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Background: Rapid and accurate identification of Verotoxigenic Escherichia coli (VTEC) O157:H7 is dependent on well-established, standardized and highly discriminatory typing methods. Currently, conventional subtyping tests for foodborne bacterial pathogen surveillance are rapidly being replaced with whole-genome sequencing (WGS) in public health laboratories. The capacity of WGS to revolutionize global foodborne disease surveillance has positioned this tool to become the new gold standard; however, to ensure evidence standards for public health decision making can still be achieved, the performance of WGS must be thoroughly validated against current gold standard methods prior to implementation. Here we aim to verify the performance of WGS in comparison to pulsed-field gel electrophoresis (PFGE) and multiple-locus variable-number tandem repeat analysis (MLVA) for eight retrospective outbreaks of VTEC O157:H7 from the Canadian perspective. Since real-time implementation and routine use of WGS in public health laboratories is highly reliant on standardized data analysis tools, we also provide a comparative analysis of two popular methodologies for WGS analyses; an in-house developed single nucleotide variant phylogenomics (SNVPhyl) pipeline and the BioNumerics whole genome multilocus sequence typing (wgMLST) tool. To provide a useful and consistent starting point for examining laboratory-based surveillance data for VTEC O157:H7 in Canada, we also aim to describe the number of genetic differences observed among outbreak-associated isolates. Results: WGS provided enhanced resolution over traditional subtyping methods, and accurately distinguished outbreak-related isolates from non-outbreak related isolates with high epidemiological concordance. WGS also illuminated potential linkages between sporadic cases of illness and contaminated food, and isolates spanning multiple years. The topologies generated by SNVPhyl and wgMLST were highly congruent with strong statistical support. Few genetic differences were observed among outbreak-related isolates (≤5 SNVs/ < 10 wgMLST alleles) unless the outbreak was suspected to be multi-strain. Conclusions: This study validates the superiority of WGS and indicates the BioNumerics wgMLST schema is suitable for surveillance and cluster detection of VTEC O157:H7. These findings will provide a useful and consistent starting point for examining WGS data for prospective laboratory-based surveillance of VTEC O157:H7, but however, the data will continue to be interpreted according to context and in combination with epidemiological and food safety evidence to inform public-health decision making in Canada. [ABSTRACT FROM AUTHOR]

Escherichia coli O157:H7 is a zoonotic pathogen of global importance and the serotype of Shiga toxin-producing E. coli (STEC) most frequently associated with Hemolytic Uremic Syndrome (HUS) in humans. The main STEC reservoir is cattle. Vaccination of calves with the carboxy-terminal fraction of Intimin γ (IntC280) and EspB can reduce E. coli O157:H7 fecal shedding after experimental challenge. Shiga toxin (Stx) exerts local immunosuppressive effects in the bovine intestine and Stx2B fused to Brucella lumazine synthase (BLS-Stx2B) induces Stx2-neutralizing antibodies. To determine if an immune response against Stx could improve a vaccine’s effect on fecal shedding, groups of calves were immunized with EspB + IntC280, with EspB + IntC280 + BLS-Stx2B, or kept as controls. At 24 days post vaccination calves were challenged with E. coli O157:H7. Shedding of E. coli O157:H7 was assessed in recto-anal mucosal swabs by direct plating and enrichment followed by immunomagnetic separation and multiplex PCR. Calves were euthanized 15 days after the challenge and intestinal segments were obtained to assess mucosal antibodies. Vaccination induced a significant increase of IntC280 and EspB specific antibodies in serum and intestinal mucosa in both vaccinated groups. Antibodies against Stx2B were detected in serum and intestinal mucosa of animals vaccinated with 3 antigens. Sera and intestinal homogenates were able to neutralize Stx2 verocytotoxicity compared to the control and the 2-antigens vaccinated group. Both vaccines reduced E. coli O157:H7 shedding compared to the control group. The addition of Stx2B to the vaccine formulation did not result in a superior level of protection compared to the one conferred by IntC280 and EspB alone. It remains to be determined if the inclusion of Stx2B in the vaccine alters E. coli O157:H7 shedding patterns in the long term and after recurrent low dose exposure as occurring in cattle herds. [ABSTRACT FROM AUTHOR]

Healthy cattle are the primary reservoir for O157:H7 Shiga toxin-producing E. coli responsible for human food-borne infections. Because farm environment acts as a source of cattle contamination, it is important to better understand the factors controlling the persistence of E. coli O157:H7 outside the bovine gut. The E. coli O157:H7 strain MC2, identified as a persistent strain in French farms, possessed the characteristics required to cause human infections and genetic markers associated with clinical O157:H7 isolates. Therefore, the capacity of E. coli MC2 to survive during its transit through the bovine gastro-intestinal tract (GIT) and to respond to stresses potentially encountered in extra-intestinal environments was analyzed. E. coli MC2 survived in rumen fluids, grew in the content of posterior digestive compartments and survived in bovine feces at 15°C predicting a successful transit of the bacteria along the bovine GIT and its persistence outside the bovine intestine. E. coli MC2 possessed the genetic information encoding 14 adherence systems including adhesins with properties related to colonization of the bovine intestine (F9 fimbriae, EhaA and EspP autotransporters, HCP pilus, FdeC adhesin) reflecting the capacity of the bacteria to colonize different segments of the bovine GIT. E. coli MC2 was also a strong biofilm producer when incubated in fecal samples at low temperature and had a greater ability to form biofilms than the bovine commensal E. coli strain BG1. Furthermore, in contrast to BG1, E. coli MC2 responded to temperature stresses by inducing the genes cspA and htrA during its survival in bovine feces at 15°C. E. coli MC2 also activated genes that are part of the GhoT/GhoS, HicA/HicB and EcnB/EcnA toxin/antitoxin systems involved in the response of E. coli to nutrient starvation and chemical stresses. In summary, the large number of colonization factors known to bind to intestinal epithelium and to biotic or abiotic surfaces, the capacity to produce biofilms and to activate stress fitness genes in bovine feces could explain the persistence of E. coli MC2 in the farm environment. [ABSTRACT FROM AUTHOR]

Background and Objective: Enterohemorrhagic Escherichia coli is a pathogen that can be transmitted to humans through food products and causes dangerous diseases such as hemorrhagic colitis and hemolytic uremic syndrome in humans because of shiga toxin production. Materials and Method: In this research, 256 samples of fresh vegetables including lettuce, cabbage and eating herbs were prepared from 4 vegetable wholesale centers in the city of Ahvaz during 8 months. After primary enrichment, Sorbitol negative colonies grown on CT-SMAC medium were subcultured on differential culture media and confirmed as E. coli by specific biochemical tests. Confirmed strains were then investigated by E.coli O157:H7 antiserum. Finally, the presence of stx2, stx1, eaeA and hlyA genes was evaluated in sorbitol negative strains using multiplex PCR. Result: 8 E.coli O157 (3.1%) bacteria were detected, only 2 isolates were identified as E.coli O157:H7. After multiplex PCR it became clear that 4 isolates contained stx1 gene, 2 isolates stx2 gene, 1 isolate stx1 and eaeA genes, 1 isolate stx1, eaeA and hlyA genes and 1 isolate stx1 and hlyA genes. None of the isolates contained all four genes. Conclusion: The presence of E.coli bacteria in vegetables is problematic for public health and can cause food-borne diseases. [ABSTRACT FROM AUTHOR]

There are several anecdotal reports of insertion sequence (IS) element inactivation of verotoxin genes among enterohaemorrhagic Escherichia coli of the serotype O157:H7, a pathogen causing severe gastrointestinal disease in infected humans. These insertions can be expected to drastically reduce the virulence of the bacteria. IS element inactivation has been shown to be reversible in model systems, suggesting the possibility of spontaneous restoration of virulence. In this study, traditional and high-throughput sequencing was used to characterise three patterns of IS629 inactivation of verotoxin 2 genes in EHEC O157:H7, caused by insertion or insertion followed by partial deletion. At least one of the patterns of inactivation appears to have persisted several years among cattle O157:H7, indicating it has no major effect on fitness in the animal reservoir. Digital PCR was used to directly quantify the reversal rates of the insertional inactivation of a selected isolate under laboratory conditions. Inserts were found to be absent from in the order of 1/105 of individual genomes, with significantly higher loss frequencies observed in cultures under nutrient-poor conditions. We conclude that strains with this type of inactivation found in food or animal samples should be considered a threat to human health, and may pose a challenge for PCR-based detection methods. [ABSTRACT FROM AUTHOR]

The authors report on a rapid voltammetric method for simultaneous determination of the pathogens E. coli and Salmonella typhimurium ( S. typh.) by detecting the rfbE gene of E. coli O157:H7 and gyrB gene of S. typh., respectively, and by using polymerase-assisted target recycling amplification. The assay was constructed by self-assembly of the respective hairpin probes (labeled with the electrochemical probes Methylene Blue and ferrocene) on the surface of a gold electrode. After hybridization between target DNA and hairpin probes (HPs) has occurred, the primers hybridize with the open-chain HPs and initiate extension reactions in the presence of polymerase and deoxyribonucleoside triphosphates. This results in the release of the redox labels from the electrode surface and the target dissociating from the HPs. The released target will bind to other HPs to activate new cycles, which results in enhanced suppression of current, measured best at −0.27 V and +0.36 V (vs. Ag/AgCl) for parallel detection of E. coli DNA and S. typh. DNA, respectively. The method presented here based on target recycling amplification and its integration into multiplexed electrochemical detection of pathogens was successfully applied to quantitative determination of E. coli O157:H7 and S. typh. in synthetic samples. In our perception, the strategy presented here represents a rapid and universal platform for sensitive and multiplexed quantitation of pathogens and related molecular diagnostic targets of relevance in food safety control. [ABSTRACT FROM AUTHOR]

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 (O157) is one of the most notorious human pathogens, causing severe disease in humans worldwide. O157 specifically colonizes the large intestine of mammals after passing through the small intestine, and this process is influenced by differential signals between the two regions. Small regulatory RNAs (sRNAs) are able to sense and respond to environmental changes and regulate diverse physiological processes in pathogenic bacteria. Although some sRNAs of O157 have been extensively investigated, whether these molecules can sense differences between the small and large intestine and influence the preferential colonization in the large intestine by O157 remains unknown. In this study, we identified a new sRNA, Esr055, in O157 which senses the low DNA concentration in the large intestine and contributes to the preferential colonization of the bacteria in this region. The number of O157 wild-type that adhered to the colon is 30.18 times higher than the number that adhered to the ileum of mice, while the number of the 1Esr055 mutant that adhered to the colon decreased to 13.27 times higher than the number adhered to the ileum. Furthermore, we found that the expression of Esr055 is directly activated by the regulator, DeoR, and its expression is positively affected by DNA, which is significantly more abundant in the ileum than in the colon of mice. Additionally, combining the results of informatics predictions and transcriptomic analysis, we found that several virulence genes are up-regulated in the ΔEsr055 mutant and five candidate genes (z0568, z0974, z1356, z1926, and z5187) may be its direct targets. [ABSTRACT FROM AUTHOR]

Verotoxin-producing E. coli (VTEC) O157:H7 is the dominant serotype isolated from patients with HUS and, Argentina has the highest rate of HUS in the world. Molecular typing had allowed to identify subpopulations related to the origin and virulence of O157:H7 strains. Our aim was to perform a genetic characterization of 43 O157:H7 strains isolated in Argentine mostly from cattle and humans in order to establish the potential public health risk. For it, we used a combination of molecular subtyping methods in order to identify clade 8_ rhsA ( C3468G ), LSPA-6 and virulence profiles and, a cytotoxicity assay on Vero cell. All isolates carried the clade 8 SNP variant and 98% of them belonged to lineage I/II (2% lineage II). Isolates were grouped into eleven nle profiles, 46% were positive for all nle genes, while the remaining isolates, except two, showed incomplete OI-71, particularly lacked nleF . All isolates showed the plasmid profile ehxA-espP-katP-stcE and harbored ehaA , elfA , iha and l pfA variants lpfA1-3 and lpfA2-2 and, ECSP_0242. The frequencies of the remaining ECSP genes were 95% ECSP_2687, 88% ECSP_3286, 86% ECSP_3620, 53% ECSP_2870/2872 and 44% ECSP_1733. All O157:H7 strains, except the isolate identified as lineage II, were cytotoxic on Vero cells. Among Argentinean strains, most genetic markers occur at equal relative frequencies among clinical and bovine isolates, showing diversity mostly in nle genes profiles. The belonging of the isolates to hypervirulent clade 8 and lineage I/II, the high prevalence of nle and putative virulence factors genes, would allow assigning most O157:H7 strains of this region a high risk to public health. [ABSTRACT FROM AUTHOR]

We previously reported that the strains of Escherichia coli O157:H7 (EcO157) that survived longer in austere soil environment lacked expression of curli, a fitness trait linked with intestinal colonization. In addition, the proportion of curli-positive variants of EcO157 decreased with repeated soil exposure. Here we evaluated 84 and 176 clinical strains from outbreaks and sporadic infections in the US, plus 211 animal fecal and environmental strains for curli expression. These shiga-toxigenic strains were from 328 different genotypes, as characterized by multi-locus variable-number tandem-repeat analysis (MLVA). More than half of the fecal strains (human and animal) and a significant proportion of environmental isolates (82%) were found to lack curli expression. EcO157 strains from several outbreaks linked with the consumption of contaminated apple juice, produce, hamburgers, steak and beef were also found to lack curli expression. Phylogenetic analysis of fecal strains indicates curli expression is distributed throughout the population. However, a significant proportion of animal fecal isolates (84%) gave no curli expression compared to human fecal isolates (58%). In addition, analysis of environmental isolates indicated nearly exclusive clustering of curli expression to a single branch of the minimal spanning tree. This indicates that curli expression depends primarily upon the type of environmental exposure and the isolation source, although genotypic differences also contribute to clonal variation in curli. Furthermore, curli-deficient phenotype appears to be a selective trait for survival of EcO157 in agricultural environments.

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne diarrheal illness in the United States and globally, and serotype O157:H7 is frequently associated with STEC outbreaks and sporadic cases in the United States. Severe systemic diseases associated with STEC are mediated by Stx types, particularly subtype Stx2a, encoded on inducible bacteriophages. We previously identified two STEC O157:H7 clinical isolates, JH2010 and JH2012, that exhibit a large difference in virulence in a streptomycin (Str)-treated mouse model. In this study, we aimed to identify a genetic basis for the difference in virulence between those strains. Comparison of the stx 2a phage sequences showed that JH2012 lacks the lytic genes S and R on the phage genome. We also demonstrated that compared to JH2012 cultures, cultures of JH2010 released more Stx2 into the supernatant and were more sensitive to bacterial lysis during growth with ciprofloxacin (Cip), an inducer of stx phages. We therefore generated an stx 2a genes from the stx2a phage in JH2010, and another O157:H7 strain, JH2016, resulted in increased cellular retention of Stx2, but there was no difference in virulence compared to the wild-type strains. Our results indicate that the SR deletion mutant strain of JH2010 to determine if those genes were responsible for the high virulence of that strain. We found that deletion of the SR genes from the stx2a phage in JH2010, and another O157:H7 strain, JH2016, resulted in increased cellular retention of Stx2, but there was no difference in virulence compared to the wild-type strains. Our results indicate that the stx 2a phage SR phage lytic genes are not required for the virulence of pathogenic O157:H7 clinical isolates in a murine model of STEC infection or for release of Stx2a into the supernatant of bacterial cultures. These results point to an alternate mechanism for Stx2a release from STEC strains.in vitro but that they are not required in wild-type STEC strains for virulence in a mouse model. IMPORTANCE The release of Stx from STEC has been thought to be tied to phage-mediated lysis of the host bacterial cell. In this study, we found that the stx 2a phage lytic genes are not required for the virulence of pathogenic O157:H7 clinical isolates in a murine model of STEC infection or for release of Stx2a into the supernatant of bacterial cultures. These results point to an alternate mechanism for Stx2a release from STEC strains., Competing Interests: The authors declare no conflict of interest.

Escherichia coli O157:H7 is a foodborne pathogen implicated in numerous outbreaks worldwide that has the ability to cause extra-intestinal complications in humans. The Enteropathogens Division of the Central Public Health Laboratory (CPHL) in Paraguay is working to improve the genomic characterization of Shiga toxin-producing E. coli (STEC) to enhance laboratory-based surveillance and investigation of foodborne disease outbreaks. Whole genome sequencing (WGS) is proposed worldwide to be used in the routine laboratory as a high-resolution tool that allows to have all the results in a single workflow. This study aimed to carry out for the first time, the genomic characterization by WGS of nine STEC O157:H7 strains isolated from human samples in Paraguay. We were able to identify virulence and resistance mechanisms, MLST subtype, and even establish the phylogenetic relationships between isolates. Furthermore, we detected the presence of strains belonging to hypervirulent clade 8 in most of the isolates studied., (Copyright © 2022 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.)

Background&Objective: Shiga-toxin producing E. coli (STEC) belonging to several different O serotypes are one of the etiological agent of diarrhea. The STEC strains are considered as an etiological agent for enteritis after non-typhoidal salmonellosis and Campylobacter. They have also been associated closely with the hemolytic uremic syndrome (HUS) and hemorrhagic colitis(HC). The aim of this study was to determine of the frequency of STEC in patients with hemorrhagic colitis referring to Tehran hospitals. Materials&Methods: From March to September 2004, 70 patients with hemorrhagic colitis (Case)an 70 patients with diarrhea (Control) were included in this study. The stx gene was detected by PCR and was used for the determination of STEC strains. Slide agglutination with specific antisera used to detect O serogroup. Polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP) analysis of the flagellin gene (fliC) was performed for determining their flagellar antigen (H). Results: Two samples (2.9%) from Hemorrhagic colitis cases and 12 samples (17.1 %) from diarrheal cases were positive for STEC. There was no significant correlation between STEC and Hemorrhagic colitis but there was a significant correlation between STEC and diarrhea (p

We previously reported that the strains of Escherichia coli O157:H7 (EcO157) that survived longer in austere soil environment lacked expression of curli, a fitness trait linked with intestinal colonization. In addition, the proportion of curli-positive variants of EcO157 decreased with repeated soil exposure. Here we evaluated 84 and 176 clinical strains from outbreaks and sporadic infections in the US, plus 211 animal fecal and environmental strains for curli expression. These shiga-toxigenic strains were from 328 different genotypes, as characterized by multi-locus variable-number tandem-repeat analysis (MLVA). More than half of the fecal strains (human and animal) and a significant proportion of environmental isolates (82%) were found to lack curli expression. EcO157 strains from several outbreaks linked with the consumption of contaminated apple juice, produce, hamburgers, steak, and beef were also found to lack curli expression. Phylogenetic analysis of fecal strains indicates curli expression is distributed throughout the population. However, a significant proportion of animal fecal isolates (84%) gave no curli expression compared to human fecal isolates (58%). In addition, analysis of environmental isolates indicated nearly exclusive clustering of curli expression to a single branch of the minimal spanning tree. This indicates that curli expression depends primarily upon the type of environmental exposure and the isolation source, although genotypic differences also contribute to clonal variation in curli. Furthermore, curli-deficient phenotype appears to be a selective trait for survival of EcO157 in agricultural environments. [ABSTRACT FROM AUTHOR]

Escherichia coli O157:H7 is an enteric pathogen associated with food safety threats and with significant morbidity and mortality worldwide. In Argentina, post-enteric hemolytic uremic syndrome (HUS) is endemic, with > 70% of cases associated with E. coli O157 infection. To date the biological basis behind the severity among E. coli O157 infections is unknown. However, single nucleotide polymorphism (SNP) typing has helped to define nine E. coli O157:H7 clades, of which clade 8 strains are associated with severe disease cases. The aim of this study was to characterize a collection of 20 STEC O157:H7 strains isolated between 2011 and 2013 from ground beef and different environmental samples from butcher shops of Argentina. All strains harbored the eae , ehx A, fli C H7 , efa , iha , and tox B genes, with stx 2a / stx 2c as the predominant genotype (75%). The Xba I-PFGE analysis showed that the E. coli O157 strains had high genetic diversity. Nine strains were grouped in four Xba I-PFGE clusters, whereas 11 strains showed unique Xba I-PFGE patterns. In contrast, the SNP analysis allowed us to separate the strains in two distinct lineages representing clade 8 (70%) and clade 6 (30%). Our results show the molecular characterization of E. coli O157 strains isolated from ground beef and environmental samples from Argentinean butcher shops. [ABSTRACT FROM AUTHOR]

High variability in the expression of csgD-dependent, biofilm-forming and adhesive properties is common among Shiga toxin-producing Escherichia coli. Although many strains of serotype O157:H7 form little biofilm, conversion to stronger biofilm phenotypes has been observed. In this study, we screened different strains of serotype O157:H7 for the emergence of strong Congo-red (CR) affinity/biofilm-forming properties and investigated the underlying genetic mechanisms. Two major mechanisms which conferred stronger biofilm phenotypes were identified: mutations (insertion, deletion, single nucleotide change) in rcsB region and stx-prophage excision from the mlrA site. Restoration of the native mlrA gene (due to prophage excision) resulted in strong biofilm properties to all variants. Whereas RcsB mutants showed weaker CR affinity and biofilm properties, it provided more possibilities for phenotypic presentations through heterogenic sequence mutations. [ABSTRACT FROM AUTHOR]

Escherichia coli O157:H7 is an enterohemorrhagic E. coli (EHEC) strain and a major food-borne pathogen, causing severe disease in humans worldwide. Multiple sensitive, accurate, and quantitative methods are needed to provide a comprehensive analysis of cell damage caused by O157:H7. However, the current, universally adopted methods for O157:H7 virulence assessment fail to investigate the interactive effects of O157:H7 and its host cells, neglect the effects of infection of host cells by O157:H7, and fail to comprehensively and accurately reflect the true pathogenicity of O157:H7. In this study, three different accurate, sensitive, and quantifiable methods were supplementary to provide standard operating procedures to analyze the cytotoxicity of O157:H7. This set of methods can be applied to toxicity studies of newly discovered O157:H7 clinical isolates and used to study how a clinical isolate's toxicity correlates with its pathogenicity. These methods can also be used in future studies of latent virulence factors and to explore the pathogenic mechanisms of O157:H7. [ABSTRACT FROM AUTHOR]

Enterohemorrhagic Escherichia coli, including the serotype O157:H7 that is most commonly identified with human disease, cause both sporadic cases and outbreaks of non-bloody diarrhea and hemorrhagic colitis. In about 10% of infected subjects, the hemolytic uremic syndrome (hemolytic anemic, thrombocytopenia, and acute renal failure) develops, likely as a consequence of systemic spread of bacterial-derived toxins variously referred to as Shiga-like toxin, Shiga toxin, and Verotoxin. Increasing evidence points to a complex interplay between bacterial products - for example, adhesins and toxins - and host signal transduction pathways in mediating responses to infection. Identification of critical signaling pathways could result in the development of novel strategies for intervention to both prevent and treat this microbial infection in humans.

Shiga toxin-producing Escherichia coli (STEC) and Salmonella are food-borne pathogens commonly associated with beef, and reliable methods are needed to determine their prevalence in beef and to ensure food safety. Retail ground beef was tested for the presence of E. coli O157:H7, STEC serogroups O26, O45, O103, O111, O121, and O145, and Salmonella using the DuPont™ BAX® system method. Ground beef (325 g) samples were enriched in 1.5 L of TSB with 2 mg/L novobiocin at 42°C for 18 h, and then evaluated using the BAX® System real-time PCR assays for E. coli O157:H7 and STEC suite, and the BAX® System standard PCR assays for E. coli O157:H7 MP and Salmonella. Samples positive for STEC target genes by the BAX® System assays were subjected to immunomagnetic separation (IMS) and plating onto modified Rainbow Agar O157. Enrichments that were PCR positive for Salmonella were inoculated into RV broth, incubated for 18 h at 42C, and then plated onto XLT-4 agar. Presumptive positive STEC and Salmonella colonies were confirmed using the BAX® System assays. Results of the BAX® System STEC assays showed 20/308 (6.5%) of samples positive for both the Shiga toxin (stx) and intimin (eae) genes; 4 (1.3%) for stx, eae, and O26; 1 (0.3%) for stx, eae, and O45; 3 (1%) for stx, eae, and O103; and 1 (0.3%) for stx, eae, and O145. There were also 3 samples positive for stx, eae, and more than one STEC serogroup. Three (1.0%) of the samples were positive using the BAX® System real-time E. coli O157:H7 assay, and 28 (9.1%) were positive using the BAX® System Salmonella assay. STEC O103 and E. coli O157:H7 were isolated from 2/6 and 2/3 PCR positive samples, respectively. Salmonella isolates were recovered and confirmed from 27 of the 28 Salmonella PCR positive samples, and a portion of the isolates were serotyped and antibiotic resistance profiles determined. Results demonstrate that the BAX® System assays are effective for detecting STEC and Salmonella in beef.

A multistate outbreak of Escherichia coli O157:H7 infections occurred in the United States in June and July 1997. Two concurrent outbreaks were investigated through independent case-control studies in Michigan and Virginia and by subtyping isolates with pulsed-field gel electrophoresis (PFGE). Isolates from 85 persons were indistinguishable by PFGE. Alfalfa sprouts were the only exposure associated with E. coli O157:H7 infection in both Michigan and Virginia. Seeds used for sprouting were traced back to one common lot harvested in Idaho. New subtyping tools such as PFGE used in this investigation are essential to link isolated infections to a single outbreak.

Escherichia coli O157 is an important food-borne pathogen that can cause diarrhoea, haemorrhagic colitis, and haemolytic uraemic syndrome. The aim of this study was to investigate the prevalence, virulence genes, antibiotic resistance, and genetic diversity of E. coli O157 and O157:H7 in retail fresh raw meat sold in the markets of South China. Of 551 samples collected, 21 (3.81 %) were contaminated with E. coli O157 and seven (1.27 %) with O157:H7. The highest prevalence rate was found in beef (13.32 %), followed by pork (6.90 %), chicken (3.28 %), duck (2.54 %), and mutton (0). The virulence genes stx 1, stx2, eaeA, and hlyA were detected in 10.71, 21.43, 85.71, and 25 % of 28 isolates, respectively. The isolates were highly resistant to penicillin (100 %), chloramphenicol (64.29 %), ampicillin (57.14 %), and sensitive to gentamicin (100 %), cefotazidime (96.43 %), and ciprofloxacin (96.43 %). Enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) classified 28 isolates and two reference strains into 19 different profiles with a discrimination index (D) of 0.961. Four E. coli O157:H7 isolates from beef showed 83 % similarity with the two clinical reference strains, indicating a potential high virulence for consumers. The results of this study suggested that fresh raw meat could be potential vehicles for transmission of E. coli O157 to humans. [ABSTRACT FROM AUTHOR]

Background: Shiga toxin (Stx)-producing E. coli (STEC) are responsible for foodborne outbreaks that can result in severe human disease. During an outbreak, differential disease outcomes are observed after infection with the same STEC strain. One question of particular interest is why some infected people resolve infection after hemorrhagic colitis whereas others progress to the hemolytic uremic syndrome (HUS). Host age and infection dose have been implicated; however, these parameters do not appear to fully account for all of the observed variation in disease severity. Therefore, we hypothesized that additional host genetic factors may play a role in progression to HUS. Methods and Results: To mimic the genetic diversity in the human response to infection by STEC, we measured the capacity of an O157:H7 outbreak isolate to colonize mouse strains from the advanced recombinant inbred (ARI) BXD panel. We first infected the BXD parental strains C57BL/6 J (B6) and DBA/2 J (D2) with either 86-24 (Stx2a+) or TUV86-2, an Stx2a-negative isogenic mutant. Colonization levels were determined in an intact commensal flora (ICF) infection model. We found a significant difference in colonization levels between the parental B6 and D2 strains after infection with TUV86-2 but not with 86-24. This observation suggested that a host factor that may be masked by Stx2a affects O157:H7 colonization in some genetic backgrounds. We then determined the TUV86-2 colonization levels of 24 BXD strains in the ICF model. We identified several quantitative trait loci (QTL) associated with variation in colonization by correlation analyses. We found a highly significant QTL on proximal chromosome 9 (12.5-26.7 Mb) that strongly predicts variation in colonization levels and accounts for 15-20 % of variance. Linkage, polymorphism and co-citation analyses of the mapped region revealed 36 candidate genes within the QTL, and we identified five genes that are most likely responsible for the differential colonization. Conclusions: The identification of the QTL on chromosome 9 supports our hypothesis that individual genetic makeup affects the level of colonization after infection with STEC O157:H7. [ABSTRACT FROM AUTHOR]

It has been earlier hypothesized that lysogenic infection with Stx-encoding phages influences protein expression in the bacterial host, and therefore, some differentially expressed proteins could affect survival characteristics and pathogenicity. We compared the protein expression profiles of the host MG1655 and lysogens by 2D electrophoresis. Four different genes identified were all related to Fe/S subunit production, namely, nfuA, fdoH, sdhB and ftnA. To explore the role of nfuA in the biology of Stx prophage lysogeny, gene knockout experiments and phage lysogenic conversion were performed. The inactivation of nfuA caused the prophage to enter its lytic life cycle, especially under an iron-depleted condition. A similar activity was also detected in the Escherichia coli O157:H7 strain from which the Stx phage Min 27 was originally isolated. NfuA might be the positive regulator of genes controlling lysogenic cycle such as cI, cII and cIII since their transcriptional level was significantly reduced in nfuA deletion mutant as shown by qRT-PCR. We conclude that NfuA is essential for maintenance of Stx phage lysogeny in host's genetic reservoir under iron-deficient condition. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) O157:H7 is an important food-borne pathogen that has been implicated in numerous disease outbreaks worldwide. Little is known about the extent and molecular basis of antimicrobial resistance in STEC O157:H7 of food origin. Therefore, the current study aimed to characterize the genetic basis of multidrug resistance in 54 STEC O157:H7 strains isolated from 1600 food samples (800 meat products and 800 dairy products) collected from different street venders, butchers, retail markets, and slaughterhouses in Egypt. Thirty-one of 54 (57.4%) isolates showed multidrug resistance phenotypes to at least three classes of antimicrobials. The highest incidence of antimicrobial resistance was to kanamycin (96.8%), followed by spectinomycin (93.6%), ampicillin (90.3%), streptomycin (87.1%), and tetracycline (80.6%). PCR and DNA sequencing were used to screen and characterize integrons and antibiotic resistance genes, and 29.6% and 5.6% of isolates were positive for class 1 and class 2 integrons, respectively. β-Lactamase-encoding genes were identified in 63.0% of isolates as follows: bla TEM-1 and bla TEM-52 in 35.2% and 1.9% isolates respectively; bla CMY-2 in 13.0% isolates; bla CTX-M in 5.6% isolates; bla SHV-12 in 5.6% isolates; and bla OXA-1 in 1.9% isolate. The plasmid-mediated quinolone resistance genes were identified in 13.0% of isolates as follows: qnrB , qnrS , and aac ( 6 ′)- Ib - cr in 5.6%, 3.7%, and 3.7% isolates, respectively. Finally, the florfenicol resistance gene floR was identified in 7.4% of isolates. This study demonstrated that meat and dairy products are potential sources of multidrug resistant STEC O157:H7. To our knowledge, this is the first report of the occurrence of class 2 integrons, qnrB , qnrS , and aac ( 6 ′)- Ib - cr in STEC O157:H7. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC), and especially enterohaemorrhagic E. coli (EHEC) are important, highly virulent zoonotic and food-borne pathogens. The genes encoding their key virulence factors, the Shiga toxins, are distributed by converting bacteriophages, the Stx phages. In this study we isolated a new type of inducible Stx phage carrying the stx1 gene cluster from the prototypic EHEC O157:H7 Sakai strain. The phage showed Podoviridae morphology, and was capable of converting the E. coli K-12 MG1655 strain to Shiga toxin-producing phenotype. The majority of the phage genes originate from the stx2 -encoding Sakai prophage Sp5, with major rearrangements in its genome. Beside certain minor recombinations, the genomic region originally containing the stx2 genes in Sp5 was replaced by a region containing six open reading frames from prophage Sp15 including stx1 genes. The rearranged genome, together with the carriage of stx1 genes, the morphology and the capability of lysogenic conversion represent a new type of recombinant Stx1 converting phage from the Sakai strain. [ABSTRACT FROM AUTHOR]

Background Zinc supplements can treat or prevent enteric infections and diarrheal disease. Many articles on zinc in bacteria, however, highlight the essential nature of this metal for bacterial growth and virulence, suggesting that zinc should make infections worse, not better. To address this paradox, we tested whether zinc might have protective effects on intestinal epithelium as well as on the pathogen. Results Sing polarized monolayers of T84 cells we found that zinc protected against damage induced by hydrogen peroxide, as measured by trans-epithelial electrical resistance. Zinc also reduced peroxide-induced translocation of Shiga toxin (Stx) across T84 monolayers from the apical to basolateral side. Zinc was superior to other divalent metals to (iron, manganese, and nickel) in protecting against peroxide-induced epithelial damage, while copper also showed a protective effect. The SOS bacterial stress response pathway is a powerful regulator of Stx production in STEC. We examined whether zinc's known inhibitory effects on Stx might be mediated by blocking the SOS response. Zinc reduced expression of recA, a reliable marker of the SOS. Zinc was more potent and more efficacious than other metals tested in inhibiting recA expression induced by hydrogen peroxide, xanthine oxidase, or the antibiotic ciprofloxacin. The close correlation between zinc's effects on recA/SOS and on Stx suggested that inhibition of the SOS response is one mechanism by which zinc protects against STEC infection. Conclusions Zinc's ability to protect against enteric bacterial pathogens may be the result of its combined effects on host tissues as well as inhibition of virulence in some pathogens. Research focused solely on the effects of zinc on pathogenic microbes may give an incomplete picture by failing to account for protective effects of zinc on host epithelia. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) and Salmonella are food-borne pathogens commonly associated with beef, and reliable methods are needed to determine their prevalence in beef and to ensure food safety. Retail ground beef was tested for the presence of E. coli O157:H7, STEC serogroups O26, O45, O103, O111, O121, and O145, and Salmonella using the DuPont™ BAX®system method. Ground beef (325 g) samples were enriched in 1.5 L of TSB with 2 mg/L novobiocin at 42°C for 18 h, and then evaluated using the BAX® System real-time PCR assays for E. coliO157:H7 and STEC suite, and the BAX® System standard PCR assays for E. coli O157:H7 MP andSalmonella. Samples positive for STEC target genes by the BAX® System assays were subjected to immunomagnetic separation (IMS) and plating onto modified Rainbow Agar O157. Enrichments that were PCR positive for Salmonella were inoculated into RV broth, incubated for 18 h at 42°C, and then plated onto XLT-4 agar. Presumptive positive STEC and Salmonella colonies were confirmed using the BAX® System assays. Results of the BAX® System STEC assays showed 20/308 (6.5%) of samples positive for both the Shiga toxin (stx) and intimin (eae) genes; 4 (1.3%) for stx, eae, and O26; 1 (0.3%) for stx, eae, and O45; 3 (1%) for stx, eae, and O103; and 1 (0.3%) for stx, eae, and O145. There were also 3 samples positive for stx, eae, and more than one STEC serogroup. Three (1.0%) of the samples were positive using the BAX® System real-time E. coli O157:H7 assay, and 28 (9.1%) were positive using the BAX® System Salmonella assay. STEC O103 and E. coli O157:H7 were isolated from 2/6 and 2/3 PCR positive samples, respectively. Salmonella isolates were recovered and confirmed from 27 of the 28 Salmonella PCR positive samples, and a portion of the isolates were serotyped and antibiotic resistance profiles determined. Results demonstrate that the BAX® System assays are effective for detecting STEC and Salmonella in beef. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) causes serious human illness such as hemolytic uremic syndrome (HUS). Argentina has the world’s highest rate of this syndrome, which is the leading cause of acute renal failure among children. E. coli O157:H7 is the most common cause of HUS, but a substantial and growing proportion of this illness is caused by infection due to non- O157 strains. Multiple-locus variable-number tandem repeat analysis (MLVA) has become an established technique to subtype STEC. This review will address the use of routine STEC subtyping by MLVA in order to type this group of isolates and to get insight into the genetic diversity of native STEC. With regard to these objetives we modified and adapted two MLVA protocols, one exclusive for O157 and the other, a generic E. coli assay. A total of 202 STEC isolates, from different origin and corresponding to 20 serotypes, have been MLVA genotyped in our laboratory. In our experience, MLVA works well at our laboratory and enables us to perform an efficient STEC subtyping. The diversity found in many serotypes may be useful for future epidemiological studies of STEC strains, belonging to O157 as well as to non-O157 serogroups.

Shiga-toxigenic Escherichia coli (STEC) O157:H7 uses a myriad of surface adhesive appendages including pili, flagella, and the type 3 secretion system (T3SS) to adhere to and inflict damage to the human gut mucosa. Consumption of contaminated ground beef, milk, juices, water or leafy greens has been associated with outbreaks of diarrheal disease in humans due to STEC. The aim of this study was to investigate which of the known STEC O157:H7 adherence factors mediate colonization of baby spinach leaves and where the bacteria reside within tainted leaves. We found that STEC O157:H7 colonizes baby spinach leaves through the coordinated production of curli, the E. coli common pilus (ECP), hemorrhagic coli type 4 pilus (HCP), flagella, and T3SS. Electron microscopy analysis of tainted leaves revealed STEC bacteria in the internal cavity of the stomata, in intercellular spaces, and within vascular tissue (xylem and phloem), where the bacteria were protected from the bactericidal effect of gentamicin, sodium hypochlorite or ozonated water treatments. We confirmed that the T3S escN mutant showed a reduced number of bacteria within the stomata suggesting that T3S is required for the successful colonization of leaves. In agreement, non-pathogenic E. coli K-12 strain DH5α transformed with a plasmid carrying the LEE pathogenicity island, harboring the T3SS and effector genes, internalized into stomata more efficiently than without the LEE. This study highlights a role for pili, flagella, and T3SS in the interaction of STEC with spinach leaves. Colonization of plant stomata and internal tissues may constitute a strategy by which STEC survives in a nutrient-rich microenvironment protected from external foes and may be a potential source for human infection.

Abstract: Sorbitol-fermenting (SF) Escherichia coli O157:H- strains have emerged as important pathogens and have been associated with a higher incidence of progression to hemolytic–uremic syndrome (HUS) than non-sorbitol fermenting (NSF) E. coli O157:H7. The present study was carried out to determine the prevalence of SF E. coli O157:H- and NSF E. coli O157:H7 strains in retail beef products in Mansoura, Egypt. The contamination rates with rfbE O157-positive E. coli O157 strains were 26.7% (8/30), 10% (3/30) and 3.7% (1/27) in ground beef, beef burger, and fresh beef samples, respectively with an overall mean of 13.8% (12/87) among all meat products tested. SF E. coli O157:H- were the most dominant among the isolated O157 strains. Of the fifteen O157 strains isolated, 11 (73.3%) were SF E. coli O157:H-, while the remaining 4 (26.7%) were NSF E. coli O157:H7. The 11 SF O157H- strains were genetically positive for sfpA gene. Restriction fragment length polymorphism (RFLP) analysis for fliC gene demonstrated a similar pattern for both SF and NSF O157 isolates. PCR assays verified the existence of stx1 gene in 7 (46.7%) and stx2 gene in 13 (86.7%) of the 15 O157 strains isolated. Unexpectedly, two of the 15 O157 strains isolated were negative for Shiga toxin genes. The eae gene was identified in all of the 15 O157 strains except in one NSF O157:H7 strain. EHEC-hlyA gene was detected in 14 (93.3%) of the 15 O157 isolates, nonetheless only 11 strains showed enterohemolytic phenotype on blood agar. A combination of the four virulence genes, stx1, stx2, eae and EHEC-hlyA were detected in 7 (46.7%) strains, while six (40%) strains were positive for stx2, eae and hlyA genes. This is the first record for isolation of E. coli O157: H- in Egypt as well as in the African continent. [Copyright &y& Elsevier]

Meat is the main vehicle for food poisoning as a result of poor hygiene in the slaughtering of animals or during the handling of carcasses. This study analyzes three municipal slaughterhouses of the Central Mexican Plateau. Two hundred and twenty eight paired samples were obtained from carcasses (n= 114) and colon content (n= 114) of cattle slaughtered at these abattoirs. Two (0.8 %) E. coli O157: NM strains from colon content and 6 (2.6 %) E. coli O157: H7 strains (5 carcasses and 1 colon content) were found. The percentage of isolation from each slaughterhouse was variable, finding significant differences (P<0.05). In E. coli O157: NM and O157: H7 strains, it was observed that the highest resistance to cephalothin was 75 %, 62.5 % carbenicillin, 50 % amikacin and 50 % gentamicin. E. coli O157: H7 strains presented 16.7 % of the eae gene, 16.7 % eae, stx1 and stx2 genes and 66.7 % eae and stx2 genes. In conclusion the results obtained show the presence of E. coli O157: H7 virulence factors and antibiotic resistance in cattle carcasses of the Central Mexican Plateau, which is considered a major source of contamination and a public health risk. [ABSTRACT FROM AUTHOR]

Background Escherichia coli O157 (E. coli O157) has been isolated from bison retail meat, a fact that is important given that bison meat has been implicated in an E. coli O157-multistate outbreak. In addition, E. coli O157 has also been isolated from bison feces at slaughter and on farms. Cattle are well documented as E. coli O157 reservoirs, and the primary site of E. coli O157 persistence in such reservoirs is the rectoanal junction (RAJ), located at the distal end of the bovine gastrointestinal tract. Since bison and cattle share many genetic similarities manifested as common lineage, susceptibility to infection and the nature of immune responses to infectious agents, we decided to evaluate whether the RAJ of these animals were comparable both in terms of cellular architecture and as sites for adherence of E. coli O157. Specifically, we compared the histo-morphologies of the RAJ and evaluated the E. coli O157 adherence characteristics to the RAJ squamous epithelial (RSE) cells, from these two species. Results We found that the RAJ of both bison and cattle demonstrated similar distribution of epithelial cell markers villin, vimentin, cytokeratin, E-cadherin and N-cadherin. Interestingly, Ncadherin predominated in the stratified squamous epithelium reflecting its proliferative nature. E. coli O157 strains 86-24 SmR and EDL 933 adhered to RSE cells from both animals with similar diffuse and aggregative patterns, respectively. Conclusion Our observations further support the fact that bison are likely 'wildlife' reservoirs for E. coli O157, harboring these bacteria in their gastrointestinal tract. Our results also extend the utility of the RSE-cell assay, previously developed to elucidate E. coli O157-cattle RAJ interactions, to studies in bison, which are warranted to determine whether these observations in vitro correlate with those occurring in vivo at the RAJ within the bison gastrointestinal tract. [ABSTRACT FROM AUTHOR]

Introduction. Pork meat is a very well regarded food, with high protein content and a good price. It is highly consumed in Cartagena, and this easy commercialization eases that in some cases the meat is not kept and sold under the most strict hygiene conditions. Keeping this meat under inadequate conditions brings infectious agents and an exaggerated number of microorganisms that create a public health problem. Objective. Determine E. coli and identify the O157:H7 serotype in pork meat commercialized in Cartagena's supermarkets during August and September, 2008. Materials and methods. This research work used a quantitative approach with a descriptive cross-sectional type and a MPN (most probable number) technique according to INVIMA's standards, and the Reveal device was used to identify the O157:H7 serotype. 60 samples of pork meat commercialized in 20 supermarkets in Cartagena were taken. 3 samples were taken in each supermarket, corresponding to three different parts of the animal (lean-rib-chop) in order to have a total of 60 samples. Results. E.coli was found in 36 samples, in unacceptable quantities corresponding to a 60%, and the O157:H7 serotype was found in 17 samples, corresponding to a 28%. Conclusion. 60% of the samples contaminated with E. coli and 28% of the samples that turned out to be positive for the O157:H7 serotype, are not considered as safe for human consumption. This demonstrates that there are deficiencies in the microbial quality of the food commercialized in supermarkets located in Cartagena, thus jeopardizing public health. [ABSTRACT FROM AUTHOR]

Introduction: Shiga toxin-producing Escherichia coli (STEC) O157:H7 is associated with intestinal infection in humans and is considered an important cause of food-borne diseases. The aim of the study was to assess the incidence of E. coli O157:H7 in fecal samples of healthy cattle collected in slaughterhouses (n = 160) and from five farms (n = 100)., Methodology: E. coli isolates were detected on MacConkey agar. A total of 236 E. coli isolates were recovered from fecal samples of healthy cattle. We used sorbitol MacConkey medium to detect non-sorbitol fermenting colonies. These bacteria were examined for the presence of O157:H7 antigen by latex agglutination. The isolation of E. coli O157:H7 has been confirmed with PCR amplification of rfbEO157 and fliCH7 specific genes for serogroup O157 and with multiplex PCR of stx1, stx2, eaeA, and ehxA. All isolates were examined for their susceptibility to 21 antibiotics by the disc diffusion method., Results: Of the 236 E. coli isolates, 4.2% (10/236) were positive for STEC O157:H7. Shiga toxin gene (stx2) and ehxA were present in 70% of isolates, stx1 and eae were confirmed in 60% of the isolates. Other virulence factors screened (fimH, sfa/focDE, cdt3, traT, iutA, and hlyA) were present among the 10 isolates. All E. coli O157:H7 isolates were sensitive to amoxicillin/clavulanic acid, cefotaxime, cefepime, aztreonam, colistin, and sulfamethoxazole/trimethoprim. All isolates belong to the phylo-group E., Conclusions: This is the first study of the incidence of E. coli O157:H7 in cattle in Tunisia. Our finding proves the existence of STEC O157:H7 in healthy animals producing food for human consumption which could be a source of food-borne disease., Competing Interests: No Conflict of Interest is declared, (Copyright (c) 2022 Ghassan Tayh, Salma Mariem Boubaker, Rym Ben Khedher, Mounir Jbeli, Faten Ben Chehida, Aymen Mamlouk, Monia Dâaloul-Jedidi, Lilia Messadi.)

Abstract: Our primary objective was to determine the efficacy of a siderophore receptor and porin proteins-based vaccine (VAC) and a Lactobacillus acidophilus-based direct-fed microbial (DFM) against fecal shedding of Escherichia coli O157:H7 in commercial feedlot cattle fed a corn grain-based diet with 25% distiller''s grains. Cattle projected to be on a finishing diet during the summer were randomly allocated into 40 study pens within ten blocks based on allocation dates. Blocks were complete; each of the four pens within a block was randomly assigned one treatment: control, VAC, DFM, or VAC+DFM. The DFM was fed (106 CFU/animal/day of Lactobacillus) throughout the study periods (84–88 days) and cattle were vaccinated at enrollment and again three weeks later. Fresh fecal samples (30/pen) from pen floors were collected weekly for four consecutive weeks (study days 52–77). Two concurrent culture procedures were used to enable estimates of E. coli O157:H7 shedding prevalence and prevalence of high shedders. From 4800 total samples, 1522 (31.7%) were positive for E. coli O157:H7 and 169 (3.5%) were considered high shedders. Pen-level linear mixed models were used for data analyses. There were no significant interactions among treatments and time of sampling. However, vaccinated pens had lower (P <0.01) overall prevalence of E. coli O157:H7 (model-adjusted mean ±SEM=17.4±3.95%) and lower (P <0.01) prevalence of high shedders (0.95±0.26%) than unvaccinated pens (37.0±6.32% and 4.19±0.81%, respectively). There was no evidence of a DFM effect on either measure of E. coli O157:H7 shedding. Results indicate that a two-dose regimen of the vaccine significantly reduces fecal prevalence of E. coli O157:H7 (vaccine efficacy of 53.0%) and prevalence of E. coli O157:H7 high shedders (vaccine efficacy of 77.3%) in commercial feedlot cattle reared in the summer on a finishing diet with 25% distiller''s grains. [Copyright &y& Elsevier]

Shiga toxin-producing Escherichia coli (STEC) causes serious human illness such as hemolytic uremic syndrome (HUS). Argentina has the world's highest rate of this syndrome, which is the leading cause of acute renal failure among children. E. coli O157:H7 is the most common cause of HUS, but a substantial and growing proportion of this illness is caused by infection due to non-O157 strains. Multiple-locus variable-number tandem repeat analysis (MLVA) has become an established technique to subtype STEC. This review will address the use of routine STEC subtyping by MLVA in order to type this group of isolates and to get insight into the genetic diversity of native STEC. With regard to these objectives we modified and adapted two MLVA protocols, one exclusive for O157 and the other, a generic E. coli assay. A total of 202 STEC isolates, from different sources and corresponding to 20 serotypes, have been MLVA genotyped in our laboratory. In our experience, MLVA constitutes a very sensitive tool and enables us to perform an efficient STEC subtyping. The diversity found in many serotypes may be useful for future epidemiological studies of STEC clonality, applied to O157 as well as to non-O157 isolates. [ABSTRACT FROM AUTHOR]