Hazard Identification and Characterization: Criteria for Categorizing Shiga Toxin-Producing Escherichia coli on a Risk Basis†

Prevalence, identification of virulence genes, and antibiotic resistance properties of Shiga-toxin producing Escherichia coli (STEC) strains isolated from ice cream and juice in sales centers

OBJECTIVE

Contaminated food with Shiga-toxin producing Escherichia coli (STEC) can cause diarrhea and severe diseases in consumers. This study aimed to assess the phenotypic and genotypic characteristics of virulence and antibiotic resistance genes in STEC strains isolated from various types of ice cream and fruit juice sold in Isfahan, Iran.

METHODS

From March 2023 to March 2024, 500 samples-including traditional ice cream (100), industrial ice cream (100), frozen ice cream (100), traditional juice (100), and industrial juice (100)-were collected. Samples were analyzed using biochemical and molecular methods for STEC detection. Antibiotic sensitivity was evaluated using the disc diffusion method against 14 antibiotics. Specific primers were used to identify antibiotic resistance and virulence genes.

RESULTS

Among the 500 samples, 52 (10.42%) were E. coli positive, with the highest prevalence found in traditional juice (20%) and traditional ice cream (15%). The pathogenic subtype, particularly enterohemorrhagic E. coli (EHEC), was most common in traditional juice (75% of positive samples) and traditional ice cream (66.66%). High antibiotic resistance rates were observed against ampicillin (86.53%), tetracycline (76.92%), and sulfamethoxazole (73.07%), while the lowest resistance was recorded for imipenem (7.69%). The most frequently detected antibiotic resistance genes were aadA1 (76.92%), tetA (57.69%), and sul1 (55.76%). Key virulence genes included stx1, stx2, and eaeA.

CONCLUSION

These findings emphasize the public health risks associated with STEC contamination in food products and the need for stricter food safety measures and antibiotic stewardship programs. These findings highlight the public health risks of STEC contamination in food products, particularly traditional ice cream and juice. Localized studies are essential to understand specific risks and inform targeted interventions. Strategies such as improved hygiene practices, stringent food safety regulations, and effective antibiotic stewardship programs are critical to mitigating the threat posed by STEC in food products.

Prevalence of Shiga Toxin-Producing Escherichia coli (STEC) and Risk Characterization Based on Virulence Genes in Retail Raw Ground Meat of Beef, Veal, and Lamb in Canada

Shiga toxin-producing Escherichia coli (STEC) are potentially pathogenic E. coli that may cause mild to severe gastrointestinal illnesses. STEC-contaminated foods of animal origin have been the most frequently implicated sources of foodborne outbreaks. A multiyear (2016 to 2021) targeted survey was conducted to investigate the prevalence of STEC in retail ground meats (beef, veal, and lamb). Samples were screened for the presence of Shiga toxin genes (stx) to identify presumptive samples, followed by culture and molecular confirmation of isolates to confirm the presence of stx genes and subsequent characterization by whole-genome-sequencing (WGS) for O serogroup and virulence genes (e.g., stx, eae, aggR). A total of 175 STEC strains were isolated from a total of 148 samples where the presence of viable STEC was confirmed out of 2,398 ground meat samples. This represented 1.2% (7/589 positive, 8 unique strains) of the beef samples, 4.7% (58/1,241 positive, 67 unique strains) of the veal samples, and 14.6% (83/568 positive, 100 unique strains) of the lamb samples. The intimin virulence gene, eae, was identified in the STEC strains of veal origin (9/67, 13.4%) only and were classified as belonging to risk level 1 (1/67), level 3 (2/67), and level 4 (6/67) according to the FAO/WHO risk categories. Risk level 2 STEC strains were of beef (2/8, 25.0%), veal (8/67, 11.9%), and lamb (1/100, 1.0%) origin. The majority of the STEC strains, 75.0% (6/8) of the beef, 67.2% (45/67) of the veal, and 94.0% (94/100) of the lamb STEC strains were classified as risk level 5 (lowest level) of the FAO/WHO risk categories. This study's findings indicate that the current food safety control measures implemented for ground meats in Canada are effective at maintaining an acceptable level of possible contamination with STEC strains associated with severe clinical outcomes. Continued application of effective control measures and safe food handling practices by consumers will minimize the potential risk of foodborne infections from raw ground meats.

Prevalence of Shiga toxin-producing Escherichia coli, Salmonella, and Campylobacter species among diarrheal patients from three major hospitals in Ethiopia

Diarrheal illness remains a major global health challenge, causing millions of deaths annually. Non-typhoidal Salmonella (NTS), Shiga toxin-producing Escherichia coli (STEC), and Campylobacter species (CAMPY) significantly contribute to this burden. Given the limited information on these pathogens in Ethiopia, this study aimed to estimate their prevalence among diarrhea patients in Ethiopia and identify risk factors for infection. A cross-sectional study was conducted from October 2021 to November 2022 in three hospitals in Ethiopia (Addis Ababa, Gondar, and Harar). Sociodemographic characteristics, clinical signs and symptoms were collected from study participants using a structured questionnaire. Stool samples were tested for NTS, STEC, and CAMPY using standardized methods. The prevalence of targeted pathogens was estimated overall and by study sites. Univariable and multivariable logistic regression were used to identify associated factors. A total of 2,331 patients were enrolled. The overall prevalence of NTS, STEC (stx only), STEC (stx + eae), and CAMPY was 1.29% (95%CI: 0.91, 1.84), 12.56% (95%CI: 11.29, 13.98), 3.43% (95%CI: 2.77, 4.25), and 4.46% (95%CI: 4.61, 8.00), respectively. Harar had the highest prevalence of all the pathogens compared to Addis Ababa and Gondar. Odds of NTS in Harar were over 10 (AOR: 10.43: 95%CI: 2.95, 69.20) and 3.5 times (AOR: 3.57: 95%CI: 1.50, 9.90) higher than that in Addis Ababa and Gondar, respectively. Odds of STEC (stx only) in the dry (AOR: 1.97: 95%CI: 1.37, 2.90) and long rainy (AOR: 1.80: 95%CI: 1.20, 2.69) seasons were nearly twice the odds in the short rainy season. Odds of CAMPY infection decreased by 3.29% (AOR: 0.97: 95%CI: 0.95, 0.98) with every one-year increase in age. Moreover, the odds of CAMPY infection for rural residents (AOR: 1.93, 95%CI: 1.15, 3.19) were nearly twice that of urban residents. This is the first study to estimate the prevalence of NTS, STEC, and CAMPY simultaneously across all age groups and diverse regions in Ethiopia, revealing significant variations. Results can be used to understand the burden of disease, inform clinical management and risk mitigation strategies to reduce illness in Ethiopia.

A novel multiplex and glycoprotein-based immunochromatographic serologic IgM test for the rapid diagnosis of Escherichia coli O157 and O145 causing bloody diarrhea and hemolytic uremic syndrome

Shiga toxin-producing Escherichia coli (STEC) are the main etiological agents of hemolytic uremic syndrome (HUS). Good clinical management of STEC infections and HUS depends on early, rapid, and accurate diagnosis. Here, we have developed and evaluated the first multiplex and glycoprotein-based immunochromatographic test for the detection of IgM antibodies against the O-polysaccharide of the lipopolysaccharide of E. coli O157 and O145 in human serum samples. A retrospective study was carried out resulting in a diagnostic sensitivity of the E. coli O157/O145 LFIA (lateral flow immunoassay) of 97.1% and 98.9% for O157 and O145, respectively, and 97.9% for both serogroups. The diagnostic specificity was 98.7% for O157 and O145, and the overall specificity 97.4%. In samples obtained before 3 days after the onset of diarrhea, the detection percentage was 83%, increasing to 100% from 3 days onward. Finally, the association of bloody diarrhea (BD) or HUS cases to an STEC infection increased from 22.8% to 77.2% when stool culture and stx/Stx detection were combined with serology by LFIA. Our results demonstrate that the E. coli O157/O145 LFIA is a highly accurate and serospecific test for the early and rapid diagnosis of E. coli O157 and O145 infections in BD or HUS cases. This test allows the detection of specific IgM antibodies very early in the course of the infection, making it an ideal diagnostic tool to be implemented in pediatric emergencies and, thus, avoid delays in the application of the correct supportive or specific treatment and prevent complications associated with HUS.

Emerging of Shiga toxin-producing Escherichia coli O177:H11 and O177:H25 from cattle at slaughter in Italy

Shiga toxin-producing Escherichia coli (STEC) are zoonotic pathogens frequently carried by cattle, responsible in humans of mild to bloody diarrhoea, haemolytic uraemic syndrome (HUS) and even death. In 2023-2024, a study on STEC contamination of hide and carcasses of dairy cattle at slaughter was planned in Emilia-Romagna region (northern Italy). When the study was still in progress and 60 animals were sampled, the detection of STEC O177 isolates reached high rates and gained our attention. A total of five O177 STEC strains were detected, namely four from three carcasses (5.0 %) and one from a hide sample (1.7 %). The isolates were typed by WGS as following: 1) STEC O177:H11 sequence type (ST) 765 (stx2a+, eae+), detected from one carcass; 2) STEC O177:H25 ST659 (stx2c+, eae+) detected from three carcasses and one hide sample. One carcass was contaminated by both STEC serotypes. The isolates carried other virulence determinants often found in STEC strains associated with HUS, namely the exha, astA and espP genes, together with genes for adhesion to the epithelial cells of the gut (lpfA, fdeC, fimH) and non-Locus for Enterocyte Effacement (LEE) effector protein genes (nleA, nleB). The STEC O177:H11 isolate harboured antimicrobial resistance (AMR) genes to β-lactams (blaTEM-1A), aminoglycosides (aadA1, aph(3″)-Ib, aph(6)-Id), trimethoprim (dfrA1), sulphonamides (sul1, sul2), tetracyclines (tetA), (tetB), streptothricin (sat2), and quaternary ammonium compounds (qacEdelta1). On the contrary, the STEC O177:H25 isolates carried no AMR genes. Persistent carriage of STEC O177:H25 ST659 (stx2c+, eae+) at farm level was assessed by testing animals of the same herd sent to slaughter. Interestingly, the colonies of STEC O177:H11 and STEC O177:H25 had different morphology on CHROMagar™ STEC plates, being mauve and colourless, respectively. Since mauve is the colour STEC colonies commonly have on the CHROMagar™ STEC medium, our findings can help microbiologists in the selection of uncommon serotypes. To the best of our knowledge, this is the first detection of STEC O177 from carcasses and hides of dairy cattle at slaughter. Noteworthy, the STEC-positive hide was classified as "very dirty" thus stressing the need of clean animals entering the slaughter chain, as required by Regulation (EC) No 853/2004. Since STEC O177 has been responsible of HUS in Europe, our data could add information on the source of uncommon serogroups in human infections.

Evidence for Horizontal Transmission and Recirculation of Shiga Toxin-Producing Escherichia coli in the Beef Production Chain in South Africa Using Whole Genome Sequencing

We used whole genome sequencing (WGS) as an epidemiologic surveillance tool to elucidate the transmission dynamics of Shiga toxin-producing Escherichia coli (STEC) strains along the beef production chain in South Africa. Isolates were obtained from a cattle farm, abattoirs and retail outlets. Isolates were analysed using WGS on a MiSeq platform (Illumina, San Diego, CA, USA) and phylogenetic analysis was carried out. Of the 85 isolates, 39% (33) carried the stx gene and 61% (52) had lost the stx gene. The prevalence of stx subtypes was as follows; stx1a 55% (18/33), stx1b 52% (17/33), stx2a 55% (18/33), stx2b 27% (9/33), stx2dB 30% (10/33) and stx2d1A 15% (5/33). Thirty-five different serogenotypes were detected, of which 65% (56) were flagellar H-antigens and 34% (29) were both O-antigens and flagellar H-antigens. We identified 50 different sequence types (STs), and only nine of the isolates were assigned to three different clonal complexes. Core genome phylogenetic analysis revealed genetic relatedness, and isolates clustered mainly according to their STs and serogenotypes regardless of stx subtypes. This study provides evidence of horizontal transmission and recirculation of STEC strains in Gauteng province and demonstrates that every stage of the beef production chain plays a significant role in STEC entry into the food chain.

Shiga Toxin-Producing Escherichia coli Isolated from Wild Ruminants in Liguria, North-West Italy

Wildlife may represent an important source of infectious diseases for humans and other wild and domestic animals. Wild ruminants can harbour and transmit Shiga toxin-producing Escherichia coli (STEC) to humans, and some strains even carry important antimicrobial resistance. In this study, 289 livers of wild roe deer, fallow deer, red deer and chamois collected in Liguria, north-west Italy, from 2019 to 2023 were analysed. Overall, 44 STEC strains were isolated from 28 samples. The characterisation of serogroups showed the presence of O104, O113, O145 and O146 serogroups, although for 28 colonies, the serogroup could not be determined. The most prevalent Shiga toxin gene in isolated strains was Stx2, and more specifically the subtype Stx2b. The other retrieved subtypes were Stx1a, Stx1c, Stx1d and Stx2g. The isolated strains generally proved to be susceptible to the tested antimicrobials. However, multi-drug resistances against highly critical antimicrobials were found in one strain isolated from a roe deer. This study highlights the importance of wildlife monitoring in the context of a "One Health" approach.

Characterization of Shiga Toxin-producing Escherichia coli Isolated from Cattle Around Ulaanbaatar City, Mongolia

Shiga toxin-producing Escherichia coli (STEC) are associated with severe infections including hemorrhagic colitis and hemolytic uremic syndrome in humans. Ruminants are known as reservoirs of STEC; however, no data are available on STEC in ruminants in Mongolia, where more than 5 million cattle and 25 million sheep are raised. To disclose the existence and characteristics of STEC in Mongolia, in this study, we isolated and characterized STEC from cattle in Mongolia. We collected 350 rectal swabs of cattle from 30 farms near Ulaanbaatar city and isolated 45 STEC from 21 farms. Rectal swabs were precultured with modified Escherichia coli broth and then inoculated to Cefixime-Tellurite Sorbitol MacConkey agar plate and/or CHROMagar STEC agar plate for the isolation of STEC. The isolation ratios in each farm were from 0% to 40%. Multiplex PCR for the estimation of O- and H-serotypes identified 12 O-genotypes (Og-types) and 11 H-genotypes (Hg-types) from 45 isolates; however, Og-types of 19 isolates could not be determined. Stx gene subtyping by PCR identified 2 stx1 subtypes (1a and 1c) and 4 stx2 subtypes (2a, 2c, 2d, and 2g). Forty-five isolates were divided into 21 different groups based on the Og- and Hg-types, stx gene subtypes and the existence of virulence factors, ehxA, eae, and saa, which includes several major serotypes associated with human illness such as O26:H11 and O157:H7. The most dominant isolate, OgUT:H19 [stx1a (+), stx2a (+), ehxA (+) and saa (+)], was isolated from eight farms. This is the first report on the characterization of STEC in cattle in Mongolia, and the results suggest the importance of further monitoring of STEC contamination in the food chains as well as STEC infection in humans.

Shiga Toxin‒Producing Escherichia coli Diagnoses from Health Practitioners, Queensland, Australia

In Queensland, Australia, 31 of 96 Shiga toxin‒producing Escherichia coli cases during 2020-2022 were reported by a specialty pathology laboratory servicing alternative health practitioners. Those new cases were more likely to be asymptomatic or paucisymptomatic, prompting a review of the standard public health response.

RNA-Seq analysis of long non-coding RNA in human intestinal epithelial cells infected by Shiga toxin-producing Escherichia coli

BACKGROUND

The Shiga toxin-producing Escherichia coli (STEC) infects animals and induces acute intestinal inflammation. Long non-coding RNAs (lncRNAs) are known to play crucial roles in modulating inflammation response. However, it is not clear whether lncRNAs are involved in STEC-induced inflammation.

METHODS AND RESULTS

To understand the association of lncRNAs with STEC infection, we used RNA-seq technology to analyze the profiles of lncRNAs in Mock-infected and STEC-infected human intestinal epithelial cells (HIECs). We detected a total of 702 lncRNAs differentially expressed by STEC infection. 583 differentially expressed lncRNAs acted as competitive microRNAs (miRNAs) binding elements in regulating the gene expression involved in TNF signaling pathway, IL-17 signaling pathway, PI3K-Akt signaling pathway, and apoptosis pathways. We analyzed 3 targeted genes, TRADD, TRAF1 and TGFB2, which were differentially regulated by mRNA-miRNA-lncRNA interaction network, potentially involved in the inflammatory and apoptotic response to STEC infection. Functional analysis of up/downstream genes associated with differentially expressed lncRNAs revealed their role in adheres junction and endocytosis. We also used the qRT-PCR technique to validate 8 randomly selected differentially expressed lncRNAs and mRNAs in STEC-infected HIECs.

CONCLUSION

Our results, for the first time, revealed differentially expressed lncRNAs induced by STEC infection of HIECs. The results will help investigate the molecular mechanisms for the inflammatory responses induced by STEC.

Pathogenicity assessment of Shiga toxin-producing Escherichia coli strains isolated from wild birds in a major agricultural region in California

Shiga toxin-producing Escherichia coli (STEC) consists of diverse strains differing in genetic make-up and virulence potential. To better understand the pathogenicity potential of STEC carried by the wildlife, three STEC and one E. coli strains isolated from wild birds near a major agricultural region in California were selected for comparative pathogenomic analyses. Three American crow (Corvus brachyrhynchos) strains, RM9088, RM9513, and RM10410, belonging to phylogroup A with serotypes O109:H48, O9:H30, and O113:H4, respectively, and a red-winged blackbird (Agelaius phoeniceus) strain RM14516 in phylogroup D with serotype O17:H18, were examined. Shiga toxin genes were identified in RM9088 (stx1a), RM10410 (stx1a + stx2d), and RM14516 (stx2a). Unlike STEC O157:H7 strain EDL933, none of the avian STEC strains harbored the pathogenicity islands OI-122, OI-57, and the locus of enterocyte effacement, therefore the type III secretion system biogenesis genes and related effector genes were absent in the three avian STEC genomes. Interestingly, all avian STEC strains exhibited greater (RM9088 and RM14516) or comparable (RM10410) cytotoxicity levels compared with EDL933. Comparative pathogenomic analyses revealed that RM9088 harbored numerous genes encoding toxins, toxins delivery systems, and adherence factors, including heat-labile enterotoxin, serine protease autotransporter toxin Pic, type VI secretion systems, protein adhesin Paa, fimbrial adhesin K88, and colonization factor antigen I. RM9088 also harbored a 36-Kb high pathogenicity island, which is related to iron acquisition and pathogenicity in Yersinia spp. Strain RM14516 carried an acid fitness island like the one in EDL933, containing a nine gene cluster involved in iron acquisition. Genes encoding extracellular serine protease EspP, subtilase cytotoxin, F1C fimbriae, and inverse autotransporter adhesin IatC were only detected in RM14516, and genes encoding serine protease autotransporter EspI and P fimbriae were only identified in RM10410. Although all curli genes were present in avian STEC strains, production of curli fimbriae was only detected for RM9088 and RM14516. Consistently, strong, moderate, and little biofilms were observed for RM9088, RM14516, and RM10410, respectively. Our study revealed novel combinations of virulence factors in two avian strains, which exhibited high level of cytotoxicity and strong biofilm formation. Comparative pathogenomics is powerful in assessing pathogenicity and health risk of STEC strains.

The Fatal Role of Enterohaemorrhagic Escherichia coli Shiga Toxin-associated Extracellular Vesicles in Host Cells

Enterohemorrhagic Escherichia coli (EHEC) is a specific subset of Shiga toxin-producing Escherichia coli (STEC) strains that are characterized by their ability to cause bloody diarrhea (hemorrhagic colitis) and potentially life-threatening, extraintestinal complications such as hemolytic uremic syndrome (HUS), which is associated with acute renal failure., contributing to severe clinical outcomes. The Shiga toxins (Stxs), produced by EHEC, are primary virulence factors. These potent cytotoxins are composed of one enzymatically active A subunit (StxA) and five receptor-binding B subunits (StxB). Although the toxins are primarily associated with cytotoxic effects, they also elicit other pathogenic consequences due to their induction of a number of biological processes, including apoptosis through ER-stress, pro-inflammatory responses, autophagy, and post-translational modification (PTM). Moreover, several studies have reported the association between Stxs and extracellular vesicles (EVs), including microvesicles and exosomes, demonstrating that Stx-containing EVs secreted by intoxicated macrophages are taken up by recipient cells, such as toxin-sensitive renal proximal tubular epithelial cells. This mechanism likely contributes to the spreading of Stxs within the host, and may exacerbate gastrointestinal illnesses and kidney dysfunction. In this review, we summarize recent findings relating to the host responses, in different types of cells in vitro and in animal models, mediated by Stxs-containing exosomes. Due to their unique properties, EVs have been explored as therapeutic agents, drug delivery systems, and diagnostic tools. Thus, potential therapeutic applications of EVs in EHEC Stxs-mediated pathogenesis are also briefly reviewed.

Phenotypic and genotypic characterization of pathogenic Escherichia coli identified in resistance mapping of β-lactam drug-resistant isolates from seafood along Tuticorin coast

The ubiquity of pathogenic E. coli isolate possessing antimicrobial resistance was investigated in seafood samples procured from major seafood supply chain markets established for export and domestic consumption along Tuticorin coast. Out of 63 seafood samples examined, 29 (46%) were found to be contaminated by pathogenic E. coli harbouring one or more genes of virulent potential. Based on virulome profiling, 9.55% of isolates belonged to enterotoxigenic E. coli (ETEC), 8.08% to enteroaggregative E. coli (EAEC), 7.35% to enterohemorrhagic E. coli (EHEC), 2.20% to enteropathogenic E. coli (EPEC), and 2.20% to uropathogenic E. coli (UPEC). All the 34 virulome positive and haemolytic pathogenic E. coli have been serogrouped as O119, O76, O18, O134, O149, O120, O114, O25, O55, O127, O6, O78, O83, O17 and clinically significant O111, O121, O84, O26, O103, and O104 (non-O157 STEC) serotypes in this study. Multi-drug resistance (MDR) (≥ 3 antibiotic classes/sub-classes) was exhibited in 38.23% of the pathogenic E. coli, and 17.64% were extensive drug resistant (XDR). Extended spectrum of β-lactamase (ESBL) genotypes were confirmed in 32.35% isolates and 20.63% isolates harboured ampC gene. One sample (Penaeus semisulcatus) collected from landing centre (L1) harboured all ESBL genotypes bla_CTX-M, bla_SHV, bla_TEM, and ampC genes. Hierarchical clustering of isolates revealed the separation of ESBL isolates into three clusters and non-ESBL isolates into three clusters based on phenotypic and genotypic variations. Based on dendrogram analysis on antibiotic efficacy pattern, carbapenems and β-lactam inhibitor drugs are the best available treatment for ESBL and non-ESBL infections. This study emphasizes the significance of comprehensive surveillance of pathogenic E. coli serogroups that pose serious threat to public health and compliance of AMR antimicrobial resistant genes in seafood that hinder seafood supply chain.

Prevalence and characterization of the seven major serotypes of Shiga toxin-producing Escherichia coli (STEC) in veal calves slaughtered in France

Shiga toxin (Stx)-producing Escherichia coli (STEC) belonging to the "top 7″ serotypes (i.e. O157:H7, O26:H11, O45:H2, O103:H2, O111:H8, O121:H19 and O145:H28) are considered as the main pathogenic enterohemorrhagic E. coli (EHEC). As ruminants, including calves, are a reservoir of pathogenic STEC, we investigated the prevalence, major virulence genes and genetic relatedness of top7 STEC in veal calves slaughtered in France, through the analysis of 500 fecal samples collected over one year. Thirty top7 STEC isolates were recovered from 28 calves. The two serotypes O103:H2 and O26:H11 accounted for 73% of STEC strains, followed by O145:H28 and O157:H7. STEC super-shedding levels were identified for two calves carrying STEC O103:H2 and O157:H7, respectively. Thirty-nine atypical enteropathogenic E. coli (aEPEC) were also recovered from calves. Overall, a prevalence of 5.6% top7 STEC-positive calves was found, thus higher than that previously determined for the French slaughtered adult cattle (1.8%), confirming the impact of animals age on STEC carriage. Most top7 STEC strains carried the stx1a subtype suggesting a low pathogenicity for humans. Seasonal variation in STEC carriage was also observed, with two peaks of higher prevalence during spring and fall. Genetic similarity of top7 STEC isolates was found for calves originating from the same fattening facilities, reflecting STEC circulation between animals kept in groups. This study indicates that veal calves grown for meat production are at higher risk of shedding top7 STEC compared to adult cattle. They thus represent ideal targets for the implementation of farm interventions aimed at reducing STEC burden in cattle and the food chain.

Dual-Gene Isothermal Amplification Coupled with Lateral Flow Strip for On-Site Accurate Detection of E. coli O157:H7 in Food Samples

On-site field detection of E. coli O157:H7 in food samples is of utmost importance, since it causes a series of foodborne diseases due to infections-associated ready-to-eat foods. Due to the instrument-free nature, recombinase polymerase amplification (RPA) coupled with lateral flow assay (LFA) is well-suited for such goal. However, the high genomic similarity of different E. coli serotypes adds difficulty to accurate differentiation of E. coli O157:H7 from others. Dual-gene analysis could significantly improve the serotype selectivity, but will further aggravate the RPA artifacts. To address such issue, here we proposed a protocol of dual-gene RPA-LFA, in which the target amplicons were selectively recognized by peptide nucleic acid (PNA) and T7 exonuclease (TeaPNA), thus eliminating false-positives in LFA readout. Adapting rfbE_O157 and fliC_H7 genes as the targets, dual-gene RPA-TeaPNA-LFA was demonstrated to be selective for E. coli O157:H7 over other E. coli serotypes and common foodborne bacteria. The minimum detection concentration was 10 copies/μL for the genomic DNA (∼300 cfu/mL E. coli O157:H7), and 0.24 cfu/mL E. coli O157:H7 in food samples after 5 h bacterial preculture. For lettuce samples contaminated with E. coli O157:H7 (single-blind), the sensitivity and specificity of the proposed method were 85% and 100%, respectively. Using DNA releaser for fast genomic DNA extraction, the assay time could be reduced to ∼1 h, which is appealing for on-site food monitoring.

Shiga Toxin-Producing Escherichia coli in Faecal Samples from Wild Ruminants

Wildlife can harbour Shiga toxin-producing Escherichia coli (STEC). In the present study, STEC in faecal samples from red deer (n = 106) and roe deer (n = 95) were characterised. All isolates were non-O157 strains. In red deer, STEC were detected in 17.9% (n = 19) of the isolates, and the eae/stx_2b virulence profile was detected in two isolates (10.5%). One STEC strain harboured stx_1a (5.3%) and eighteen STEC strains harboured stx₂ (94.7%). The most prevalent stx₂ subtypes were stx_2b (n = 12; 66.7%), stx_2a (n = 3; 16.7%), and stx_2g (n = 2; 11.1%). One isolate could not be subtyped (NS) with the applied primers (5.6%). The most widely identified serotypes were O146:H28 (n = 4; 21%), O146:HNM (n = 2; 10.5%), O103:H7 (n = 1; 5.3%), O103:H21 (n = 1; 5.3%), and O45:HNM (n = 1; 5.3%). In roe deer, STEC were detected in 16.8% (n = 16) of the isolates, and the eae/stx_2b virulence profile was detected in one isolate (6.3%). Two STEC strains harboured stx_1a (12.5%), one strain harboured stx_1NS/stx_2b (6.3%), and thirteen strains harboured stx₂ (81.3%). The most common subtypes were stx_2b (n = 8; 61.5%), stx_2g (n = 2; 15.4%), non-typeable subtypes (NS) (n = 2; 15.4%), and stx_2a (n = 1; 7.7%). Serotype O146:H28 (n = 5; 31.3%) was identified. The study demonstrated that the zoonotic potential of STEC strains isolated from wildlife faeces should be monitored in the context of the 'One Health' approach which links human health with animal and environmental health.

Serotype-dependent adhesion of Shiga toxin-producing Escherichia coli to bovine milk fat globule membrane proteins

Shiga toxin-producing Escherichia coli (STEC) are food-borne pathogens that can cause severe symptoms for humans. Raw milk products are often incriminated as vehicule for human STEC infection. However, raw milk naturally contains molecules, such as the milk fat globule membrane and associated proteins, that could inhibit pathogen adhesion by acting as mimetic ligands. This study aimed to: (i) evaluate the capability of STEC cells to adhere to bovine milk fat globule membrane proteins (MFGMPs), (ii) highlight STEC surface proteins associated with adhesion and (iii) evaluate the variation between different STEC serotypes. We evaluated the physicochemical interactions between STEC and milk fat globules (MFGs) by analyzing hydrophobic properties and measuring the ζ-potential. We used a plate adhesion assay to assess adhesion between MFGMPs and 15 Escherichia coli strains belonging to three key serotypes (O157:H7, O26:H11, and O103:H2). A relative quantitative proteomic approach was conducted by mass spectrometry to identify STEC surface proteins that may be involved in STEC-MFG adhesion. The majority of E. coli strains showed a hydrophilic profile. The ζ-potential values were between -3.7 and - 2.9 mV for the strains and between -12.2 ± 0.14 mV for MFGs. Our results suggest that non-specific interactions are not strongly involved in STEC-MFG association and that molecular bonds could form between STEC and MFGs. Plate adhesion assays showed a weak adhesion of O157:H7 E. coli strains to MFGMPs. In contrast, O26:H11 and O103:H2 serotypes attached more to MFGMPs. Relative quantitative proteomic analysis showed that the O26:H11 str. 21,765 differentially expressed five outer membrane-associated proteins or lipoproteins compared with the O157:H7 str. EDL933. This analysis also found strain-specific differentially expressed proteins, including four O26:H11 str. 21,765-specific proteins/lipoproteins and eight O103:H2 str. PMK5-specific proteins. For the first time, we demonstrated STEC adhesion to MFGMPs and discovered a serotype effect. Several outer membrane proteins-OmpC and homologous proteins, intimin, Type 1 Fimbriae, and AIDA-I-that may be involved in STEC-MFG adhesion were highlighted. More research on STEC's ability to adhere to MFGMs in diverse biological environments, such as raw milk cheeses and the human gastrointestinal tract, is needed to confirm the anti-adhesion properties of the STEC-MFG complex.

Prevalence and Implications of Shiga Toxin-Producing E. coli in Farm and Wild Ruminants

Shiga-toxin-producing Escherichia coli (STEC) is a food-borne pathogen that causes human gastrointestinal infections across the globe, leading to kidney failure or even death in severe cases. E. coli are commensal members of humans and animals' (cattle, bison, and pigs) guts, however, may acquire Shiga-toxin-encoded phages. This acquisition or colonization by STEC may lead to dysbiosis in the intestinal microbial community of the host. Wildlife and livestock animals can be asymptomatically colonized by STEC, leading to pathogen shedding and transmission. Furthermore, there has been a steady uptick in new STEC variants representing various serotypes. These, along with hybrids of other pathogenic E. coli (UPEC and ExPEC), are of serious concern, especially when they possess enhanced antimicrobial resistance, biofilm formation, etc. Recent studies have reported these in the livestock and food industry with minimal focus on wildlife. Disturbed natural habitats and changing climates are increasingly creating wildlife reservoirs of these pathogens, leading to a rise in zoonotic infections. Therefore, this review comprehensively surveyed studies on STEC prevalence in livestock and wildlife hosts. We further present important microbial and environmental factors contributing to STEC spread as well as infections. Finally, we delve into potential strategies for limiting STEC shedding and transmission.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Bacterial Distribution and Community Structure in Beef Cattle Liver and Bile at Slaughter

ABSTRACT

In this study, the distribution of hygienic indicator bacteria in cattle livers and bile was examined at slaughterhouses. One hundred twenty-seven cattle livers with gallbladders were carefully eviscerated from carcasses at 10 slaughterhouses. Microbiological examination revealed that nine bile samples (7.1% prevalence) and 19 liver parenchyma samples (15.0% prevalence) were positive for Enterobacteriaceae (EB) with means ± standard deviations of 3.68 ± 4.63 log CFU/mL and 1.59 ± 2.47 log CFU/g, respectively; thus, bacterial contamination was apparent even at the postevisceration stage. Subsequently, 70 cattle livers were obtained at the postprocessing and storage stage from 7 of the 10 slaughterhouses. Microbiological analysis revealed significantly higher levels of EB in the liver parenchyma (3.00 ± 3.89 log CFU/g, P = 0.011) than those at the postevisceration stage, suggesting that bacterial dissemination and/or replication occurred in the liver parenchyma during processing and storage. According to 16S rRNA ion semiconductor sequencing analysis of representative samples from 12 cattle, Proteobacteria, Firmicutes, and Actinobacteria were dominant in both the parenchyma and bile in which EB and Escherichia coli were predominant among livers with higher EB levels. These results suggest that bile plays a role as a vehicle for bacterial transmission to the liver parenchyma. This study is the first to evaluate bacterial distribution and community structure in the liver and biliary microecosystem of cattle at slaughter. Our data support the use of EB testing of bile to screen cattle livers contaminated with high levels of fecal indicator bacteria.

HIGHLIGHTS

Shiga Toxin-Producing Escherichia coli and Milk Fat Globules

Shiga toxin-producing Escherichia coli (STEC) are zoonotic Gram-negative bacteria. While raw milk cheese consumption is healthful, contamination with pathogens such as STEC can occur due to poor hygiene practices at the farm level. STEC infections cause mild to serious symptoms in humans. The raw milk cheese-making process concentrates certain milk macromolecules such as proteins and milk fat globules (MFGs), allowing the intrinsic beneficial and pathogenic microflora to continue to thrive. MFGs are surrounded by a biological membrane, the milk fat globule membrane (MFGM), which has a globally positive health effect, including inhibition of pathogen adhesion. In this review, we provide an update on the adhesion between STEC and raw MFGs and highlight the consequences of this interaction in terms of food safety, pathogen detection, and therapeutic development.

Improved Genomic Identification, Clustering, and Serotyping of Shiga Toxin-Producing Escherichia coli Using Cluster/Serotype-Specific Gene Markers

Shiga toxin-producing Escherichia coli (STEC) have more than 470 serotypes. The well-known STEC O157:H7 serotype is a leading cause of STEC infections in humans. However, the incidence of non-O157:H7 STEC serotypes associated with foodborne outbreaks and human infections has increased in recent years. Current detection and serotyping assays are focusing on O157 and top six (“Big six”) non-O157 STEC serogroups. In this study, we performed phylogenetic analysis of nearly 41,000 publicly available STEC genomes representing 460 different STEC serotypes and identified 19 major and 229 minor STEC clusters. STEC cluster-specific gene markers were then identified through comparative genomic analysis. We further identified serotype-specific gene markers for the top 10 most frequent non-O157:H7 STEC serotypes. The cluster or serotype specific gene markers had 99.54% accuracy and more than 97.25% specificity when tested using 38,534 STEC and 14,216 non-STEC E. coli genomes, respectively. In addition, we developed a freely available in silico serotyping pipeline named STECFinder that combined these robust gene markers with established E. coli serotype specific O and H antigen genes and stx genes for accurate identification, cluster determination and serotyping of STEC. STECFinder can assign 99.85% and 99.83% of 38,534 STEC isolates to STEC clusters using assembled genomes and Illumina reads respectively and can simultaneously predict stx subtypes and STEC serotypes. Using shotgun metagenomic sequencing reads of STEC spiked food samples from a published study, we demonstrated that STECFinder can detect the spiked STEC serotypes, accurately. The cluster/serotype-specific gene markers could also be adapted for culture independent typing, facilitating rapid STEC typing. STECFinder is available as an installable package (https://github.com/LanLab/STECFinder) and will be useful for in silico STEC cluster identification and serotyping using genome data.

Shiga toxin-producing Escherichia coli diagnosed by Stx PCR: assessing the public health risk of non-O157 strains

BACKGROUND

The implementation by diagnostic laboratories in England of polymerase chain reaction (PCR) to screen faecal specimens for Shiga toxin-producing Escherichia coli (STEC) has resulted in a significant increase in notifications mainly due to non-O157 strains. The purpose of this study was to develop an approach to public health risk assessment that prioritizes follow-up to cases caused by haemolytic uraemic syndrome (HUS) associated E. coli (HUSEC) strains and minimizes unnecessary actions.

METHODS

Epidemiological and microbiological data were prospectively collected from 1 November 2013 to 31 March 2017 and used to compare three risk assessment approaches.

RESULTS

A history of HUS/bloody diarrhoea/age under 6 years and faecal specimens positive for stx-predicted HUSEC with a diagnostic accuracy of 84% (95% CI; 81-88%). STEC isolated by Gastrointestinal Bacteria Reference Unit (GBRU) and stx2 and eae positive predicted HUSEC with a diagnostic accuracy of 99% (95% CI; 98-100%). Risk assessment combining these two tests predicts the most efficient use of resources, predicting that 18% (97/552) of cases would be eligible for follow-up at some stage, 16% (86/552) following local stx PCR results, 1% (7/552) following GBRU results of stx2 and eae status and 0.7% (4/552) following whole-genome sequencing. Follow-up could be stopped in 78% (76/97) of these cases, 97% (74/76) following second stage risk assessment.

CONCLUSIONS

This three-stage risk assessment approach prioritizes follow-up to HUSEC and minimizes unnecessary public health actions. We developed it into the algorithm for public health actions included in the updated PHE Guidance for management of STEC published in August 2018.

Diversity of Non-O157 Shiga Toxin-Producing Escherichia coli Isolated from Cattle from Central and Southern Chile

Simple Summary

Cattle are the main reservoir of Shiga toxin-producing E. coli (STEC), foodborne pathogens that cause severe disease and outbreaks. However, not all STEC cause human illnesses or have the same virulence potential. Characterizing strains isolated worldwide allows insights into how strains spread and which isolates have a more significant risk potential. This study described STEC isolation rates from cattle in Chile and characterized 30 isolates. We obtained 93 STEC isolates from 56/446 (12.6%) fecal cattle samples. Then, 30 non-O157 STEC isolates were selected for complete characterization; we found isolates of 16 different sequence types and 17 serotypes. One isolate was resistant to tetracycline and carried resistance genes against the drug. Surveyed virulence genes (n = 31) were present from 13% to 100% of isolates, and one isolate carried 26/31 virulence genes. Most isolates (90%; 27/30) carried the stx2 gene, which is frequently linked to strains causing severe disease. A phylogenetic reconstruction demonstrated that isolates clustered based on serotypes, independent of their geographical origin (Central or Southern Chile). These results indicate that cattle in Chile carry a wide diversity of STEC potentially pathogenic for humans based on the presence of virulence genes.

Abstract

Cattle are the main reservoir of Shiga toxin-producing Escherichia coli (STEC), one of the world’s most important foodborne pathogens. The pathogen causes severe human diseases and outbreaks. This study aimed to identify and characterize non-O157 STEC isolated from cattle feces from central and southern Chile. We analyzed 446 cattle fecal samples and isolated non-O157 STEC from 12.6% (56/446); a total of 93 different isolates were recovered. Most isolates displayed β-glucuronidase activity (96.8%; 90/93) and fermented sorbitol (86.0%; 80/93), whereas only 39.8% (37/93) were resistant to tellurite. A subgroup of 30 representative non-O157 STEC isolates was selected for whole-genome sequencing and bioinformatics analysis. In silico analysis showed that they grouped into 16 different sequence types and 17 serotypes; the serotypes most frequently identified were O116:H21 and O168:H8 (13% each). A single isolate of serotype O26:H11 was recovered. One isolate was resistant to tetracycline and carried resistance genes tet(A) and tet(R); no other isolate displayed antimicrobial resistance or carried antimicrobial resistance genes. The intimin gene (eae) was identified in 13.3% (4/30) of the genomes and 90% (27/30) carried the stx2 gene. A phylogenetic reconstruction demonstrated that the isolates clustered based on serotypes, independent of geographical origin. These results indicate that cattle in Chile carry a wide diversity of STEC potentially pathogenic for humans based on the presence of critical virulence genes.

Escherichia coli Shiga Toxins and Gut Microbiota Interactions

Escherichia coli (EHEC) and Shigella dysenteriae serotype 1 are enterohemorrhagic bacteria that induce hemorrhagic colitis. This, in turn, may result in potentially lethal complications, such as hemolytic uremic syndrome (HUS), which is characterized by thrombocytopenia, acute renal failure, and neurological abnormalities. Both species of bacteria produce Shiga toxins (Stxs), a phage-encoded exotoxin inhibiting protein synthesis in host cells that are primarily responsible for bacterial virulence. Although most studies have focused on the pathogenic roles of Stxs as harmful substances capable of inducing cell death and as proinflammatory factors that sensitize the host target organs to damage, less is known about the interface between the commensalism of bacterial communities and the pathogenicity of the toxins. The gut contains more species of bacteria than any other organ, providing pathogenic bacteria that colonize the gut with a greater number of opportunities to encounter other bacterial species. Notably, the presence in the intestines of pathogenic EHEC producing Stxs associated with severe illness may have compounding effects on the diversity of the indigenous bacteria and bacterial communities in the gut. The present review focuses on studies describing the roles of Stxs in the complex interactions between pathogenic Shiga toxin-producing E. coli, the resident microbiome, and host tissues. The determination of these interactions may provide insights into the unresolved issues regarding these pathogens.

Insights into the genome architecture and evolution of Shiga toxin encoding bacteriophages of Escherichia coli

Background

A total of 179 Shiga toxin-producing Escherichia coli (STEC) complete genomes were analyzed in terms of serotypes, prophage coding regions, and stx gene variants and their distribution. We further examined the genetic diversity of Stx-converting phage genomes (Stx phages), focusing on the lysis-lysogeny decision and lytic cassettes.

Results

We show that most STEC isolates belong to non-O157 serotypes (73 %), regardless the sources and geographical regions. While the majority of STEC genomes contain a single stx gene (61 %), strains containing two (35 %), three (3 %) and four (1 %) stx genes were also found, being stx2 the most prevalent gene variant. Their location is exclusively found in intact prophage regions, indicating that they are phage-borne. We further demonstrate that Stx phages can be grouped into four clusters (A, B, C and D), three subclusters (A1, A2 and A3) and one singleton, based on their shared gene content. This cluster distribution is in good agreement with their predicted virion morphologies. Stx phage genomes are highly diverse with a vast number of 1,838 gene phamilies (phams) of related sequences (of which 677 are orphams i.e. unique genes) and, although having high mosaicism, they are generally organized into three major transcripts. While the mechanisms that guide lysis–lysogeny decision are complex, there is a strong selective pressure to maintain the stx genes location close to the lytic cassette composed of predicted SAR-endolysin and pin-holin lytic proteins. The evolution of STEC Stx phages seems to be strongly related to acquiring genetic material, probably from horizontal gene transfer events.

Conclusions

This work provides novel insights on the genetic structure of Stx phages, showing a high genetic diversity throughout the genomes, where the various lysis-lysogeny regulatory systems are in contrast with an uncommon, but conserved, lytic system always adjacent to stx genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07685-0.

Prevalence and Epidemiology of Non-O157 Escherichia coli Serogroups O26, O103, O111, and O145 and Shiga Toxin Gene Carriage in Scottish Cattle, 2014-2015

Cattle are reservoirs for Shiga toxin Escherichia coli (STEC), bacteria shed in animal feces. Humans are infected through consumption of contaminated food or water and by direct contact, causing serious disease and kidney failure in the most vulnerable.

Cattle are a reservoir for Shiga toxin-producing Escherichia coli (STEC), zoonotic pathogens that cause serious clinical disease. Scotland has a higher incidence of STEC infection in the human population than the European average. The aim of this study was to investigate the prevalence and epidemiology of non-O157 serogroups O26, O103, O111, and O145 and Shiga toxin gene carriage in Scottish cattle. Fecal samples (n = 2783) were collected from 110 herds in 2014 and 2015 and screened by real-time PCR. Herd-level prevalence (95% confidence interval [CI]) for O103, O26, and O145 was estimated as 0.71 (0.62, 0.79), 0.43 (0.34, 0.52), and 0.23 (0.16, 0.32), respectively. Only two herds were positive for O111. Shiga toxin prevalence was high in both herds and pats, particularly for stx₂ (herd level: 0.99; 95% CI: 0.94, 1.0). O26 bacterial strains were isolated from 36 herds on culture. Fifteen herds yielded O26 stx-positive isolates that additionally harbored the intimin gene; six of these herds shed highly pathogenic stx₂-positive strains. Multiple serogroups were detected in herds and pats, with only 25 herds negative for all serogroups. Despite overlap in detection, regional and seasonal effects were observed. Higher herd prevalence for O26, O103, and stx₁ occurred in the South West, and this region was significant for stx₂ at the pat level (P = 0.015). Significant seasonal variation was observed for O145 prevalence, with the highest prevalence in autumn (P = 0.032). Negative herds were associated with Central Scotland and winter. Herds positive for all serogroups were associated with autumn and larger herd size and were not housed at sampling.

IMPORTANCE Cattle are reservoirs for Shiga toxin-producing Escherichia coli (STEC), bacteria shed in animal feces. Humans are infected through consumption of contaminated food or water and by direct contact, resulting in serious disease and kidney failure in the most vulnerable. The contribution of non-O157 serogroups to STEC illness was underestimated for many years due to the lack of specific tests. Recently, non-O157 human cases have increased, with O26 STEC of particular note. It is therefore vital to investigate the level and composition of non-O157 in the cattle reservoir and to compare them historically and by the clinical situation. In this study, we found cattle prevalence high for toxin, as well as for O103 and O26 serogroups. Pathogenic O26 STEC were isolated from 14% of study herds, with toxin subtypes similar to those seen in Scottish clinical cases. This study highlights the current risk to public health from non-O157 STEC in Scottish cattle.

Whole-genome sequencing analysis of uncommon Shiga toxin-producing Escherichia coli from cattle: Virulence gene profiles, antimicrobial resistance predictions, and identification of novel O-serogroups

Shiga toxin-producing E. coli (STEC) are major foodborne pathogens. While many studies have focused on the "top-7 STEC", little is known for minor serogroups. A total of 284 non-top-7 STEC strains isolated from cattle feces were subjected to whole-genome sequencing (WGS) to determine the serotypes, the presence of virulence genes and antimicrobial resistance (AMR) determinants. Nineteen typeable and three non-typeable serotypes with novel O-antigen loci were identified. Twenty-one AMR genes and point mutations in another six genes that conferred resistance to 10 antimicrobial classes were detected, as well as 46 virulence genes. The distribution of 33 virulence genes and 15 AMR determinants exhibited significant differences among serotypes (p < 0.05). Among all strains, 81.7% (n = 232) and 14.1% (n = 40) carried stx2 and stx1 only, respectively; only 4.2% (n = 12) carried both. Subtypes stx1a, stx1c, stx2a, stx2c, stx2d, and stx2g were identified. Forty-six strains carried eae and stx2a and therefore had the potential cause severe diseases; 47 strains were genetically related to human clinical strains inferred from a pan-genome phylogenetic tree. We were able to demonstrate the utility of WGS as a surveillance tool to characterize the novel serotypes, as well as AMR and virulence profiles of uncommon STEC that could potentially cause human illness.

PCR Primers for Screening Food for Verotoxin-Producing Escherichia coli, Inclusive of Three vt1 and Seven vt2 Subtypes

ABSTRACT

Verotoxin-producing Escherichia coli (VTEC; also known as Shiga toxin-producing E. coli) is a significant cause of foodborne illnesses around the world. Due to the serological and genomic diversity of VTEC, methods of detection for VTEC in food samples require detection of verotoxin or its gene vt (also known as stx). The current taxonomy of vt identifies three vt1 (a, c, d) and seven vt2 (a to g) subtypes. PCR detection of vt is convenient and rapid, but protocols may not detect all currently identified variants or subtypes of vt. The Health Canada Compendium of Analytical Methods protocol for the analysis of food for VTEC is MFLP-52. MFLP-52 includes a VT Screening PCR that is used to determine the presumptive presence of VTEC by the detection of vt in food enrichments and to differentiate VTEC from other isolates. The VT Screening PCR was developed prior to the establishment of the current vt taxonomy. An evaluation of VT Screening PCR for detection of the 10 established vt subtypes was performed, and it was discovered that the method could not detect subtypes vt1d and vt2f. Additional primers and a modified protocol were developed, and the modified VT Screening PCR was tested against an inclusivity panel of 50 VTEC strains, including representatives of 10 vt subtypes, and an exclusivity panel of 30 vt-negative E. coli from various sources, to ensure specificity. The reliability of MFLP-52 with the modified VT Screening PCR was assessed by analysis of four priority food matrices (ground beef, lettuce, cheese, and apple cider) inoculated with a VTEC strain at 2 to 5 CFU/25 g. The modified VT Screening PCR was determined to be able to detect all 10 vt subtypes and reliably detect the presence of VTEC in all tested food enrichments.

HIGHLIGHTS

Characterization of Non-O157 Shiga Toxin-Producing Escherichia coli Cultured from Cattle Farms in Xinjiang Uygur Autonomous Region, China, During 2016-2017

Most outbreaks of Shiga toxin-producing Escherichia coli (STEC) are attributed to consumption of contaminated foodstuffs including beef and dairy products. In this study, we evaluated the prevalence of non-O157 STEC cultured from beef and dairy cattle and collected in Xinjiang Uygur Autonomous Region in China. Results identified 67 non-O157 STEC recovered from the 793 samples including beef cattle (10.28%, 43/418) and dairy cattle (6.40%, 24/375). A total of 67 non-O157 STEC was sequenced allowing for in silico analyses of their serotypes, virulence genes, and identification of the corresponding multilocus sequence types (STs). Twenty-one O serogroups and nine H serotypes were identified and the dominant serotype identified was O22:H8. One stx1 subtype (stx1a) and four stx2 subtypes (2a, 2b, 2c, and 2d) were found in the 67 non-O157 STEC isolates. The results revealed that stx1a+stx2a-positive STEC isolates were predominant (32.83%, 22/67), followed by stx1a+stx2d (29.85%, 20/67) and stx2a alone (17.91%, 12/67). Non-O157 STEC isolates carried virulence genes ehxA (98.51%), subA (53.73%), and cdtB (17.91%). Of the four adherence-associated genes tested, eaeA was absent, whereas lpfA and iha were present in 67 and 55 non-O157 STEC isolates, respectively. The STEC isolates were divided into 48 pulsed-field gel electrophoresis patterns and 10 STs, and ST446 (O22:H8) was the dominant clone (22.38%). Our results revealed that there was a high genetic diversity among non-O157 STEC isolated from beef and dairy cattle, some of which have potential to cause human diseases.

Characterization of Shiga toxin-producing Escherichia coli isolated from Cattle and Sheep in Xinjiang province, China, using whole-genome sequencing

Shiga toxin-producing Escherichia coli (STEC) is an important food-borne pathogen capable of causing severe gastrointestinal diseases in humans. Cattle and sheep are the natural reservoir hosts of STEC strains. Previously, we isolated 56 STEC strains from anal and carcass swab samples of cattle and sheep in farms and slaughterhouses. In this study, we performed whole-genome sequencing of these isolates and determined their serotypes, virulence profiles, sequence types (STs) and genetic relationships. Our results showed that the 56 isolates belong to 20 different STs, 29 O:H serotypes and 8 stx subtype combinations. The highly prevalent serotypes for bovine and ovine isolates were O8:H25 and O87:H16, respectively. Five serotypes of cattle or sheep isolates are novel. The majority (63%) of cattle isolates contain stx1 + stx2, subtyped into stx1a, stx2a and stx2c. In contrast, most of the sheep isolates contain stx1 only, primarily subtyped into stx1a and stx1c. None of the isolates tested eae-positive, but virulence factors such as ehxA and espP were present with variable prevalence rates. The prevalence of saa (19.6%) and espP (12.5%) in cattle isolates is much higher than that in sheep isolates, whereas that of subA (34%), katP (14.3%) and ireA (28.6%) in sheep isolates is considerably higher than that in cattle isolates. Core-genome SNP analysis revealed that the majority of isolates could be clustered based on their serotypes or STs, whereas some clustering is associated with more than one ST or serotype. Five sheep isolates (4 belonging to ST675 and serotype O76:H19 and 1 belonging to ST25 and serotype O128:H2) share STs, serotypes and stx profiles with two hemolytic uremic syndrome-associated enterohemorrhagic E. coli (HUSEC) isolates; a cattle isolate belonging to the same ST as HUSEC isolate HUSEC001 contains all the nine virulence genes tested. These data suggest a potential of the six isolates for causing severe human infections. Collectively, we described the characteristics of cattle and sheep STEC isolates from Xinjiang, China, which may be utilized in comparative studies of other geographic regions and sources of isolation, and for surveillance as well.

Shiga Toxin-Producing Escherichia coli in Feces of Finisher Pigs: Isolation, Identification, and Public Health Implications of Major and Minor Serogroups†

ABSTRACT

Shiga toxin-producing Escherichia coli (STEC) are major foodborne human pathogens that cause mild to hemorrhagic colitis, which could lead to complications of hemolytic uremic syndrome. Seven serogroups, O26, O45, O103, O111, O121, O145, and O157, account for the majority of the STEC illnesses in the United States. Shiga toxins 1 and 2, encoded by stx1 and stx2, respectively, and intimin, encoded by eae gene, are major virulence factors. Cattle are a major reservoir of STEC, but swine also harbor them in the hindgut and shed STEC in the feces. Our objectives were to use a culture method to isolate and identify major and minor serogroups of STEC in finisher pig feces. Shiga toxin genes were subtyped to assess public health implications of STEC. Fecal samples (n = 598) from finisher pigs, collected from 10 pig flows, were enriched in E. coli broth and tested for stx1, stx2, and eae by a multiplex PCR (mPCR) assay. Samples positive for stx1 or stx2 gene were subjected to culture methods, with or without immunomagnetic separation and plating on selective or nonselective media, for isolation and identification of stx-positive isolates. The culture method yielded a total of 178 isolates belonging to 23 serogroups. The three predominant serogroups were O8, O86, and O121. The 178 STEC strains included 26 strains with stx1a and 152 strains with stx2e subtypes. Strains with stx1a, particularly in association with eae (O26 and O103), have the potential to cause severe human infections. All stx2-positive isolates carried the subtype stx2e, a subtype that causes edema disease in swine, but is rarely involved in human infections. Several strains were also positive for genes that encode for enterotoxins, which are involved in neonatal and postweaning diarrhea in swine. In conclusion, our study showed that healthy finisher pigs harbored and shed several serogroups of E. coli carrying virulence genes involved in neonatal diarrhea, postweaning diarrhea, and edema disease, but prevalence of STEC of public health importance was low.

HIGHLIGHTS

A Toxic Environment: a Growing Understanding of How Microbial Communities Affect Escherichia coli O157:H7 Shiga Toxin Expression

Enterohemorrhagic Escherichia coli (EHEC) strains, including E. coli O157:H7, cause severe illness in humans due to the production of Shiga toxin (Stx) and other virulence factors. Because Stx is coregulated with lambdoid prophage induction, its expression is especially susceptible to environmental cues. Infections with Stx-producing E. coli can be difficult to model due to the wide range of disease outcomes: some infections are relatively mild, while others have serious complications. Probiotic organisms, members of the gut microbiome, and organic acids can depress Stx production, in many cases by inhibiting the growth of EHEC strains. On the other hand, the factors currently known to amplify Stx act via their effect on the stx-converting phage. Here, we characterize two interactive mechanisms that increase Stx production by O157:H7 strains: first, direct interactions with phage-susceptible E. coli, and second, indirect amplification by secreted factors. Infection of susceptible strains by the stx-converting phage can expand the Stx-producing population in a human or animal host, and phage infection has been shown to modulate virulence in vitro and in vivo Acellular factors, particularly colicins and microcins, can kill O157:H7 cells but may also trigger Stx expression in the process. Colicins, microcins, and other bacteriocins have diverse cellular targets, and many such molecules remain uncharacterized. The identification of additional Stx-amplifying microbial interactions will improve our understanding of E. coli O157:H7 infections and help elucidate the intricate regulation of pathogenicity in EHEC strains.

Comparative Transcriptomics of Shiga Toxin-Producing and Commensal Escherichia coli and Cytokine Responses in Colonic Epithelial Cell Culture Infections

Ingestion of Shiga toxin-producing Escherichia coli (STEC) can result in a range of illness severity from asymptomatic to hemorrhagic colitis and death; thus risk assessment of STEC strains for human pathogenicity is important in the area of food safety. Illness severity depends in part on the combination of virulence genes carried in the genome, which can vary between strains even of identical serotype. To better understand how core genes are regulated differently among strains and to identify possible novel STEC virulence gene candidates that could be added to the risk assessment repertoire, we used comparative transcriptomics to investigate global gene expression differences between two STEC strains associated with severe illness and a commensal E. coli strain during in vitro intestinal epithelial cell (IEC) infections. Additionally, we compared a wide array of concomitant cytokine levels produced by the IECs. The cytokine expression levels were examined for a pattern representing STEC pathogenicity; however, while one STEC strain appeared to elicit a proinflammatory response, infection by the other strain produced a pattern comparable to the commensal E. coli. This result may be explained by the significant differences in gene content and expression observed between the STEC strains. RNA-Seq analysis revealed considerable disparity in expression of genes in the arginine and tryptophan biosynthesis/import pathways between the STEC strains and the commensal E. coli strain, highlighting the important role some amino acids play in STEC colonization and survival. Contrasting differential expression patterns were observed for genes involved in respiration among the three strains suggesting that metabolic diversity is a strategy utilized to compete with resident microflora for successful colonization. Similar temporal expression results for known and putative virulence genes were observed in the STEC strains, revealing strategies used for survival prior to and after initial adherence to IECs. Additionally, three genes encoding hypothetical proteins located in mobile genetic elements were, after interrogation of a large set of E. coli genomes, determined to likely represent novel STEC virulence factors.

Fallow Deer (Dama dama) as a Reservoir of Shiga Toxin-Producing Escherichia coli (STEC)

Shiga toxin-producing Escherichia (E.) coli (STEC) are responsible for the outbreaks of serious diseases in humans. Only a few reports on fallow deer as a reservoir of foodborne pathogens have been published to date. The purpose of this study was to determine the occurrence of STEC strains in the fallow deer population in Poland. In all, 94 fallow deer swabs were tested. Polymerase chain reaction (PCR) was performed to detect the virulence profile of stx1, stx2 and eae or aggR genes, to identify the subtypes of stx1 and stx2 genes and to perform O and H serotyping. STEC and attaching and effacing (AE)-STEC were identified in 13 isolates (13.83%). The most hazardous virulence profile was detected in three strains, namely stx2d serotype O103:HNM, eae/stx1a serotype O26:HNM and eae/stx1a serotype O157:H7. The predominant stx gene was stx2, which was identified in 76.92% of isolates. E. coli O157 was detected in 4/94 (4.26%). Other E. coli serogroups, O26, O103, O111 and O145, were identified in 14/94 fallow deer (14.89%). The present findings suggest that fallow deer are carriers of STEC/AE-STEC that are potentially pathogenic to humans.

Microbiological quality of raw drinking milk and unpasteurised dairy products: results from England 2013-2019

The aim of this study was to review microbiology results from testing >2500 raw drinking milk and dairy products made with unpasteurised milk examined in England between 2013 and 2019. Samples were collected as part of incidents of contamination, investigation of infections or as part of routine monitoring and were tested using standard methods for a range of both pathogens and hygiene indicators. Results from testing samples of raw cow's milk or cheese made from unpasteurised milk for routine monitoring purposes were overall of better microbiological quality than those collected during incident or investigations of infections. Results from routine monitoring were satisfactory for 62% of milks, 82% of cream, 100% of ice-cream, 51% of butter, 63% of kefir and 79% of cheeses, with 5% of all samples being considered potentially hazardous. Analysis of data from cheese demonstrated a significant association between increasing levels of indicator Escherichia coli with elevated levels of coagulase positive staphylococci and decreased probability of isolation of Shiga toxin-producing E. coli. These data highlight the public health risk associated with these products and provide further justification for controls applied to raw drinking milk and dairy products made with unpasteurised milk.

Immunization of mice with chimeric antigens displaying selected epitopes confers protection against intestinal colonization and renal damage caused by Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) cause diarrhea and dysentery, which may progress to hemolytic uremic syndrome (HUS). Vaccination has been proposed as a preventive approach against STEC infection; however, there is no vaccine for humans and those used in animals reduce but do not eliminate the intestinal colonization of STEC. The OmpT, Cah and Hes proteins are widely distributed among clinical STEC strains and are recognized by serum IgG and IgA in patients with HUS. Here, we develop a vaccine formulation based on two chimeric antigens containing epitopes of OmpT, Cah and Hes proteins against STEC strains. Intramuscular and intranasal immunization of mice with these chimeric antigens elicited systemic and local long-lasting humoral responses. However, the class of antibodies generated was dependent on the adjuvant and the route of administration. Moreover, while intramuscular immunization with the combination of the chimeric antigens conferred protection against colonization by STEC O157:H7, the intranasal conferred protection against renal damage caused by STEC O91:H21. This preclinical study supports the potential use of this formulation based on recombinant chimeric proteins as a preventive strategy against STEC infections.

Genetic diversity of the intimin gene (eae) in non-O157 Shiga toxin-producing Escherichia coli strains in China

Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen. The increasing incidence of non-O157 STEC has posed a great risk to public health. Besides the Shiga toxin (Stx), the adherence factor, intimin, coded by eae gene plays a critical role in STEC pathogenesis. In this study, we investigated the prevalence and polymorphisms of eae gene in non-O157 STEC strains isolated from different sources in China. Among 735 non-O157 STEC strains, eae was present in 70 (9.5%) strains. Eighteen different eae genotypes were identified in 62 eae-positive STEC strains with the nucleotide identities ranging from 86.01% to 99.97%. Among which, seven genotypes were newly identified in this study. The eighteen eae genotypes can be categorized into five eae subtypes, namely β1, γ1, ε1, ζ3 and θ. Associations between eae subtypes/genotypes and serotypes as well as origins of strains were observed in this study. Strains belonging to serotypes O26:H11, O103:H2, O111:H8 are associated with particular eae subtypes, i.e., β1, ε1, θ, respectively. Most strains from diarrheal patients (7/9, 77.8%) carried eae-β1 subtype, while most isolates from cattle (23/26, 88.5%) carried eae-ζ3 subtype. This study demonstrated a genetic diversity of eae gene in non-O157 STEC strains from different sources in China.

Variability in growth responses of non-O157 EHEC isolates in leafy vegetables, sprouted seeds and soil extracts occurs at the isolate level

Foods of plant origin are recognised as a major source of foodborne pathogens, in particular for Shigatoxigenic Escherichia coli (STEC). Most work for STEC and plant-based fresh produce has focused on the most prevalent outbreak serogroup, O157. However, non-O157 STEC is an emerging hazard, and as such it is important to characterise aspects within this group that reflect their ability to colonise alternative hosts and habitats relevant to horticultural production. Growth kinetics were quantified for a diverse set of clinical enterohaemorrhagic E. coli isolates in extracts made from different tissues of spinach, lettuce or sprouted seeds, or from soil, to represent association with ready-to-eat fresh produce production. For leafy vegetables, spinach apoplast supported the fastest rates of growth and lettuce root extracts generated the slowest growth rates. Growth rates were similar for the majority of isolates in fenugreek or alfalfa sprouted seed extracts. Monosaccharides were the major driver of bacterial growth. No correlations were found for growth rates between different serotypes or for Shigatoxin gene carriage. Thus, growth rates varied in a plant-dependent and isolate-dependent manner, for all plant or soil extracts tested, indicative of isolate-specific differences in metabolic flexibility. These findings are relevant for risk assessment of non-O157 STEC.

A Putative Microcin Amplifies Shiga Toxin 2a Production of Escherichia coli O157:H7

Escherichia coli O157:H7 is a foodborne pathogen implicated in various multistate outbreaks. It encodes Shiga toxin on a prophage, and Shiga toxin production is linked to phage induction. An E. coli strain, designated 0.1229, that amplified Stx2a production when cocultured with E. coli O157:H7 strain PA2 was identified. Growth of PA2 in 0.1229 cell-free supernatants had a similar effect, even when supernatants were heated to 100°C for 10 min, but not after treatment with proteinase K. The secreted molecule was shown to use TolC for export and the TonB system for import. The genes sufficient for production of this molecule were localized to a 5.2-kb region of a 12.8-kb plasmid. This region was annotated, identifying hypothetical proteins, a predicted ABC transporter, and a cupin superfamily protein. These genes were identified and shown to be functional in two other E. coli strains, and bioinformatic analyses identified related gene clusters in similar and distinct bacterial species. These data collectively suggest that E. coli 0.1229 and other E. coli strains produce a microcin that induces the SOS response in target bacteria. Besides adding to the limited number of microcins known to be produced by E. coli, this study provides an additional mechanism by which stx _2a expression is increased in response to the gut microflora.IMPORTANCE How the gut microflora influences the progression of bacterial infections is only beginning to be understood. Antibiotics are counterindicated for E. coli O157:H7 infections, limiting treatment options. An increased understanding of how the gut microflora directs O157:H7 virulence gene expression may lead to additional treatment options. This work identified E. coli strains that enhance the production of Shiga toxin by O157:H7 through the secretion of a proposed microcin. Microcins are natural antimicrobial peptides that target specific species, can act as alternatives to antibiotics, and mediate microbial competition. This work demonstrates another mechanism by which non-O157 E. coli strains may increase Shiga toxin production and adds to our understanding of microcins, a group of antimicrobials less well understood than colicins.

Top-Down Proteomic Identification of Shiga Toxin 1 and 2 from Pathogenic Escherichia coli Using MALDI-TOF-TOF Tandem Mass Spectrometry

Shiga-toxin-producing Escherichia coli (STEC) are a burden on agriculture and a threat to public health. Rapid methods are needed to identify STEC strains and characterize the Shiga toxin (Stx) they produce. We analyzed three STEC strains for Stx expression, using antibiotic induction, matrix-assisted laser desorption/ionization time-of-flight-time-of-flight (MALDI-TOF-TOF) mass spectrometry, and top-down proteomic analysis. E. coli O157:H- strain 493/89 is a clinical isolate linked to an outbreak of hemolytic uremic syndrome (HUS) in Germany in the late 1980s. E. coli O145:H28 strains RM12367-C1 and RM14496-C1 were isolated from an agricultural region in California. The stx operon of the two environmental strains were determined by whole genome sequencing (WGS). STEC strain 493/89 expressed Shiga toxin 2a (Stx2a) as identified by tandem mass spectrometry (MS/MS) of its B-subunit that allowed identification of the type and subtype of the toxin. RM12367-C1 also expressed Stx2a as identified by its B-subunit. RM14496-C1 expressed Shiga toxin 1a (Stx1a) as identified from its B-subunit. The B-subunits of Stx1 and Stx2 both have an intramolecular disulfide bond. MS/MS was obtained on both the disulfide-bond-intact and disulfide-bond-reduced B-subunit, with the latter being used for top-down proteomic identification. Top-down proteomic analysis was consistent with WGS.

High prevalence of non-O157 Shiga toxin-producing Escherichia coli in beef cattle detected by combining four selective agars

Background

Shiga toxin-producing Escherichia coli (STEC) are emerging foodborne pathogens that are public health concern. Cattle have been identified as the major STEC reservoir. In the present study, we investigated the prevalence and characteristics of STEC strains in beef cattle from a commercial farm in Sichuan province, China.

Results

Among 120 beef cattle fecal samples, stx genes were positive in 90% of samples, as assessed using TaqMan real-time PCR, and 87 (72.5%) samples were confirmed to yield at least one STEC isolate by culture using four selective agars, MacConkey, CHROMagar™ ECC, modified Rainbow® Agar O157, and CHROMagar™ STEC, from which 31, 32, 91, and 73 STEC strains were recovered, respectively. A total of 126 STEC isolates were selected and further characterized. Seventeen different O:H serotypes were identified, all of which belonged to the non-O157 serotypes. One stx₁ subtype (stx_1a) and three stx₂ subtypes (stx_2a, stx_2c, and stx_2d) were present among these isolates. The intimin encoding gene eae, and other adherence-associated genes (iha, saa, and paa) were present in 37, 125, 74, and 30 STEC isolates, respectively. Twenty-three isolates carried the virulence gene subA, and only one harbored both cnf1 and cnf2 genes. Three plasmid-origin virulence genes (ehxA, espP, and katP) were present in 111, 111, and 7 isolates, respectively. The 126 STEC isolates were divided into 49 pulsed-field gel electrophoresis (PFGE) patterns.

Conclusions

Our study showed that the joint use of the selective MacConkey and modified Rainbow® Agar O157 agars increased the recovery frequency of non-O157 STEC strains in animal feces, which could be applied to other samples and in regular STEC surveillance. Moreover, the results revealed high genetic diversity of non-O157 STEC strains in beef cattle, some of which might have the potential to cause human diseases.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1582-8) contains supplementary material, which is available to authorized users.

Carriage of Shiga toxin phage profoundly affects Escherichia coli gene expression and carbon source utilization

Background

Enterohemorrhagic Escherichia coli (E. coli) are intestinal pathogenic bacteria that cause life-threatening disease in humans. Their cardinal virulence factor is Shiga toxin (Stx), which is encoded on lambdoid phages integrated in the chromosome. Stx phages can infect and lysogenize susceptible bacteria, thus either increasing the virulence of already pathogenic bacterial hosts or transforming commensal strains into potential pathogens. There is increasing evidence that Stx phage-encoded factors adaptively regulate bacterial host gene expression. Here, we investigated the effects of Stx phage carriage in E. coli K-12 strain MG1655. We compared the transcriptome and phenotype of naive MG1655 and two lysogens carrying closely related Stx2a phages: ϕO104 from the exceptionally pathogenic 2011 E. coli O104:H4 outbreak strain and ϕPA8 from an E. coli O157:H7 isolate.

Results

Analysis of quantitative RNA sequencing results showed that, in comparison to naive MG1655, genes involved in mixed acid fermentation were upregulated, while genes encoding NADH dehydrogenase I, TCA cycle enzymes and proteins involved in the transport and assimilation of carbon sources were downregulated in MG1655::ϕO104 and MG1655::ϕPA8. The majority of the changes in gene expression were found associated with the corresponding phenotypes. Notably, the Stx2a phage lysogens displayed moderate to severe growth defects in minimal medium supplemented with single carbon sources, e.g. galactose, ribose, L-lactate. In addition, in phenotype microarray assays, the Stx2a phage lysogens were characterized by a significant decrease in the cell respiration with gluconeogenic substrates such as amino acids, nucleosides, carboxylic and dicarboxylic acids. In contrast, MG1655::ϕO104 and MG1655::ϕPA8 displayed enhanced respiration with several sugar components of the intestinal mucus, e.g. arabinose, fucose, N-acetyl-D-glucosamine. We also found that prophage-encoded factors distinct from CI and Cro were responsible for the carbon utilization phenotypes of the Stx2a phage lysogens.

Conclusions

Our study reveals a profound impact of the Stx phage carriage on E. coli carbon source utilization. The Stx2a prophage appears to reprogram the carbon metabolism of its bacterial host by turning down aerobic metabolism in favour of mixed acid fermentation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5892-x) contains supplementary material, which is available to authorized users.

Pathogenic potential to humans of Shiga toxin-producing Escherichia coli isolated from wild boars in Poland

The aim of the study was to investigate the presence of Shiga toxin-producing Escherichia coli (STEC) in the wild boar population of north-eastern Poland, and to evaluate the potential health risk associated with wild boars carrying STEC/AE-STEC strains. In Poland, the African Swine Fever (ASF) virus has been a growing problem in domestic pigs and wild boars, one of the main reservoirs of the virus, because of this hunters, veterinary practitioners and foresters thus face a greater risk of coming into contact with animals. Rectal swabs samples were obtained from 152 wild boars hunter-harvested in the 2017/2018 season (autumn-winter) in north-eastern Poland. The samples were enrichment in modified buffered peptone water. Polymerase chain reaction (PCR) assays were conducted to determine the virulence profile of stx1, stx2 and eae and aggR genes, identify subtypes of stx1 and stx2 genes, and perform O and H serotyping. STEC/AE-STEC virulence genes were detected in 43 isolates (28.29%): STEC in 17 isolates (11.18%) and AE-STEC in 26 isolates (17.11%), respectively. None of the tested isolates carried the aggR gene. The most dangerous AE-STEC virulence profile associated with HUS was found in 2 isolates (1.32%): stx1NS/stx2a/d/eae serotype ONT:H7 and stx2a/eae serotype O146:H7. Six of the 152 tested samples belonged to serogroup O157 (3.95%), including one AE-STEC isolate with virulence profile stx2g/eae and five EPEC isolates. The results of this study suggest that wild boars in north-eastern Poland can carry STEC/AE-STEC strains that are potentially pathogenic for humans. This is the first report documenting the virulence of STEC and AE-STEC isolates from wild boars in Poland.