Rock-land, ME) and 1% sodium dodecyl sulfate(SDS; Roche Diagnostics Corp., Indianapolis,IN) prepared in Tris EDTA buffer (TE; 10 mMTris, 1 mM EDTA [pH 8.0]). The agarose mix-ture was thoroughly melted in a microwaveand allowed to equilibrate for 15 min in a54–56°C water bath. Four hundred microlitersof the equilibrated agarose mixture wereadded to each cell suspension and mixed gen-tly by pipetting up and down two to threetimes before immediately dispensing into thewells of reusable or disposable PFGE plugmolds (Bio-Rad, Hercules, CA). The plugswere allowed to solidify at room temperaturefor 5–10 min or at 4°C for 5 min. The plugs arethen removed from the molds and placed in a50-mL polypropylene conical tube (Blue-Max™, Becton Dickinson, Franklin Lakes, NJ)containing 5 mL of Cell Lysis Buffer (CLB; 50mM Tris, 50 mM EDTA [pH 8.0]; 1% Sarcosyl[Sigma, St. Louis, MO]; 0.1 mg/mL proteinaseK). The samples were incubated in a 54°Cshaking water bath or orbital shaking incuba-tor for 1.5–2 h with constant and vigorous ag-itation (150–175 rpm).

The tubes were removed from the water bathor incubator and the lysis buffer is discarded.The plugs can be quickly rinsed once with 10mL of sterile reagent grade water (type 1) to re-move the residual lysis buffer coating the plugsand the inside walls of the tube (this is an op-tional step). The plugs were then washed twotimes with 10–15 mL of sterile type 1 water(pre-heated to 50°C) in a 50°C water bath orshaker incubator for 10–15 min with constantagitation. This was followed by four washeswith 10–15 mL of sterile TE buffer (TE; 10 mMTris, 1 mM EDTA [pH 8.0]), pre-heated to 50°Cas described above. After the last wash, 5 mLof sterile TE buffer (room temperature) wereadded to each tube to serve as storage mediafor the plugs. The plugs were restricted imme-diately or stored in TE buffer at 4°C untilneeded.

Restriction digestion with XbaI. Slices approx-imately 2-mm-wide were cut from each of theplugs with a single edge razor blade or scalpeland placed in a sterile microcentrifuge tube thatcontains 200 �L of a 1� dilution of the appro-priate restriction buffer for the enzyme. Threeto four slices of the plug of the DNA size stan-dard strain (Salmonella ser. Braenderup H9812;Hunter et al., 2004) were cut and immersed in the appropriate restriction buffer solution in microcentrifuge tubes as described above.Three plug slices of the standard strain areneeded for 10-well gels and four for 15-wellgels. The standards and test samples were in-cubated in a 37°C water bath for 5–10 min. The1� restriction buffer mixture was replacedwith 200 �L of XbaI restriction enzyme mixture(40–50 U/slice; Roche) and incubated for 2 h at37°C. After incubation, the restriction mixturewas replaced with 200 �L of 0.5� Tris borateEDTA (TBE; prepared from 10� TBE contain-ing 0.89 M Tris borate, 0.02 M EDTA [pH 8.3];Sigma-Aldrich Co., St. Louis, MO) and allowedto stand for 5 min to saturate the plug sliceswith electrophoresis running buffer. Thesesame restriction enzyme and conditions wereused for plugs containing DNA from Salmonellaand Shigella strains. Restriction of plugs sliceswith the secondary enzyme BlnI (isoschizomerof AvrII; Roche) was performed, when needed,using 30 units of enzyme per plug slice and in-cubating at 37°C for 2 h.

Electrophoresis conditions and casting of theagarose gel. The 1% SKG agarose gel was pre-pared using either a 10-well comb (Bio-Rad) inthe standard casting stand or 15-well comb inthe wide/long casting stand (Bio-Rad). Theuniversal size standard plug slices were loadedinto wells 1, 5, and 10 of a 1% SKG agarose gel,and the test samples were loaded in the re-maining wells. For the larger casting stand, theuniversal size standard plug slices were loadedin wells 1, 5, 10, and 15. Alternatively, restrictedplug slices were loaded directly on the comb,prior to casting the gel, by aligning the plugslices in the appropriate order on the loweredge of the comb teeth. Excess liquid was re-moved with a tissue, and the plug slices wereallowed to air dry for approximately 3–5 minbefore pouring the melted 1% SKG agarose

PROTOCOLS FOR SUBTYPING OF E. COLI, SALMONELLA, AND SHIGELLA 61

RIBOT ET AL.62

(equilibrated to 55–60°C). The comb was placedin the gel casting mold so that the teeth of thecomb and the plug slices are flush with the bot-tom of the casting mold. The gels were allowedto polymerize for approximately 30 min atroom temperature.

The E. coli O157:H7 electrophoresis condi-tions were determined originally by using theAuto Algorithm feature on the CHEF MapperXA System (Bio-Rad) set to resolve restrictionfragments in the range of 30–600 kb. The re-sulting electrophoresis conditions are as fol-lows: initial switch time value of 2.16 sec, finalswitch time of 54.17 sec at a gradient of 6 V/cmand an included angle of 120°. Depending onthe size of the gel, they are electrophoresed for18–19 h in 0.5� TBE (Sigma) at 14°C; however,the electrophoresis run time may vary fromlaboratory to laboratory and must be deter-mined empirically. These same electrophore-sis conditions and electrophoresis run time areused for PFGE of Shigella isolates. For Salmo-nella, which typically yields restriction frag-ments that are larger than those observed withE. coli O157:H7 and Shigella, the electrophore-sis conditions are modified slightly in order tooptimize the resolution of these fragments. Theelectrophoresis conditions for Salmonella are asfollows: initial switch time of 2.16 sec and a fi-nal switch time of 63.8 sec (based on a frag-ment range of 30–700 kb) and electrophoresisrun time of 18–19 h.

Size standard. In 2003, PulseNet implementedthe use of a “universal” size standard, DNAfrom a strain of Salmonella ser. BraenderupH9812 that is restricted with XbaI (Hunter etal., 2005). This strain currently used with all thebacteria tracked by PulseNet and has been de-posited with the American Type Culture Col-lection (ATCC) under the accession number,ATCC BAA-664.

Image acquisition. After the electrophoresiswas completed, the gels were stained with 400mL of ethidium bromide solution (40 �g/mL)for 20 min with gentle rocking or shaking. Thegels were then de-stained with �400 mL ofdeionized water for 15–20 min a total of threetimes by gentle rocking or shaking. The band-ing pattern was observed under ultraviolet

(UV) illumination and a digital image (that canbe converted to the TIFF format) of the PFGEpatterns is acquired using the Gel Doc system(Bio-Rad) following the saturation and inte-gration parameters recommended by the man-ufacturer. Digital images obtained with equip-ment from other manufacturers will also workprovided that they can provide IBM-compati-ble uncompressed TIFF images and resolutionof �768 � 640 pixels.

Analysis of TIFF images. Initially, analysis ofthe TIFF images was carried out using the Mo-lecular Analyst Fingerprinting Plus (Bio-Rad)using the Dice coefficient and UPGMA to gen-erate dendrograms. The analysis parametersused in the reproducibility study (validation)were based on 1.5–1.2% tolerance values. In2001, the BioNumerics software (AppliedMaths, Sint-Martens-Latem, Belgium) was in-troduced to PulseNet for analysis and genera-tion of dendrograms.

RESULTS AND DISCUSSION

Preparation of PFGE plugs

A cell suspension buffer (CSB) containing ahigh concentration of the chelating agent EDTA(100 mM) is used to harvest the cells from theBAPs in order to minimize potential endonu-clease activity that may occur before the actuallysis step is initiated. Standard TE buffer wasnot selected as a cell suspension buffer becauseof its poor osmotic properties that often re-sulted in premature lysis of cells and DNAdegradation (observed as smearing or highbackground in the resulting gels). Cell suspen-sions were adjusted to values (equivalent to 4–5McFarland Standard) that consistently yieldedDNA fragments of uniform intensity withinand between PFGE patterns. To prevent cell ly-sis prior to immobilizing the cells in agarose,the cell suspensions were mixed gently by tap-ping a capped tube on the palm of the hand orflicking it several times with fingers. Vortexingcell suspensions is not recommended becauseit can cause cell lysis, resulting in shearing ofthe DNA and PFGE patterns with high back-ground and faint restriction fragments in the

PROTOCOLS FOR SUBTYPING OF E. COLI, SALMONELLA, AND SHIGELLA 63

upper portion of the gels where the larger frag-ments are normally found. We observed thatthe addition of 1% SDS to the plug agarose improved the efficiency of the lysis step by saturating the plugs with a detergent prior toplacing them in the cell lysis buffer (which con-tains 1% sarcosyl). Similarly, proteinase K wasadded to the suspension prior to casting theplugs to expedite the process of reagent diffu-sion during the lysis step and to inactivate anyendonucleases that might be present.

Many previously published protocols rec-ommended the use of low-melting agarosesuch as Chromosomal Grade Agarose (Bio-Rad) or InCert agarose (Cambrex) in the plugspreparation. It is generally believed that thesofter and looser matrix created by this type ofagarose would allow for easier and faster ex-change of reagents between the plugs and thesurrounding lysis buffer solutions when com-pared with agarose with higher melting tem-perature. Unfortunately, the integrity of plugsmade with low-melting agaroses deterioratedduring the high temperature (54°C) lysis andwash steps outlined in this protocol. Evenwhen plugs appeared to be intact, the fragilenature of the low-melting agaroses made plugsextremely difficult to cut and handle withoutbreaking them. We incorporated SKG agarosein the plug preparation step to prevent thisfrom happening and to simplify the number ofreagents associated with this protocol.

Lysis of cells

Lysing cells for 1.5–2 h at 54°C resulted inoptimal release of DNA from all the strainstested. No difference was observed betweenintensity of the restriction fragments obtainedwith the rapid protocol and plugs made withthe 3–4-day version of the standardized PFGEprotocol (Fig. 1). The 3–4-day protocol calledfor overnight lysis in a water bath at 54°C withgentle agitation. This modification to the orig-inal protocol represents the most significantchange to the original protocol, allowing a con-siderable reduction in the time needed forcompletion of the PFGE process, so the lysis,washing and restriction steps, followed byloading and running of the gel could be donein 8–10 h, depending on the number of cultures

processed. The concentration of proteinase Kin the lysis buffer was reduced by a factor of10 from 1 to 0.1 mg/mL in the rapid protocol.This change did not compromise the efficiencyof the lysis step (data not shown).

Washing of agarose plugs

Washing the plugs six times at 50–54°C for10–15 min per wash is sufficient to remove celldebris, residual SDS, sarcosyl, and proteinaseK from the lysed plugs. This reduced theamount of time required to complete the wash-ing steps by approximately 50% when com-pared to the longer (3–4-day) protocol, whichcalled for six washes of 20–30 min each. It isimportant to wash the lysed agarose plugs wellbecause residual detergents or proteinase Kwill interfere with the restriction digestion reactions and result in PFGE results of poorquality.

Restriction digestion

We recommend the use of 40–50 units perplug slice of XbaI for a 2-h restriction to ensurethat full restriction digestion of the DNA wouldbe achieved consistently. Less enzyme (30 unitsper plug slice) is recommended when using therestriction enzyme BlnI (AvrII) to achieve fullrestriction of DNA within the 2-h incubationperiod. Restriction digestion with a second,and in some cases, a third enzyme (SpeI) oftenincreases the overall discriminatory power ofPFGE. We recommend that BlnI be used in sit-uations where there is more than one isolatewith indistinguishable XbaI patterns. If thePFGE patterns are different with the primaryenzyme (XbaI), restriction with the secondaryenzyme (BlnI) may not be necessary unlessthere is interest in obtaining information onpattern combinations. For instance, primaryand secondary enzyme pattern combinations,in combination with epidemiologic informa-tion, can help us determine discriminatorypower of new non-PFGE subtyping methods.The use of the tertiary enzyme, SpeI at 30–40units per plug slice, is recommended in situa-tions where the PFGE patterns obtained withboth XbaI and BlnI from two or more isolatesare indistinguishable from each other. By us-ing a secondary and tertiary enzyme, we can

determine if isolates are likely to be from a common source of contamination. The originalPulseNet PFGE protocol recommended pre-in-cubating the plug slices in two volumes of re-striction buffer for 15–30 min each before theremoving and adding the enzyme mixture; therestriction digestion was done at 37°C for 4–16h. Decreasing the incubation in the pre-wash toone time for 10–15 min and the restriction to 2 h helped to reduce the time required to dothe protocol by several hours. The gel couldthen be set up and electrophoresis begun thesame day that the test samples were restricted.

Most problems associated with partial re-striction of DNA are related to one or more ofthe following: poor lysis, inadequate washingof the plugs, inaccurate measurement ofreagents, poor mixing of the restriction mix-ture, improper storage or handling of the en-zyme and/or restriction buffer. Measuring er-rors can be minimized by preparing a mastermix of reagents needed for the total number ofsamples being analyzed in a gel. Once thereagents are placed in the tube, it is importantto mix well to ensure the enzyme is evenly dis-tributed in the solution. This can be done by in-verting the tube several times, tapping on theside of tube with palm of hand or by gentlyvortexing. Restriction digestion reagents mustbe kept on ice or cold tray at all times. Expos-ing the enzymes to ambient temperature mustbe avoided as it may reduce enzyme activity.

Electrophoresis conditions and casting of the agarose gel

SeaKem Gold agarose was chosen as the run-ning gel because of its high purity and shorterrun time compared to other products availableat the time, including the Pulsed-Field Certi-fied Agarose (Bio-Rad) used with the originalPulseNet standardized PFGE protocol for E.coli O157:H7. Decreasing the electrophoresisrun time from run times of 22–23 h to 18–19 hor less was one of the improvements that madethe development of a rapid PFGE protocol pos-sible. This was a significant accomplishmentbecause it provided PulseNet participating lab-oratories with the capacity to generate PFGEfingerprint data that could be reported to epi-demiologists earlier.

Since the length of the electrophoresis runcan vary slightly from one instrument to an-other, we recommend that each laboratory de-termine the optimal electrophoresis runningtime independently for each electrophoresisunit. This can be done by determining thelength of the electrophoresis run time neededfor the smallest visible bands in the S. Braen-derup H9812 size standard (�20.5 kb in size)to migrate within 1–1.5 cm from the bottomedge of the gel. This will help minimize varia-tions in the migration of the DNA fragmentsthat make up the PFGE pattern of the size stan-dard. This is important because the images ob-

RIBOT ET AL.64

FIG. 1. Pulsed-field gel electrophoresis (PFGE) images of Escherichia coli O157:H7 strains generated using the 3–4-day protocol (A) and the rapid (1-day) protocol (B). The standards are in lanes 1, 4, 7, and 10 in both gels, with Ashowing the E. coli G5244 size standard used from 1996 to 2002, and B showing the universal standard strain (S.Braenderup H9812), used since 2003. Pulsed-field certified agarose (1%) was used to prepare the gel in A. The gel inB was prepared with 1% SeaKem Gold agarose according to the directions stated above. The electrophoresis run timewas 21 and 18 h for A and B gels, respectively.

tained will be normalized using the sameglobal standard, an electronic image of thestandard strain, by all laboratories participat-ing in PulseNet. Allowing the gels to run forthe appropriate amount of time also ensuresoptimal fragment resolution, which is criticalfor successful analysis and inter-laboratorycomparison of the resulting patterns (Figs. 1and 2). The 18–19-h run time stated in the pro-tocol described here is based on the PFGEequipment used in our laboratories and is onlyintended as a reference point. Other factors, in-cluding TBE buffer formulations, quality of thewater used to make this buffer, pH, tempera-ture and flow rate of the buffer can affect theelectrophoresis run time.

CONCLUSION

The ideal molecular subtyping methodwould be 100% sensitive (epidemiologically related isolates share the same profile) and specific (epidemiologically unrelated isolatesare different). No currently available methodmeets all of these criteria. However, there aresome methods that provide high levels of sensitivity, specificity, and reproducibility.Among these, PFGE has established itself as the“gold standard” for subtyping foodborne bac-terial pathogens. Standardization of all thePulseNet PFGE protocols is achieved by care-

ful evaluation of the different parameters andconditions so that high quality gels are pro-duced consistently and reproducibly at CDCand in the different laboratories that currentlyparticipate in PulseNet. PulseNet protocols areaccorded “standardized” status only after theyhave been thoroughly evaluated and validatedin several laboratories at CDC and elsewhere.Since the PulseNet standardized PFGE proto-col for E. coli O157:H7 was developed with thepurpose of transferring it to state health de-partments and other public health agencies,special attention was given to the aspects of theprotocol that could affect the quality and thereproducibility of the data. The original 3–4-day standardized PFGE protocol for E. coliO157:H7 used from 1996 to early 1998, wasevaluated by multiple laboratories to demon-strate its robustness and reproducibility priorto it full implementation in the PulseNet sys-tem (Swaminathan et al., 2001).

Soon after the implementation of the 3–4-daystandardized PFGE protocol in PulseNet in1996, we recognized the need for a protocol thatcould be completed in a shorter period of time.The challenge was to develop a standardizedPFGE protocol that could be completed withina day (24–28 h) so that subtyping data wouldbe available to epidemiologists in a timely man-ner. In 1997, the Washington State Departmentof Health developed a rapid (1-day) PFGE pro-tocol for subtyping of a wide variety of gram

PROTOCOLS FOR SUBTYPING OF E. COLI, SALMONELLA, AND SHIGELLA 65

FIG. 2. Pulsed-field gel electrophoresis (PFGE) images of Salmonella (A) and Shigella (B) strains analyzed with therapid standardized protocol. Lanes 1, 5, 9, and 10 in A contain the XbaI pattern for universal size standard strain(H9812). The remaining lanes contain Salmonella test isolates restricted with XbaI (lanes 2, 3, and 4) and BlnI (lanes 6,7, and 8). B shows a Shigella gel containing the H9812 standard strain (lanes 1, 5, and 10). The remaining lanes showtypical Shigella sonnei PFGE patterns. Both gels were electrophoresed for 18 h.

negative bacteria (Gautom, 1997). CDC, in col-laboration with the Washington State Depart-ment of Health, worked towards the harmo-nization between this 1-day protocol and thealready established 3–4-day standardizedPFGE protocol used by all the PulseNet labo-ratories at that time. The quality of the PFGEpatterns produced and the discriminatorypower obtained with the 1-day standardizedPFGE protocol was the same or higher thanthose obtained with the 3–4-day standardizedprotocol. In 1998, PulseNet implemented therapid standardized PFGE protocol for the sub-typing of E. coli O157:H7. Shortly thereafter, itwas determined that this rapid standardizedprotocol could also be used for the subtypingof Salmonella and Shigella species. Since then,these protocols have been used by over 70PulseNet laboratories to successfully analyzethousands of isolates every year. These labora-tories routinely generate PFGE patterns, whichare submitted and compared with patterns inthe PulseNet National Database with the goalof identifying clusters of strains that have thesame PFGE pattern. This, in fact, is the best val-idation of the PulseNet standardized PFGEprotocols and the strongest evidence of the protocols’ robustness and reproducibility. Thestandardized PFGE protocol for E. coliO157:H7also served as the foundation to for thedevelopment of protocols for the PulseNet pro-tocols for Listeria monocytogenes (Graves andSwaminathan, 2001) and Campylobacter species(Ribot et al., 2001).

The reagents and reaction conditions listedin each of the protocols were determined by al-tering the parameters for each variable until asatisfactory result was obtained. It is worth not-ing that while the plug preparation steps arethe same for E. coli O157, Salmonella, andShigella, different organisms may require dif-ferent reagents or conditions than the ones de-scribed here in order to achieve a similar levelof pattern quality. In standardizing protocols,we evaluate each step to identify a set of con-ditions that would result in protocols that werehighly robust and reliable. Perhaps the mostdifficult step in the standardization process isthe testing and selection of the electrophoresisconditions to be used for the individual PFGEprotocol. Three issues must be considered

when attempting to identify the electrophore-sis parameters: (1) number of fragments gen-erated by the restriction enzyme being tested,(2) size range of those fragments, and (3) theuniformity and overall distribution of the re-striction fragments of the universal standard.Electrophoresis conditions that create largegaps between fragments of the standard strainmight affect the analysis of the images. Pulse-Net protocols require the use of a universalPFGE standard for the normalization of imagesduring the computer-assisted analysis usingBioNumerics software.

The rapid standardized PFGE protocol de-scribed above has been widely used by Pulse-Net participants to generate thousands of PFGEpatterns since 1998, underscoring its robust-ness and reproducibility. Timely PFGE analy-sis of isolates has enabled PulseNet laborato-ries to detect clusters of foodborne illness byhelping recognize outbreaks earlier than everbefore possible and has helped facilitate epi-demiologic investigations of many of theseclusters.

DISCLAIMER

Use of trade names is for identification onlyand does not imply endorsement by the Pub-lic Health Service or by the U.S. Department ofHealth and Human Services.

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Address reprint requests to:Dr. Efrain M. Ribot

Centers for Disease Control and Prevention1600 Clifton Rd., Mailstop C03

Atlanta, GA 30333

E-mail: [email protected]

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61. A. Januszkiewicz, J. Szych, W. Rastawicki, T. Wolkowicz, A. Chrost, B. Leszczynska, E. Kuzma, M. Roszkowska-Blaim,R. Gierczynski. 2011. Molecular epidemiology of shiga-toxin producing Escherichia coli household outbreak in Poland dueto secondary transmission of STEC O104:H4 from Germany. Journal of Medical Microbiology . [CrossRef]

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66. T. M. Gibreel, A. R. Dodgson, J. Cheesbrough, A. J. Fox, F. J. Bolton, M. Upton. 2011. Population structure, virulencepotential and antibiotic susceptibility of uropathogenic Escherichia coli from Northwest England. Journal of AntimicrobialChemotherapy . [CrossRef]

67. Y.-Y. Tien, H. Ushijima, M. Mizuguchi, S.-Y. Liang, C.-S. Chiou. 2011. Use of multilocus variable-number tandem repeatanalysis in molecular subtyping of Salmonella enterica serovar Typhi isolates. Journal of Medical Microbiology . [CrossRef]

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69. Tetsuya Harada , Junko Sakata , Masashi Kanki , Kazuko Seto , Masumi Taguchi , Yuko Kumeda . 2011. MolecularEpidemiological Investigation of a Diffuse Outbreak Caused by Salmonella enterica Serotype Montevideo Isolates in OsakaPrefecture, Japan. Foodborne Pathogens and Disease 8:10, 1083-1088. [Abstract] [Full Text HTML] [Full Text PDF] [FullText PDF with Links]

70. Jalusa D. Kich, Arlei Coldebella, Nelson Morés, Mariana Gomes Nogueira, Marisa Cardoso, Pina M. Fratamico, Jeffrey E.Call, Paula Fedorka-Cray, John B. Luchansky. 2011. Prevalence, distribution, and molecular characterization of Salmonellarecovered from swine finishing herds and a slaughter facility in Santa Catarina, Brazil. International Journal of FoodMicrobiology . [CrossRef]

71. A.-M. Salisbury, C. Bronowski, P. Wigley. 2011. Salmonella Virchow isolates from human and avian origins in England -molecular characterization and infection of epithelial cells and poultry. Journal of Applied Microbiology no-no. [CrossRef]

72. Angela H.A.M. van Hoek, Rob de Jonge, Wendy M. van Overbeek, El Bouw, Annemarie Pielaat, Joost H. Smid, BurkhardMalorny, Ernst Junker, Charlotta Löfström, Karl Pedersen, Henk J.M. Aarts, Lourens Heres. 2011. A quantitative approachtowards a better understanding of the dynamics of Salmonella spp. in a pork slaughter-line. International Journal of FoodMicrobiology . [CrossRef]

73. J. Campos, M. Pichel, T.M.I. Vaz, A.T. Tavechio, S.A. Fernandes, N. Muñoz, C. Rodriguez, M.E. Realpe, J. Moreno, P.Araya, J. Fernández, A. Fernández, E. Campos, F. Duarte, N. Weiler Gustafson, N. Binsztein, E. Pérez Gutierrez. 2011.Building PulseNet Latin America and Caribbean Salmonella regional database: First conclusions of genetic subtypes of S.Typhi, S. Typhimurium and S. Enteritidis circulating in six countries of the region. Food Research International . [CrossRef]

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75. Caterina Graziani , Luca Busani , Anna Maria Dionisi , Alfredo Caprioli , Sofie Ivarsson , Ingela Hedenström , Ida Luzzi .2011. Virulotyping of Salmonella enterica Serovar Napoli Strains Isolated in Italy from Human and Nonhuman Sources.Foodborne Pathogens and Disease 8:9, 997-1003. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

76. W. Zhang, Y. Luo, J. Li, L. Lin, Y. Ma, C. Hu, S. Jin, L. Ran, S. Cui. 2011. Wide dissemination of multidrug-resistant Shigellaisolates in China. Journal of Antimicrobial Chemotherapy . [CrossRef]

77. Elizabeth Cavallaro, Kashmira Date, Carlota Medus, Stephanie Meyer, Benjamin Miller, Clara Kim, Scott Nowicki, ShaunCosgrove, David Sweat, Quyen Phan, James Flint, Elizabeth R. Daly, Jennifer Adams, Eija Hyytia-Trees, Peter Gerner-Smidt,Robert M. Hoekstra, Colin Schwensohn, Adam Langer, Samir V. Sodha, Michael C. Rogers, Frederick J. Angulo, RobertV. Tauxe, Ian T. Williams, Casey Barton Behravesh. 2011. Salmonella Typhimurium Infections Associated with PeanutProducts. New England Journal of Medicine 365:7, 601-610. [CrossRef]

78. A. N. Sheth, M. Hoekstra, N. Patel, G. Ewald, C. Lord, C. Clarke, E. Villamil, K. Niksich, C. Bopp, T.-A. Nguyen, D. Zink,M. Lynch. 2011. A National Outbreak of Salmonella Serotype Tennessee Infections From Contaminated Peanut Butter: ANew Food Vehicle for Salmonellosis in the United States. Clinical Infectious Diseases 53:4, 356-362. [CrossRef]

79. E. Bielak, R. D. Bergenholtz, M. S. Jorgensen, S. J. Sorensen, L. H. Hansen, H. Hasman. 2011. Investigation of diversity ofplasmids carrying the blaTEM-52 gene. Journal of Antimicrobial Chemotherapy . [CrossRef]

80. S. Le Hello, R. S. Hendriksen, B. Doublet, I. Fisher, E. M. Nielsen, J. M. Whichard, B. Bouchrif, K. Fashae, S. A. Granier,N. Jourdan-Da Silva, A. Cloeckaert, E. J. Threlfall, F. J. Angulo, F. M. Aarestrup, J. Wain, F.-X. Weill. 2011. InternationalSpread of an Epidemic Population of Salmonella enterica Serotype Kentucky ST198 Resistant to Ciprofloxacin. Journal ofInfectious Diseases . [CrossRef]

81. A. BACKHANS, C. FELLSTRÖM, S. THISTED LAMBERTZ. 2011. Occurrence of pathogenic Yersinia enterocolitica andYersinia pseudotuberculosis in small wild rodents. Epidemiology and Infection 139:08, 1230-1238. [CrossRef]

82. K. H. KEDDY, A. SOOKA, H. ISMAIL, A. M. SMITH, I. WEBER, M. E. LETSOALO, B. N. HARRIS. 2011. Molecularepidemiological investigation of a typhoid fever outbreak in South Africa, 2005: the relationship to a previous epidemic in1993. Epidemiology and Infection 139:08, 1239-1245. [CrossRef]

83. Nina Christiansen , Lene Nielsen , Lotte Jakobsen , Marc Stegger , Lars Hestbjerg Hansen , Niels Frimodt-Møller . 2011.Fluoroquinolone Resistance Mechanisms in Urinary Tract Pathogenic Escherichia coli Isolated During Rapidly IncreasingFluoroquinolone Consumption in a Low-Use Country. Microbial Drug Resistance 17:3, 395-406. [Abstract] [Full TextHTML] [Full Text PDF] [Full Text PDF with Links]

84. Jiyong Yang , Yanping Luo , Shenghui Cui , Weiwei Wang , Li Han . 2011. Diverse Phenotypic and GenotypicCharacterization Among Clinical Klebsiella pneumoniae and Escherichia coli Isolates Carrying Plasmid-Mediated QuinoloneResistance Determinants. Microbial Drug Resistance 17:3, 363-367. [Abstract] [Full Text HTML] [Full Text PDF] [Full TextPDF with Links]

85. Vandan Nagar, Ravindranath Shashidhar, Jayant R. Bandekar. 2011. Prevalence, Characterization, and AntimicrobialResistance of Aeromonas Strains from Various Retail Food Products in Mumbai, India. Journal of Food Science no-no.[CrossRef]

86. Anna Maria Dionisi, Claudia Lucarelli, Ildo Benedetti, Slawomir Owczarek, Ida Luzzi. 2011. Molecular characterisation ofmultidrug-resistant Salmonella enterica serotype Infantis from humans, animals and the environment in Italy. InternationalJournal of Antimicrobial Agents . [CrossRef]

87. Elisabeth Hauser, Franka Hebner, Erhard Tietze, Reiner Helmuth, Ernst Junker, Rita Prager, Andreas Schroeter, WolfgangRabsch, Angelika Fruth, Burkhard Malorny. 2011. Diversity of Salmonella enterica serovar Derby isolated from pig, porkand humans in Germany. International Journal of Food Microbiology . [CrossRef]

88. S. Boisrame-Gastrin, D. Tande, M.-R. Munck, S. Gouriou, P. Nordmann, T. Naas. 2011. Salmonella carriage in adoptedchildren from Mali: 2001-08. Journal of Antimicrobial Chemotherapy . [CrossRef]

89. Annette Hartzell , Chun Chen , Carrie Lewis , Kuanqing Liu , Stanley Reynolds , Edward G. Dudley . 2011. Escherichia coliO157:H7 of Genotype Lineage-Specific Polymorphism Assay 211111 and Clade 8 Are Common Clinical Isolates WithinPennsylvania. Foodborne Pathogens and Disease 8:7, 763-768. [Abstract] [Full Text HTML] [Full Text PDF] [Full TextPDF with Links]

90. Charles C. Dodd , David G. Renter , Xiaorong Shi , M. Jahangir Alam , T.G. Nagaraja , Michael W. Sanderson . 2011.Prevalence and Persistence of Salmonella in Cohorts of Feedlot Cattle. Foodborne Pathogens and Disease 8:7, 781-789.[Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

91. M. P. SAUNDERS, G. WU, M. ABUOUN, Z. PAN, M. ANJUM, M. J. WOODWARD. 2011. Optical genetic mappingdefines regions of chromosomal variation in serovars of S. enterica subsp. enterica of concern for human and animal health.Epidemiology and Infection 139:07, 1065-1074. [CrossRef]

92. Bing-Mu Hsu, Kuan-Hao Huang, Shih-Wei Huang, Kuo-Chih Tseng, Ming-Jen Su, Wei-Chen Lin, Dar-Der Ji, Feng-ChengShih, Jyh-Larng Chen, Po-Min Kao. 2011. Evaluation of different analysis and identification methods for Salmonella detectionin surface drinking water sources. Science of The Total Environment . [CrossRef]

93. D. Wasyl, A. Hoszowski. 2011. First isolation of ESBL-producing Salmonella and emergence of multiresistant SalmonellaKentucky in turkey in Poland. Food Research International . [CrossRef]

94. Christina Frank, Dirk Werber, Jakob P. Cramer, Mona Askar, Mirko Faber, Matthias an der Heiden, Helen Bernard, AngelikaFruth, Rita Prager, Anke Spode, Maria Wadl, Alexander Zoufaly, Sabine Jordan, Markus J. Kemper, Per Follin, Luise Müller,Lisa A. King, Bettina Rosner, Udo Buchholz, Klaus Stark, Gérard Krause. 2011. Epidemic Profile of Shiga-Toxin–ProducingEscherichia coli O104:H4 Outbreak in Germany. New England Journal of Medicine 111026144204001. [CrossRef]

95. N. Bouzidi, L. Aoun, M. Dekhil, S. A. Granier, L. Poirel, A. Brisabois, P. Nordmann, Y. Millemann. 2011. Co-occurrenceof aminoglycoside resistance gene armA in non-Typhi Salmonella isolates producing CTX-M-15 in Algeria. Journal ofAntimicrobial Chemotherapy . [CrossRef]

96. S. Ghosh, G. P. Pazhani, G. Chowdhury, S. Guin, S. Dutta, K. Rajendran, M. K. Bhattacharya, Y. Takeda, S. K. Niyogi, G.B. Nair, T. Ramamurthy. 2011. Genetic Characteristics and Changing Antimicrobial Resistance among Shigella spp Isolatedfrom Hospitalized Diarrhoeal Patients in Kolkata, India. Journal of Medical Microbiology . [CrossRef]

97. Rebecca L. Lindsey , Jonathan G. Frye , Sutawee N. Thitaram , Richard J. Meinersmann , Paula J. Fedorka-Cray , MarkD. Englen . 2011. Characterization of Multidrug-Resistant Escherichia coli by Antimicrobial Resistance Profiles, PlasmidReplicon Typing, and Pulsed-Field Gel Electrophoresis. Microbial Drug Resistance 17:2, 157-163. [Abstract] [Full TextHTML] [Full Text PDF] [Full Text PDF with Links]

98. Abraham J. Niehaus , Teke Apalata , Yacoob M. Coovadia , Anthony M. Smith , Prashini Moodley . 2011. An Outbreak ofFoodborne Salmonellosis in Rural KwaZulu-Natal, South Africa. Foodborne Pathogens and Disease 8:6, 693-697. [Abstract][Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

99. Randi Føns Petersen , Eva Litrup , Jonas T. Larsson , Mia Torpdahl , Gitte Sørensen , Luise Müller , Eva M. Nielsen .2011. Molecular Characterization of Salmonella Typhimurium Highly Successful Outbreak Strains. Foodborne Pathogensand Disease 8:6, 655-661. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

100. J. B. Nielsen, M. N. Skov, R. L. Jørgensen, O. Heltberg, D. S. Hansen, K. Schønning. 2011. Identification of CTX-M15-,SHV-28-producing Klebsiella pneumoniae ST15 as an epidemic clone in the Copenhagen area using a semi-automated Rep-PCR typing assay. European Journal of Clinical Microbiology & Infectious Diseases 30:6, 773-778. [CrossRef]

101. Louise Bélanger, Amélie Garenaux, Josée Harel, Martine Boulianne, Eric Nadeau, Charles M. Dozois. 2011. Escherichia coli from animal reservoirs as a potential source of human extraintestinal pathogenic E. coli. FEMS Immunology & MedicalMicrobiology 62:1, 1-10. [CrossRef]

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103. Kwai Lin Thong, Wai Ling Lai, Amreeta Dhanoa. 2011. Antimicrobial susceptibility and pulsed – Field Gel Electrophoreticanalysis of Salmonella in a tertiary hospital in northern Malaysia. Journal of Infection and Public Health 4:2, 65-72.[CrossRef]

104. N.H. Martin, S.C. Murphy, R.D. Ralyea, M. Wiedmann, K.J. Boor. 2011. When cheese gets the blues: Pseudomonasfluorescens as the causative agent of cheese spoilage. Journal of Dairy Science 94:6, 3176-3183. [CrossRef]

105. B. Verbist, V. Piessens, A. Van Nuffel, L. De Vuyst, M. Heyndrickx, L. Herman, E. Van Coillie, S. De Vliegher. 2011.Sources other than unused sawdust can introduce Klebsiella pneumoniae into dairy herds. Journal of Dairy Science 94:6,2832-2839. [CrossRef]

106. K. Hoelzer, K.J. Cummings, E.M. Wright, L.D. Rodriguez-Rivera, S.E. Roof, A.I. Moreno Switt, N. Dumas, T. Root, D.J.Schoonmaker-Bopp, Y.T. Grohn, J.D. Siler, L.D. Warnick, D.D. Hancock, M.A. Davis, M. Wiedmann. 2011. SalmonellaCerro isolated over the past twenty years from various sources in the US represent a single predominant pulsed-field gelelectrophoresis type. Veterinary Microbiology 150:3-4, 389-393. [CrossRef]

107. Felicita Medalla, Maria Sjölund-Karlsson, Sanghyuk Shin, Emily Harvey, Kevin Joyce, Lisa Theobald, Benjamin L. Nygren,Gary Pecic, Kathryn Gay, Jana Austin, Andrew Stuart, Elizabeth Blanton, Eric D. Mintz, Jean M. Whichard, Ezra J. Barzilay.2011. Ciprofloxacin-Resistant Salmonella enterica Serotype Typhi, United States, 1999–2008. Emerging Infectious Diseases17:6, 1095-1098. [CrossRef]

108. J. K. SCHAFFZIN, F. CORONADO, N. B. DUMAS, T. P. ROOT, T. A. HALSE, D. J. SCHOONMAKER-BOPP, M. M.LURIE, D. NICHOLAS, B. GERZONICH, G. S. JOHNSON, B. J. WALLACE, K. A. MUSSER. 2011. Public health approachto detection of non-O157 Shiga toxin-producing Escherichia coli: summary of two outbreaks and laboratory procedures.Epidemiology and Infection 1-7. [CrossRef]

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110. Irene V. Wesley, Wayne T. Muraoka. 2011. Time of Entry of Salmonella and Campylobacter into the Turkey Brooder House.Food and Bioprocess Technology 4:4, 616-623. [CrossRef]

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114. A. M. Smith, K. H. Keddy, H. Ismail, J. Thomas, R. van der Gryp, M. J. Manamela, M. Huma, A. Sooka, L. K. Theobald,M. A. Mennen, L. C. O'Reilly. 2011. International collaboration tracks typhoid fever cases over two continents from SouthAfrica to Australia. Journal of Medical Microbiology . [CrossRef]

115. A. M. EL-GENDY, A. MANSOUR, M. A. WEINER, G. PIMENTEL, A. W. ARMSTRONG, S. Y. N. YOUNG, N.ELSAYED, J. D. KLENA. 2011. Genetic diversity and antibiotic resistance in Shigella dysenteriae and Shigella boydii strainsisolated from children aged <5 years in Egypt. Epidemiology and Infection 1-12. [CrossRef]

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117. A. M. Hammerum, C. H. Lester, L. Jakobsen, L. J. Porsbo. 2011. Faecal carriage of extended-spectrum #-lactamase-producingand AmpC #-lactamase-producing bacteria among Danish army recruits. Clinical Microbiology and Infection 17:4, 566-568.[CrossRef]

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119. S. A. Lowther, C. Medus, J. Scheftel, F. Leano, S. Jawahir, K. Smith. 2011. Foodborne Outbreak of Salmonella SubspeciesIV Infections Associated with Contamination from Bearded Dragons. Zoonoses and Public Health no-no. [CrossRef]

120. Eleni Galanis, Jane Parmley, Nancy De With. 2011. Integrated surveillance of Salmonella along the food chain using existingdata and resources in British Columbia, Canada. Food Research International . [CrossRef]

121. Roberto Marrero-Ortiz, Jing Han, Aaron M. Lynne, Donna E. David, Mary E. Stemper, Doris Farmer, William Burkhardt,Rajesh Nayak, Steven L. Foley. 2011. Genetic characterization of antimicrobial resistance in Salmonella enterica serovarsisolated from dairy cattle in Wisconsin. Food Research International . [CrossRef]

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123. Ginger M. Shipp , James S. Dickson . 2011. The Establishment of Enterobacteriaceae and Salmonella London in a New DairyFarm Environment. Foodborne Pathogens and Disease 8:3, 411-420. [Abstract] [Full Text HTML] [Full Text PDF] [FullText PDF with Links]

124. Koo-Youn Kim, Jong-Hyun Park, Hyo-Sun Kwak, Gun-Jo Woo. 2011. Characterization of the quinolone resistancemechanism in foodborne Salmonella isolates with high nalidixic acid resistance. International Journal of Food Microbiology146:1, 52-56. [CrossRef]

125. K. H. DYET, I. ROBERTSON, E. TURBITT, P. E. CARTER. 2011. Characterization of Escherichia coli O157:H7 inNew Zealand using multiple-locus variable-number tandem-repeat analysis. Epidemiology and Infection 139:03, 464-471.[CrossRef]

126. M. Aurora Echeita Sarrionandia, Silvia Herrera León, Cristina Simón Baamonde. 2011. Gastroenteritis invasivas, ¿algonuevo?. Enfermedades Infecciosas y Microbiología Clínica 29, 55-60. [CrossRef]

127. Srirat Pornruangwong , Rene S. Hendriksen , Chaiwat Pulsrikarn , Aroon Bangstrakulnonth , Matthew Mikoleit , Rob H.Davies , Frank M. Aarestrup , Lourdes Garcia-Migura . 2011. Epidemiological Investigation of Salmonella enterica SerovarKedougou in Thailand. Foodborne Pathogens and Disease 8:2, 203-211. [Abstract] [Full Text HTML] [Full Text PDF] [FullText PDF with Links]

128. S. V. SODHA, M. LYNCH, K. WANNEMUEHLER, M. LEEPER, M. MALAVET, J. SCHAFFZIN, T. CHEN, A. LANGER,M. GLENSHAW, D. HOEFER, N. DUMAS, L. LIND, M. IWAMOTO, T. AYERS, T. NGUYEN, M. BIGGERSTAFF,C. OLSON, A. SHETH, C. BRADEN. 2011. Multistate outbreak of Escherichia coli O157:H7 infections associated with anational fast-food chain, 2006: a study incorporating epidemiological and food source traceback results. Epidemiology andInfection 139:02, 309-316. [CrossRef]

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130. Celine Mannion, June Fanning, Joanne McLernon, Lynsey Lendrum, Montserrat Gutierrez, Sharon Duggan, John Egan. 2011.The role of transport, lairage and slaughter processes in the dissemination of Salmonella spp. in pigs in Ireland. Food ResearchInternational . [CrossRef]

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132. Ryan M Stepan, Julie S Sherwood, Shana R Petermann, Catherine M Logue. 2011. Molecular and Comparative Analysisof Salmonella enterica Senftenberg from Humans and Animals using PFGE, MLST and NARMS. BMC Microbiology 11:1,153. [CrossRef]

133. Leila M Sihvonen, Susanna Toivonen, Kaisa Haukka, Markku Kuusi, Mikael Skurnik, Anja Siitonen. 2011. MultilocusVariable-Number Tandem-Repeat Analysis, Pulsed-Field Gel Electrophoresis, and Antimicrobial Susceptibility Patterns inDiscrimination of Sporadic and Outbreak-Related Strains of Yersinia enterocolitica. BMC Microbiology 11:1, 42. [CrossRef]

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135. Hesham Dahshan, Mahdy A. Abd-El-Kader, Takehisa Chuma, Hiraku Moriki, Karoku Okamoto. 2011. Re-emergence ofmulti-drug resistant Salmonella enterica serovar Stanley from cattle. Veterinary Research Communications 35:1, 55-60.[CrossRef]

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137. Yung-Yen Tien, You-Wun Wang, Sheng Kai Tung, Shiu-Yun Liang, Chien-Shun Chiou. 2011. Comparison of multilocusvariable-number tandem repeat analysis and pulsed-field gel electrophoresis in molecular subtyping of Salmonella entericaserovars Paratyphi A. Diagnostic Microbiology and Infectious Disease 69:1, 1-6. [CrossRef]

138. Henk C den Bakker, Andrea I Moreno Switt, Gregory Govoni, Craig A Cummings, Matthew L Ranieri, Lovorka Degoricija,Karin Hoelzer, Lorraine D Rodriguez-Rivera, Stephanie Brown, Elena Bolchacova, Manohar R Furtado, Martin Wiedmann.2011. Genome sequencing reveals diversification of virulence factor content and possible host adaptation in distinctsubpopulations of Salmonella enterica. BMC Genomics 12:1, 425. [CrossRef]

139. Jean Guard, Cesar A Morales, Paula Fedorka-Cray, Richard K Gast. 2011. Single Nucleotide Polymorphisms that DifferentiateTwo Subpopulations of Salmonella Enteritidis Within Phage Type. BMC Research Notes 4:1, 369. [CrossRef]

140. Baowei Yang, Meili Xi, Shenghui Cui, Xiuli Zhang, Jinling Shen, Min Sheng, Dong Qu, Xin Wang, Jianghong Meng. 2011.Mutations in gyrase and topoisomerase genes associated with fluoroquinolone resistance in Salmonella serovars from retailmeats. Food Research International . [CrossRef]

141. Ming-Hui Chen, Chien-Shun Chiou, Yu-Cheng Chiang, Pin-Hsin Chen, Shuo-Wen Tsai, Hau-Yang Tsen. 2011. Comparisonof the pulsed field gel electrophoresis patterns and virulence profiles of the multidrug resistant strains of Salmonella entericaserovar Schwarzengrund isolated from chicken meat and humans in Taiwan. Food Research International . [CrossRef]

142. K. L. F. CooperPulsed-field gel electrophoresis and other commonly used molecular methods for subtyping of foodbornebacteria 157-180. [CrossRef]

143. E. K. Hyytia-TreesDevelopment, validation and quality assurance of methods for subtyping of foodborne pathogens 214-234.[CrossRef]

144. Maria Sjölund-Karlsson , Regan Rickert , Caline Matar , Gary Pecic , Rebecca L. Howie , Kevin Joyce , Felicita Medalla ,Ezra J. Barzilay , Jean M. Whichard . 2010. Salmonella Isolates with Decreased Susceptibility to Extended-SpectrumCephalosporins in the United States. Foodborne Pathogens and Disease 7:12, 1503-1509. [Abstract] [Full Text HTML] [FullText PDF] [Full Text PDF with Links]

145. Thomas E. Wittum , Dixie F. Mollenkopf , Joshua B. Daniels , Anne E. Parkinson , Jennifer L. Mathews , Pamela R. Fry ,Melanie J. Abley , Wondwossen A. Gebreyes . 2010. CTX-M-Type Extended-Spectrum #-Lactamases Present in Escherichiacoli from the Feces of Cattle in Ohio, United States. Foodborne Pathogens and Disease 7:12, 1575-1579. [Abstract] [FullText HTML] [Full Text PDF] [Full Text PDF with Links]

146. S.N. Melendez, I. Hanning, J. Han, R. Nayak, A.R. Clement, A. Wooming, P. Hererra, F.T. Jones, S.L. Foley, S.C. Ricke.2010. Salmonella enterica isolates from pasture-raised poultry exhibit antimicrobial resistance and class I integrons. Journalof Applied Microbiology 109:6, 1957-1966. [CrossRef]

147. M. Karama, C. L. Gyles. 2010. Methods for Genotyping Verotoxin-Producing Escherichia coli. Zoonoses and Public Health57:7-8, 447-462. [CrossRef]

148. Mohammad A. Islam , Abdus S. Mondol , Ishrat J. Azmi , Enne de Boer , Rijkelt R. Beumer , Marcel H. Zwietering , Annet E.Heuvelink , Kaisar A. Talukder . 2010. Occurrence and Characterization of Shiga Toxin–Producing Escherichia coli in Raw

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149. Walid Q. Alali , Siddhartha Thakur , Roy D. Berghaus , Michael P. Martin , Wondwossen A. Gebreyes . 2010. Prevalenceand Distribution of Salmonella in Organic and Conventional Broiler Poultry Farms. Foodborne Pathogens and Disease 7:11,1363-1371. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

150. Florian Mertes, Katja Biens, Hans Lehrach, Martin Wagner, Andreas Dahl. 2010. High-throughput Universal ProbeSalmonella Serotyping (UPSS) by nanoPCR. Journal of Microbiological Methods 83:2, 217-223. [CrossRef]

151. Joshua M. Rounds, Craig W. Hedberg, Stephanie Meyer, David J. Boxrud, Kirk E. Smith. 2010. Salmonella entericaPulsed-Field Gel Electrophoresis Clusters, Minnesota, USA, 2001–2007. Emerging Infectious Diseases 16:11, 1678-1685.[CrossRef]

152. Cindy Dierikx, Alieda van Essen-Zandbergen, Kees Veldman, Hilde Smith, Dik Mevius. 2010. Increased detection ofextended spectrum beta-lactamase producing Salmonella enterica and Escherichia coli isolates from poultry. VeterinaryMicrobiology 145:3-4, 273-278. [CrossRef]

153. Maria Ström-Bestor, Noora Mustamäki, Sirpa Heinikainen, Varpu Hirvelä-Koski, David Verner-Jeffreys, Tom Wiklund.2010. Introduction of Yersinia ruckeri biotype 2 into Finnish fish farms. Aquaculture 308:1-2, 1-5. [CrossRef]

154. John B. Kaneene , RoseAnn Miller , Katherine May , Joseph A. Hattey . 2010. An Outbreak of Multidrug-Resistant Salmonellaenterica Serotype Oranienburg in Michigan Dairy Calves. Foodborne Pathogens and Disease 7:10, 1193-1201. [Abstract][Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

155. Richard V. Goering. 2010. Pulsed field gel electrophoresis: A review of application and interpretation in the molecularepidemiology of infectious disease. Infection, Genetics and Evolution 10:7, 866-875. [CrossRef]

156. Soumik Barman, Sohini Chatterjee, Goutam Chowdhury, Thandavarayan Ramamurthy, Swapan Kumar Niyogi, RanajitKumar, Hemanta Koley. 2010. Plasmid-mediated streptomycin and sulfamethoxazole resistance in Shigella flexneri 3a.International Journal of Antimicrobial Agents 36:4, 348-351. [CrossRef]

157. Hesham Dahshan, Francis Shahada, Takehisa Chuma, Hiraku Moriki, Karoku Okamoto. 2010. Genetic analysis of multidrug-resistant Salmonella enterica serovars Stanley and Typhimurium from cattle. Veterinary Microbiology 145:1-2, 76-83.[CrossRef]

158. Elizabeth R. Daly , Colleen M. Smith , Peter Wikoff , John Seiferth , Jayne Finnigan , Alisha M. Nadeau , Joyce J. Welch .2010. Salmonella Enteritidis Infections Associated with a Contaminated Immersion Blender at a Camp. Foodborne Pathogensand Disease 7:9, 1083-1088. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

159. Prapas Patchanee , Bayleyegn Molla , Nancy White , Daniel E. Line , Wondwossen A. Gebreyes . 2010. Tracking SalmonellaContamination in Various Watersheds and Phenotypic and Genotypic Diversity. Foodborne Pathogens and Disease 7:9,1113-1120. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

160. Yadira Lugo-Melchor , Beatriz Quiñones , Bianca A. Amézquita-López , Josefina León-Félix , Raymundo García-Estrada ,Cristóbal Chaidez . 2010. Characterization of Tetracycline Resistance in Salmonella enterica Strains Recovered fromIrrigation Water in the Culiacan Valley, Mexico. Microbial Drug Resistance 16:3, 185-190. [Abstract] [Full Text HTML][Full Text PDF] [Full Text PDF with Links]

161. Liana J. Borges, Maria Raquel H. Campos, Juliana L. Cardoso, Maria Cláudia D.P.B. André, Álvaro B. Serafini. 2010.Molecular Epidemiology of Microorganisms Isolated from Food Workers and Enteral Feeding of Public Hospitals. Journalof Food Science 75:7, M449-M454. [CrossRef]

162. M. Pablos, M.-A. Remacha, J.-M. Rodríguez-Calleja, J. A. Santos, A. Otero, M.-L. García-López. 2010. Identity, virulencegenes, and clonal relatedness of Aeromonas isolates from patients with diarrhea and drinking water. European Journal ofClinical Microbiology & Infectious Diseases 29:9, 1163-1172. [CrossRef]

163. Lisa A. King, Ingrid Filliol-Toutain, Patricia Mariani-Kurkidjian, Véronique Vaillant, Christine Vernozy-Rozand, SarahGanet, Nathalie Pihier, Patrick Niaudet, Henriette de Valk. 2010. Family Outbreak of Shiga Toxin–producing Escherichiacoli O123:H–, France, 2009. Emerging Infectious Diseases 16:9, 1491-1493. [CrossRef]

164. Aliya Naheed, Pavani K. Ram, W. Abdullah Brooks, M. Anowar Hossain, Michele B. Parsons, Kaisar Ali Talukder, EricMintz, Stephen Luby, Robert F. Breiman. 2010. Burden of typhoid and paratyphoid fever in a densely populated urbancommunity, Dhaka, Bangladesh. International Journal of Infectious Diseases 14, e93-e99. [CrossRef]

165. Erin Hedican , Ben Miller , Brian Ziemer , Pam LeMaster , Selina Jawahir , Fe Leano , Kirk Smith . 2010. SalmonellosisOutbreak Due to Chicken Contact Leading to a Foodborne Outbreak Associated with Infected Delicatessen Workers.Foodborne Pathogens and Disease 7:8, 995-997. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

166. Peter C.H. Feng, Christine Keys, David Lacher, Steven R. Monday, Dan Shelton, Christine Rozand, Marta Rivas, ThomasWhittam. 2010. Prevalence, characterization and clonal analysis of Escherichia coli O157: non-H7 serotypes that carry eaealleles. FEMS Microbiology Letters 308:1, 62-67. [CrossRef]

167. Ekaterina Protozanova, Meng Zhang, Eric J. White, Emilia T. Mollova, Dirk Ten Broeck, Sergey V. Fridrikh, Douglas B.Cameron, Rudolf Gilmanshin. 2010. Fast high-resolution mapping of long fragments of genomic DNA based on single-molecule detection. Analytical Biochemistry 402:1, 83-90. [CrossRef]

168. Kevin J. Cummings , Thomas J. Divers , Patrick L. McDonough , Andrea Moreno Switt , Martin Wiedmann , Lorin D.Warnick . 2010. Temporal Clusters of Bovine Salmonella Cases at a Veterinary Medical Teaching Hospital, 1996–2007.Vector-Borne and Zoonotic Diseases 10:5, 471-479. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

169. Ye#im Soyer , Samuel D. Alcaine , Dainna J. Schoonmaker-Bopp , Timothy P. Root , Lorin D. Warnick , Patrick L.McDonough , Nellie B. Dumas , Yrjo T. Gröhn , Martin Wiedmann . 2010. Pulsed-Field Gel Electrophoresis Diversity ofHuman and Bovine Clinical Salmonella Isolates. Foodborne Pathogens and Disease 7:6, 707-717. [Abstract] [Full TextHTML] [Full Text PDF] [Full Text PDF with Links] [Supplemental material]

170. Kevin J. Cummings , Lorin D. Warnick , Mara Elton , Lorraine D. Rodriguez-Rivera , Julie D. Siler , Emily M. Wright , YrjoT. Gröhn , Martin Wiedmann . 2010. Salmonella enterica Serotype Cerro Among Dairy Cattle in New York: An EmergingPathogen?. Foodborne Pathogens and Disease 7:6, 659-665. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDFwith Links]

171. Chien-Shun Chiou, Hsin-Yi Li, Sheng-Kai Tung, Chien-Yen Chen, Ching-Hao Teng, Jwu-Ching Shu, Joseph T. Tseng, Chi-Yu Hsu, Chien-Cheng Chen. 2010. Identification of prophage gene z2389 in Escherichia coli EDL933 encoding a DNAcytosine methyltransferase for full protection of NotI sites. International Journal of Medical Microbiology 300:5, 296-303.[CrossRef]

172. J. STELLING, W. K. YIH, M. GALAS, M. KULLDORFF, M. PICHEL, R. TERRAGNO, E. TUDURI, S. ESPETXE, N.BINSZTEIN, T. F. O'BRIEN, R. PLATT. 2010. Automated use of WHONET and SaTScan to detect outbreaks of Shigellaspp. using antimicrobial resistance phenotypes. Epidemiology and Infection 138:06, 873. [CrossRef]

173. Noémi Nógrády , Ariel Imre , Ágnes Kostyák , Ákos Tóth , Béla Nagy . 2010. Molecular and Pathogenic Characterizationof Salmonella enterica Serovar Bovismorbificans Strains of Animal, Environmental, Food, and Human Origin in Hungary.Foodborne Pathogens and Disease 7:5, 507-513. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

174. D. Tande, S. Boisrame-Gastrin, M. R. Munck, G. Hery-Arnaud, S. Gouriou, N. Jallot, P. Nordmann, T. Naas. 2010.Intrafamilial transmission of extended-spectrum- -lactamase-producing Escherichia coli and Salmonella enterica Babelsbergamong the families of internationally adopted children. Journal of Antimicrobial Chemotherapy 65:5, 859-865. [CrossRef]

175. T. R. Thorsteinsdottir, G. Haraldsson, V. Fridriksdottir, K. G. Kristinsson, E. Gunnarsson. 2010. Prevalence and GeneticRelatedness of Antimicrobial-Resistant Escherichia coli Isolated From Animals, Foods and Humans in Iceland. Zoonoses andPublic Health 57:3, 189-196. [CrossRef]

176. Karen H. Keddy, Anthony M. Smith, Arvinda Sooka, Husna Ismail, Stephen Oliver. 2010. Fluoroquinolone-ResistantTyphoid, South Africa. Emerging Infectious Diseases 16:5, 879-880. [CrossRef]

177. Cristina Lanzas , Lorin D. Warnick , Karen L. James , Emily M. Wright , Martin Wiedmann , Yrjo T. Gröhn . 2010.Transmission Dynamics of a Multidrug-Resistant Salmonella Typhimurium Outbreak in a Dairy Farm. Foodborne Pathogensand Disease 7:4, 467-474. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

178. Charles C. Dodd , David G. Renter , J. Trent Fox , Xiaorong Shi , Michael W. Sanderson , T.G. Nagaraja . 2010. GeneticRelatedness of Escherichia coli O157 Isolates from Cattle Feces and Preintervention Beef Carcasses. Foodborne Pathogensand Disease 7:4, 357-365. [Abstract] [Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

179. J. Lindsay Oaks, Thomas E. Besser, Seth T. Walk, David M. Gordon, Kimberlee B. Beckmen, Kathy A. Burek, Gary J.Haldorson, Dan S. Bradway, Lindsey Ouellette, Fred R. Rurangirwa, Margaret A. Davis, Greg Dobbin, Thomas S. Whittam.2010. Escherichia albertii in Wild and Domestic Birds. Emerging Infectious Diseases 16:4, 638-646. [CrossRef]

180. Jessica L. Halpin , Nancy M. Garrett , Efrain M. Ribot , Lewis M. Graves , Kara L. Cooper . 2010. Re-evaluation,Optimization, and Multilaboratory Validation of the PulseNet-Standardized Pulsed-Field Gel Electrophoresis Protocol forListeria monocytogenes. Foodborne Pathogens and Disease 7:3, 293-298. [Abstract] [Full Text HTML] [Full Text PDF][Full Text PDF with Links]

181. J. Yang, Y. Luo, J. Li, Y. Ma, C. Hu, S. Jin, L. Ye, S. Cui. 2010. Characterization of clinical Escherichia coli isolates fromChina containing transferable quinolone resistance determinants. Journal of Antimicrobial Chemotherapy 65:3, 453-459.[CrossRef]

182. Jason P. Folster , Gary Pecic , Shanna Bolcen , Lisa Theobald , Kelley Hise , Alessandra Carattoli , Shaohua Zhao , Patrick F.McDermott , Jean M. Whichard . 2010. Characterization of Extended-Spectrum Cephalosporin–Resistant Salmonella entericaSerovar Heidelberg Isolated from Humans in the United States. Foodborne Pathogens and Disease 7:2, 181-187. [Abstract][Full Text HTML] [Full Text PDF] [Full Text PDF with Links]

183. Brandon Kinley, James Rieck, Paul Dawson, Xiuping Jiang. 2010. Analysis of Salmonella and enterococci isolated fromrendered animal products. Canadian Journal of Microbiology 56:1, 65-73. [CrossRef]

184. Hesham DAHSHAN, Takehisa CHUMA, Francis SHAHADA, Masato AKIBA, Hideki FUJIMOTO, Keishirou AKASAKA,Yuji KAMIMURA, Karoku OKAMOTO. 2010. Characterization of Antibiotic Resistance and the Emergence of AmpC-Producing Salmonella Infantis from Pigs. Journal of Veterinary Medical Science 72:11, 1437-1442. [CrossRef]

185. Clifford G. Clark, Christopher C. R. Grant, Keri M. Trout-Yakel, Helen Tabor, Lai-King Ng, Kris Rahn, Kristyn Franklin,Andrew M. Kropinski. 2010. The O28 Antigen Gene Clusters of Salmonella enterica subsp. enterica Serovar Dakar andSerovar Pomona Are Different. International Journal of Microbiology 2010, 1-8. [CrossRef]

186. Thorunn R. Thorsteinsdottir, Gunnsteinn Haraldsson, Vala Fridriksdottir, Karl G. Kristinsson, Eggert Gunnarsson. 2010.Broiler Chickens as Source of Human Fluoroquinolone-Resistant Escherichia coli , Iceland. Emerging Infectious Diseases16:1, 133-135. [CrossRef]

187. R. Terragno, A. Salve, M. Pichel, S. Epszteyn, S. Brengi, N. Binsztein. 2009. Characterization and subtyping of Cronobacterspp. from imported powdered infant formulae in Argentina. International Journal of Food Microbiology 136:2, 193-197.[CrossRef]

188. Toni L. Poole , Tom S. Edrington , Dayna M. Brichta-Harhay , Alessandra Carattoli , Robin Carl Anderson , David J. Nisbet .2009. Conjugative Transferability of the A/C Plasmids from Salmonella enterica Isolates That Possess or Lack blaCMY inthe A/C Plasmid Backbone. Foodborne Pathogens and Disease 6:10, 1185-1194. [Abstract] [Full Text PDF] [Full Text PDFwith Links]

189. Mark J. Sotir, Gwen Ewald, Akiko C. Kimura, Jeffrey I. Higa, Anandi Sheth, Scott Troppy, Stephanie Meyer, R MichaelHoekstra, Jana Austin, John Archer, Mary Spayne, Elizabeth R. Daly, Patricia M. Griffin. 2009. Outbreak of SalmonellaWandsworth and Typhimurium Infections in Infants and Toddlers Traced to a Commercial Vegetable-Coated Snack Food.The Pediatric Infectious Disease Journal 28:12, 1041-1046. [CrossRef]

190. Andreja Rajkovic, Nada Smigic, Mieke Uyttendaele, Helga Medic, Lieven de Zutter, Frank Devlieghere. 2009. Resistanceof Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni after exposure to repetitive cycles of mildbactericidal treatments. Food Microbiology 26:8, 889-895. [CrossRef]

191. H. Izumiya, Y. Tada, K. Ito, T. Morita-Ishihara, M. Ohnishi, J. Terajima, H. Watanabe. 2009. Characterization of Shigellasonnei isolates from travel-associated cases in Japan. Journal of Medical Microbiology 58:11, 1486-1491. [CrossRef]

192. A. Endimiani, J. M. DePasquale, S. Forero, F. Perez, A. M. Hujer, D. Roberts-Pollack, P. D. Fiorella, N. Pickens, B. Kitchel,A. E. Casiano-Colon, F. C. Tenover, R. A. Bonomo. 2009. Emergence of blaKPC-containing Klebsiella pneumoniae in a long-term acute care hospital: a new challenge to our healthcare system. Journal of Antimicrobial Chemotherapy 64:5, 1102-1110.[CrossRef]

193. German B. Vigo , Javier A. Cappuccio , Pablo E. Piñeyro , Angela Salve , Mariana A. Machuca , Maria A. Quiroga , FabianaMoredo , Gabriel Giacoboni , Jose L. Cancer , Ines G. Caffer , Norma Binsztein , Mariana Pichel , Carlos J. Perfumo . 2009.Salmonella enterica Subclinical Infection: Bacteriological, Serological, Pulsed-Field Gel Electrophoresis, and AntimicrobialResistance Profiles—Longitudinal Study in a Three-Site Farrow-to-Finish Farm. Foodborne Pathogens and Disease 6:8,965-972. [Abstract] [Full Text PDF] [Full Text PDF with Links]

194. Luc Belloy, Loane Decrausaz, Patrick Boujon, Herbert Hächler, Andreas S. Waldvogel. 2009. Diagnosis by culture and PCRof Salmonella Abortusovis infection under clinical conditions in aborting sheep in Switzerland. Veterinary Microbiology138:3-4, 373-377. [CrossRef]

195. Insook Son , Jo Ann S. Van Kessel , Jeffrey S. Karns . 2009. Genotypic Diversity of Escherichia coli in a Dairy Farm.Foodborne Pathogens and Disease 6:7, 837-847. [Abstract] [Full Text PDF] [Full Text PDF with Links]

196. Kek Heng Chua, Kah Heng See, S.D. Puthucheary. 2009. Use of Plastic Primer Container Covers as Effective Plug Moldsfor Pulsed-Field Gel Electrophoresis. Journal of Applied Sciences 9:9, 1798-1800. [CrossRef]

197. Rene S. Hendriksen, Matthew Mikoleit, Christian Kornschober, Regan L. Rickert, Susan Van Duyne, Charlotte Kjelsø,Henrik Hasman, Martin Cormican, Dik Mevius, John Threlfall, Frederic J. Angulo, Frank M. Aarestrup. 2009. Emergenceof Multidrug-Resistant Salmonella Concord Infections in Europe and the United States in Children Adopted From Ethiopia,2003–2007. The Pediatric Infectious Disease Journal 28:9, 814-818. [CrossRef]

198. Aaron M. Lynne, Lindsay L. Dorsey, Donna E. David, Steven L. Foley. 2009. Characterisation of antibiotic resistance inhost-adapted Salmonella enterica. International Journal of Antimicrobial Agents 34:2, 169-172. [CrossRef]

199. Emilia T. Mollova, Vishal A. Patil, Ekaterina Protozanova, Meng Zhang, Rudolf Gilmanshin. 2009. An automated samplepreparation system with mini-reactor to isolate and process submegabase fragments of bacterial DNA. Analytical Biochemistry391:2, 135-143. [CrossRef]

200. Anna Maria Dionisi , Caterina Graziani , Claudia Lucarelli , Emma Filetici , Laura Villa , Slawomir Owczarek , AlfredoCaprioli , Ida Luzzi . 2009. Molecular Characterization of Multidrug-Resistant Strains of Salmonella enterica SerotypeTyphimurium and Monophasic Variant (S. 4,[5],12:i:–) Isolated from Human Infections in Italy. Foodborne Pathogens andDisease 6:6, 711-717. [Abstract] [Full Text PDF] [Full Text PDF with Links]

201. Shukho Kim , Sung-Hun Kim , Jeong-Hyun Park , Kyung-Shin Lee , Mi-Sun Park , Bok Kwon Lee . 2009. Clustering Analysisof Salmonella enterica Serovar Typhi Isolates in Korea by PFGE, Ribotyping, and Phage Typing. Foodborne Pathogens andDisease 6:6, 733-738. [Abstract] [Full Text PDF] [Full Text PDF with Links]

202. C. G. Clark, A. M. Kropinski, H. Parolis, C. C. R. Grant, K. M. Trout-Yakel, K. Franklin, L.-K. Ng, N. A. Paramonov, L. A.S. Parolis, K. Rahn, H. Tabor. 2009. Escherichia coli O123 O antigen genes and polysaccharide structure are conserved insome Salmonella enterica serogroups. Journal of Medical Microbiology 58:7, 884-894. [CrossRef]

203. Ian S.T. Fisher , Nathalie Jourdan-Da Silva , Herbert Hächler , François-Xavier Weill , Hans Schmid , Corinne Danan ,Annaelle Kérouanton , Christopher R. Lane , Annamaria M. Dionisi , Ida Luzzi . 2009. Human Infections Due to SalmonellaNapoli: A Multicountry, Emerging Enigma Recognized by the Enter-net International Surveillance Network. FoodbornePathogens and Disease 6:5, 613-619. [Abstract] [Full Text PDF] [Full Text PDF with Links]

204. Lilia Lopez-Canovas, Ana Maria Riveron, Yainelis Garrido, Fidel Corrales, Adalberto Aguila, Yamilet Cárdenas. 2009.Adapting to contour-clamped homogeneous electric field minichamber technology the PulseNet protocols to resolve XbaI–DNA fragments of Salmonella serotype Braenderup. Analytical Biochemistry 388:2, 339-341. [CrossRef]

205. Stephan Huehn , Reiner Helmuth , Cornelia Bunge , Beatriz Guerra , Ernst Junker , Rob H. Davies , Pierre Wattiau , Wilfridvan Pelt , Burkhard Malorny . 2009. Characterization of Pathogenic and Resistant Genome Repertoire Reveals Two ClonalLines in Salmonella enterica subsp. enterica Serovar Paratyphi B (+)-Tartrate Positive. Foodborne Pathogens and Disease6:4, 431-443. [Abstract] [Full Text PDF] [Full Text PDF with Links]

206. Elizabeth Lyon Hannah , James R. Johnson , Frederick Angulo , Bassam Haddadin , Jacquelyn Williamson , Matthew H.Samore . 2009. Molecular Analysis of Antimicrobial-Susceptible and -Resistant Escherichia coli from Retail Meats andHuman Stool and Clinical Specimens in a Rural Community Setting. Foodborne Pathogens and Disease 6:3, 285-295.[Abstract] [Full Text PDF] [Full Text PDF with Links]

207. Helene L Andrews-Polymenis, Carlos A Santiviago, Michael McClelland. 2009. Novel genetic tools for studying food-borneSalmonella. Current Opinion in Biotechnology 20:2, 149-157. [CrossRef]

208. Aaron M. Lynne , Pravin Kaldhone , Donna David , David G. White , Steven L. Foley . 2009. Characterization of AntimicrobialResistance in Salmonella enterica Serotype Heidelberg Isolated from Food Animals. Foodborne Pathogens and Disease 6:2,207-215. [Abstract] [Full Text PDF] [Full Text PDF with Links]

209. K. GAYNOR, S. Y. PARK, R. KANENAKA, R. COLINDRES, E. MINTZ, P. K. RAM, P. KITSUTANI, M. NAKATA,S. WEDEL, D. BOXRUD, D. JENNINGS, H. YOSHIDA, N. TOSAKA, H. HE, M. CHING-LEE, P. V. EFFLER. 2009.International foodborne outbreak of Shigella sonnei infection in airline passengers. Epidemiology and Infection 137:03, 335.[CrossRef]

210. H. C. LEWIS, S. ETHELBERG, K. E. P. OLSEN, E. M. NIELSEN, M. LISBY, S. B. MADSEN, J. BOEL, R. STAFFORD, M.KIRK, H. V. SMITH, S. TIKUMRUM, A. WISETROJANA, A. BANGTRAKULNONTH, J. VITHAYARUNGRUANGSRI,P. SIRIARAYAPORN, K. UNGCHUSAK, J. BISHOP, K. MØLBAK. 2009. Outbreaks of Shigella sonnei infections inDenmark and Australia linked to consumption of imported raw baby corn. Epidemiology and Infection 137:03, 326. [CrossRef]

211. THOMAS G. KINSCHERF, MEE-NGAN YAP, AMY O. CHARKOWSKI, DAVID K. WILLIS. 2009. CHEFPROCEDURES: A RAPID HIGH-TEMPERATURE METHOD FOR SAMPLE PREPARATION, A HIGH VOLTAGEHEPES BUFFER SYSTEM AND THE USE OF NUSIEVE® AGAROSE. Journal of Rapid Methods & Automation inMicrobiology 17:1, 9-16. [CrossRef]

212. Morgane Dominguez , Nathalie Jourdan-Da Silva , Véronique Vaillant , Nathalie Pihier , Cécile Kermin , François-XavierWeill , Gilles Delmas , Annaëlle Kerouanton , Anne Brisabois , Henriette de Valk . 2009. Outbreak of Salmonella entericaSerotype Montevideo Infections in France Linked to Consumption of Cheese Made from Raw Milk. Foodborne Pathogensand Disease 6:1, 121-128. [Abstract] [Full Text PDF] [Full Text PDF with Links]

213. N. De Lappe, G. Doran, J. O'Connor, C. O'Hare, M. Cormican. 2009. Characterization of bacteriophages used in theSalmonella enterica serovar Enteritidis phage-typing scheme. Journal of Medical Microbiology 58:1, 86-93. [CrossRef]

214. Eva Møller Nielsen, Mia Torpdahl, Steen Ethelberg, Anette M. Hammerum. 2009. Variation in Antimicrobial Resistancein Sporadic and Outbreak-related Salmonella enterica Serovar Typhimurium. Emerging Infectious Diseases 15:1, 101-103.[CrossRef]

215. Kara L. F. Cooper, Duncan R. MacCannell, Efrain M. RibotPulsenet: A Program to Detect and Track Food ContaminationEvents . [CrossRef]

216. M. L. Kotewicz, M. K. Mammel, J. E. LeClerc, T. A. Cebula. 2008. Optical mapping and 454 sequencing of Escherichia coliO157 : H7 isolates linked to the US 2006 spinach-associated outbreak. Microbiology 154:11, 3518-3528. [CrossRef]

217. Douglas R. Call , Lisa Orfe , Margaret A. Davis , Stacey Lafrentz , Min-Su Kang . 2008. Impact of Compounding Error onStrategies for Subtyping Pathogenic Bacteria. Foodborne Pathogens and Disease 5:4, 505-516. [Abstract] [Full Text PDF][Full Text PDF with Links] [Supplemental material]

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219. You-Wun Wang, Lih-Ling Chern, Phung Dac Cam, Chien-Shun Chiou. 2008. Evaluation of restriction enzymes forstandardizing pulsed-field gel electrophoresis protocol for rapid subtyping of Vibrio parahaemolyticus. DiagnosticMicrobiology and Infectious Disease 61:3, 251-255. [CrossRef]

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