Pathogenic potential of Shiga toxin-producing Escherichia coli strains of caprine origin: virulence genes, Shiga toxin subtypes, phylogenetic background and clonal relatedness

Occurrence, antibiotic resistance and molecular characterisation of Shiga toxin-producing Escherichia coli isolated from broiler chickens in Tunisia

1. Shiga toxin-producing Escherichia coli (STEC) strains are associated with disease outbreaks which cause a public health problem. The aim of this study was to determine the frequency of STEC strains, their virulence factors, phylogenetic groups and antimicrobial resistance profiles in broiler chickens.2. A total of 222 E.coli isolates were collected from the caecum of chickens intended to be slaughtered. Antibiotic susceptibility was tested against 21 antimicrobial agents and ESBL phenotype was assessed by double-disk synergy test. The presence of STEC virulence genes stx1, stx2,eaeA and ehxA was detected by PCR. The identification of STEC serogroups was realised by PCR amplification. Additive virulence genes, phylogenetic groups and integrons were examined among the STEC isolates.3. Out of 222 E.coli isolates, 72 (32%) were identified as STEC strains and the most predominant serogroups were O103, O145 and O157. Shiga toxin gene 1 (stx1) was found in 84.7% (61/72) of the STEC strains, and eae and stx2 were detected in 38.8% and 13.8%, respectively. The ESBL phenotype was documented in 48.6% (35/72) of isolates. Most of the isolates (90.3%) carried class 1 integron with the gene cassette encoding resistance to trimethoprim (dfrA) and streptomycin (aadA) in 31.9% of the isolates. Class 2 integron was identified in 36.1% of isolates.4. Broilers can be considered as a reservoir of STEC strains which have high virulence factors and integrons that might be transmitted to other chickens, environments and humans. It is important to undertake surveillance and efficient control measures in slaughterhouses and farms to control measures of STEC bacteria.

A Comprehensive Review on Shiga Toxin Subtypes and Their Niche-Related Distribution Characteristics in Shiga-Toxin-Producing E. coli and Other Bacterial Hosts

Shiga toxin (Stx), the main virulence factor of Shiga-toxin-producing E. coli (STEC), was first discovered in Shigella dysenteriae strains. While several other bacterial species have since been reported to produce Stx, STEC poses the most significant risk to human health due to its widespread prevalence across various animal hosts that have close contact with human populations. Based on its biochemical and molecular characteristics, Shiga toxin can be grouped into two types, Stx1 and Stx2, among which a variety of variants and subtypes have been identified in various bacteria and host species. Interestingly, the different Stx subtypes appear to vary in their host distribution characteristics and in the severity of diseases that they are associated with. As such, this review provides a comprehensive overview on the bacterial species that have been recorded to possess stx genes to date, with a specific focus on the various Stx subtype variants discovered in STEC, their prevalence in certain host species, and their disease-related characteristics. This review provides a better understanding of the Stx subtypes and highlights the need for rapid and accurate approaches to toxin subtyping for the proper evaluation of the health risks associated with Shiga-toxin-related bacterial food contamination and human infections.

Gb3-Coated Bovine Milk Exosomes as a Practical Neutralizer for Shiga Toxin

Shiga toxin (Stx) is associated with foodborne infections of some Shigella spp. and Shiga toxin-producing Escherichia coli (STEC), leading to life-threatening hemolytic uremic syndrome (HUS). Target-specific therapeutics against HUS are currently unavailable in clinical practice. Herein, we reported the construction and in vitro characterization of Gb3-coated bovine milk exosomes (Gb3-mExo) as a multivalent Shiga toxin neutralizer, utilizing the natural advantages of milk exosomes (mExo) in drug delivery and multivalent interactions between Stx and its receptor Gb3. Gb3-mExo constructs were achieved by conjugating mExo with the Gb3 derivatives containing stearic acid-derived lipid tail, which was prepared through an efficient chemoenzymatic approach. The constructs were able to potently neutralize the binding of the B subunit of Stx2 (Stx2B) to receptor Gb3 immobilized on the plate or expressed on model cells. General safety of the constructs was evidenced by the cytotoxicity analysis and hemolysis assay. In addition to the excellent stability under conventional storage and handling conditions, the construct can also retain most of its neutralization potency under gastrointestinal pH extremes, showing the potential for oral administration. Considering the natural availability and excellent biocompatibility of mExo, Gb3-mExo conjugates should prove to be a practical prophylactic and therapeutic for the Shiga toxin-related infections.

Phylogenetic group and virulence profile classification in Escherichia coli from distinct isolation sources in Mexico

Escherichia coli is a leading cause of human enteric diseases worldwide. The rapid and accurate causal agent identification to a particular source represents a crucial step in the establishment of safety and health measures in the affected human populations and would thus provide insights into the relationship of traits that may contribute for pathogen persistence in a particular reservoir. The objective of the present study was to characterize over two hundred E. coli strains from different isolation sources in Mexico by conducting a correspondence analysis to explore associations with the detected phylogenetic groups. The results indicated that E. coli strains, recovered from distinct sources in Mexico, were classified into phylogroups B1 (35.8%), A (27.8%), and D (12.3%) and were clustered to particular clades according to the predicted phylogroups. The results from correspondence analysis showed that E. coli populations from distinct sources in Mexico, belonging to different phylogroups, were not dispersed randomly and were associated with a particular isolation source. Phylogroup A was strongly associated with human sources, and the phylogroup B1 showed a significant relationship with food sources. Additionally, phylogroup D was also related to human sources. Phylogroup B2 was associated with herbivorous and omnivorous mammals. Moreover, common virulence genes in the examined E. coli strains, assigned to all phylogroups, were identified as essential markers for survival and invasion in the host. Although virulence profiles varied among the detected phylogroups, E. coli strains belonging to phylogroup D, associated with humans, were found to contain the largest virulence gene repertoire conferring for persistence and survival in the host. In summary, these findings provide fundamental information for a better characterization of pathogenic E. coli, recovered from distinct isolation sources in Mexico and would assist in the development of better tools for identifying potential transmission routes of contamination.

Prevalence and Virulent Gene Profiles of Sorbitol Non-Fermenting Shiga Toxin-Producing Escherichia coli Isolated from Goats in Southern Thailand

Shiga toxin-producing Escherichia coli (STEC) is the pathogenic E. coli causing disease in humans via the consumption or handling of animal food products. The high prevalence of these organisms in ruminants has been widely reported. Among STECs, O157 is one of the most lethal serotypes causing serious disease in humans. The present study investigated the prevalence of sorbitol non-fermenting STECs in goats reared in the lower region of southern Thailand and described the virulent factors carried by those isolates. Sorbitol non-fermenting (SNF)-STECs were found in 57 out of 646 goats (8.82%; 95% CI 6.75% to 11.28%). Molecular identification revealed that 0.77% of SNF-STEC isolates were the O157 serotype. Shiga toxin genes (stx1 and stx2) and other virulent genes (i.e., eaeA, ehxA, and saa) were detected by molecular techniques. The presence of stx1 (75.44%) was significantly higher than that of stx2 (22.81%), whereas 1.75% of the total isolates carried both stx1 and stx2. Most of the isolates carried ehxA for 75.44%, followed by saa (42.11%) and eaeA (12.28%). In addition, 21.05% of STEC isolates did not carry any eaeA, ehxA, or saa. The first investigation on SNF-STECs in goat was conducted in the lower region of southern Thailand. The present study revealed that goats could be one of the potential carriers of SNF-STECs in the observing area.

Shiga Toxin Subtypes, Serogroups, Phylogroups, RAPD Genotypic Diversity, and Select Virulence Markers of Shiga-Toxigenic Escherichia coli Strains from Goats in Mid-Atlantic US

Understanding Shiga toxin subtypes in E. coli from reservoir hosts may give insight into their significance as human pathogens. The data also serve as an epidemiological tool for source tracking. We characterized Shiga toxin subtypes in 491 goat E. coli isolates (STEC) from the mid-Atlantic US region (stx1 = 278, stx2 = 213, and stx1/stx2 = 95). Their serogroups, phylogroups, M13RAPD genotypes, eae (intimin), and hly (hemolysin) genes were also evaluated. STEC-positive for stx1 harbored Stx1c (79%), stx1a (21%), and stx a/c (4%). Those positive for Stx2 harbored stx2a (55%) and Stx2b (32%), while stx2a/stx2d and stx2a/stx2b were each 2%. Among the 343 STEC that were serogrouped, 46% (n = 158) belonged to O8, 20% (n = 67) to 076, 12% (n = 42) to O91, 5% (n = 17) to O5, and 5% (n = 18) to O26. Less than 5% belonged to O78, O87, O146, and O103. The hly and eae genes were detected in 48% and 14% of STEC, respectively. Most belonged to phylogroup B1 (73%), followed by D (10%), E (8%), A (4%), B2 (4%), and F (1%). M13RAPD genotyping revealed clonality of 091, O5, O87, O103, and O78 but higher diversity in the O8, O76, and O26 serogroups. These results indicate goat STEC belonged to important non-O157 STEC serogroups, were genomically diverse, and harbored Shiga toxin subtypes associated with severe human disease.

Occurrence, Serotypes and Virulence Characteristics of Shiga-Toxin-Producing Escherichia coli Isolates from Goats on Communal Rangeland in South Africa

Shiga-toxin-producing Escherichia coli is a foodborne pathogen commonly associated with human disease characterized by mild or bloody diarrhea hemorrhagic colitis and hemolytic uremic syndrome. This study investigated the occurrence of STEC in fecal samples of 289 goats in South Africa using microbiological culture and PCR. Furthermore, 628 goat STEC isolates were characterized by serotype (O:H) and major virulence factors by PCR. STEC was found in 80.2% (232/289) of goat fecal samples. Serotyping of 628 STEC isolates revealed 63 distinct serotypes including four of the major top seven STEC serogroups which were detected in 12.1% (35/289) of goats: O157:H7, 2.7% (8/289); O157:H8, 0.3%, (1/289); O157:H29, 0.3% (1/289); O103:H8, 7.6% (22/289); O103:H56, 0.3% (1/289); O26:H2, 0.3% (1/289); O111:H8, 0.3% (1/289) and 59 non-O157 STEC serotypes. Twenty-four of the sixty-three serotypes were previously associated with human disease. Virulence genes were distributed as follows: stx1, 60.6% (381/628); stx2, 72.7% (457/628); eaeA, 22.1% (139/628) and hlyA, 78.0% (490/628). Both stx1 and stx2 were found in 33.4% (210/628) of isolates. In conclusion, goats in South Africa are a reservoir and potential source of diverse STEC serotypes that are potentially virulent for humans. Further molecular characterization will be needed to fully assess the virulence potential of goat STEC isolates and their capacity to cause disease in humans.

First Isolation and Molecular Characterization of bla CTX-M-121 -Producing Escherichia coli O157:H7 From Cattle in Xinjiang, China

The bovine Escherichia coli O157:H7 is a major foodborne pathogen causing severe bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome in humans. Cattle are recognized major reservoir and source of E. coli O157:H7. We investigated the antibiotic resistance, molecular profiles, and intrinsic relationship between 21 isolates of E. coli O157:H7 from cattle farms and slaughtering houses in Xinjiang. Using pulsed-field gel electrophoresis (PFGE) molecular typing, two types of PFGE were revealed through cluster analysis, including clusters I and II, with 66 and 100% similarity of PFGE spectra between 21 isolates. We also detected that 18 isolates (86%) carried at least one virulence gene, 16 isolates (76%) carried the eae gene, and 7 (33%) carried the stx1 + stx2 + eae + hly + tccp genes. Eighteen isolates were susceptible to antibiotics. Three isolates were resistant to antibiotics, and two were multidrug resistant. One of the two multidrug-resistant isolates detectably carried the bla CTX-M-121 gene. This is the first finding of the bla CTX-M-121 gene detected in E. coli O157:H7 isolated from cattle in Xinjiang. The bla CTX-M-121 gene is transferable between the bacterial strains via plasmid transmission. The results indicated that E. coli O157:H7 may have undergone clonal propagation in cattle population and cross-regional transmission in Xinjiang, China.

Age related differences in phylogenetic diversity, prevalence of Shiga toxins, Intimin, Hemolysin genes and select serogroups of Escherichia. coli from pastured meat goats detected in a longitudinal cohort study

Background

Little is known on significance, diversity and characteristics of gut E. coli in goats despite their importance as food animals globally. We characterized the temporal dynamics in diversity of E. coli in fecal samples from a cohort of goat kids and adult meat goats on pasture over a one-year period. Isolates were characterized based on phylogenetic grouping, virulence genes; shiga toxins 1 and 2 (Stx1&Stx2) (STEC), intimin (eaeA), hemolysin (hly) and select important sero-groups (026, 045, 0103, 0126 and 0146) using molecular methods.

Results

A total of 516 E. coli isolates were screened. Prevalence of virulence genes and STEC was 65 and 56% respectively. Prevalence of virulence genes and STEC was significantly higher in goat kids less than six months (76% /66%) than adults (48% /28%). Isolates with virulence profiles of two or more genes were also higher in young goat kids (50%) than adults (20%). Entero-pathogenic E. coli (EPEC-eaeA gene only) were mostly from pre-weaned goat kids while hly gene only isolates were significantly higher in adults. The stx1, stx2 and hly genes peaked around weaning (60, 63 and 52%) respectively. Goats kids were mostly hosts to group D (59%) while adults older than one year had B1 (75%) isolates. Group D isolates were most abundant at weaning (64%) and diarrhea samples (74%). Group B2 isolates overall (6%) were mostly detected around weaning (63%) while A isolates were 4% overall. Twenty-four isolates belonged to sero-groups 026, 0103 and 0146 with 70% of the isolates detected around weaning. Nineteen of these isolates were STEC with most harboring the stx1/stx2/hly/eae (25%) profile. Most belonged to O26 sero-group (75%) and phylogroup D (75%).

Conclusion

To our knowledge this is the first study to highlight longitudinal age related differences in E. coli phylogenetic diversity, abundance of virulence genes and select important sero-groups in goats. Differences detected suggest a possible role of age and weaning stress in influencing E. coli diversity in the gut of goats. The findings are relevant to both animal and public health to advise on further studies on caprine E. coli isolates as animal and human pathogens.

Public health aspects of Shiga toxin-producing Escherichia coli (STEC) strains in sheep and goats of Bakhtiari pastoral tribe, Iran

Nomadic populations do not have permanent settlements as they move their livestock between grazing areas in different seasons; such movements may have great impact on dissemination of food-borne pathogens in various regions. The aim of this study was to characterize Shiga toxin-producing Escherichia coli (STEC) strains as a food-borne pathogen in sheep and goats of Bakhtiari pastoral tribe in Iran. In the present study, 72 fecal samples were obtained from 26 sheep and 46 goats. First, all recovered E. coli isolates were screened for stx gene. After detection of stx-positive isolates, the virulence genes including stx1, stx2, eae, ehly, saa, astA, subAB, terD, and the genetic markers of O Island 57 (Z2098 and Z2099) were investigated. Also fifteen important STEC O-serogroups were determined using PCR assays. Results showed that 27 animals (27/72; 37.5%) carried STEC strains including 16/26 (61.6%) sheep and 11/46 (23.9%) goats. All STECs were eae-negative but 81.4% (22/27) were positive for saa. The most prevalent virulence profile was stx1/stx2/ehly/saa/subAB (37%; 10/27). Most STECs (24/27) were positive for at least one of the selected OI-57 markers. The O91 (n = 6), O5 (n = 3), O113 (n = 1), O128 (n = 1), and O104 (n = 1) were the detected O-serogroups in this study. It is concluded that such moving animal populations could have public health concerns which have to be addressed in the future.

Domestic and game pigeons as reservoirs for Escherichia coli harbouring antimicrobial resistance genes

OBJECTIVES

In Iran, pigeons are kept and bred on the roofs of houses, which indicates the potential significance of pigeons in the dispersal of antimicrobial resistant Escherichia coli strains. Here we characterized antimicrobial resistance genotypes in relation to phenotypic presentations and phylogenetic backgrounds of the E. coli isolates from household pigeons in Kerman in southeast Iran.

METHODS

Totally, 152 faecal E. coli isolates from domestic and household pigeons were screened for 13 antimicrobial resistance genes, bla_TEM, bla_SHV, bla_CTX-M, sulI, sulII, dhfrI, dhfrV, aadA, aac(3)-I, tetA, tetB, floR and qnrA, by conventional polymerase chain reaction (PCR) technique. Clermont phylogenetic background of E. coli strains was studied and antibiotic resistance of all strains was assessed for seven antibiotics.

RESULTS

The antimicrobial resistance genes bla_TEM, tetA, tetB and aadA were detected in 52.6%, 6.5%, 6.5% and 5.9% of the isolates, respectively. PCR phylotyping revealed that a significant number of isolates within A₀ (54%), A₁ (70%), B1 (57.6%), B2₂ (75%) and D1 (87.5%) phylogroups were positive for the studied resistance genes. One phenotypic resistance pattern (trimethoprim-sulfamethoxazole) was associated with the presence of the corresponding gene sul2.

CONCLUSIONS

An alarming rate of phenotypic resistance was observed in this study. Many isolates were positive for the screened resistance genes. According to the phylogenetic background, most resistant isolates belonged to the commensal phylotypes, representing significant role of commensal strains as a source of resistance genes. These findings highlight the role of the pigeon as disseminator of resistant E. coli strains.

Molecular detection of Shiga toxin-producing and antibiotic-resistant Escherichia coli isolates from buffaloes in southwest of Iran

Three hundred fifteen bacteriological samples were obtained from feces and both external and visceral cavity surfaces of carcasses of 105 healthy buffalo slaughtered in southwest of Iran. Confirmed Escherichia coli isolates were examined for antimicrobial resistance phenotypically and were screened for stx₁, stx₂, and eae genes and their subtypes and assessment of antimicrobial resistance genes by regular PCR and RFLP techniques. One hundred forty-five E. coli were isolated from feces (96 isolates) and external (37) and internal (12) surfaces of carcasses. Results showed that the prevalence of STEC, EPEC, and EHEC pathotypes was 2.8%, 0.7%, and 0.7% respectively. Among 6 (4.13%) positive isolates for examined genes, 4 (2.8%) isolates were positive for stx1, 3 (2.1%) for stx2, and 2 (1.4%) for eae gene. The detected genes were classified into stx₁a (4 isolates), stx₂a, stx₂b, stx₂c, eae-β, and unknown subtypes. The most prevalent antibiotic resistance gene was sulII (11.03%). The tetB, qnrB, floR, bla_TEM, bla_SHV, and aad_A genes were found to a lesser extent, and all isolates were negative for bla_CTX-15, bla_OXA, aac(3)-I, tetA, cat1, qnrA, sulI, dhfrI, and dhfrV genes. Twelve combination patterns of antibiotic-resistant genes were observed. Maximum phenotypically resistance rate was against doxycycline (91.83%), and the minimum was against ceftazidime and florfenicol (2.75%). E. coli isolates from feces and carcasses of slaughtered buffalo can be considered a mild reservoir for stx and eae genes. However, healthy buffaloes could be considered a potential reservoir of multiple antibiotic resistance genes in E. coli isolates.

An investigation of shedding and super-shedding of Shiga toxigenic Escherichia coli O157 and E. coli O26 in cattle presented for slaughter in the Republic of Ireland

Shiga toxigenic Escherichia coli (STEC) are an important group of pathogens and can be transmitted to humans from direct or indirect contact with cattle faeces. This study investigated the shedding of E. coli O157 and O26 in cattle at the time of slaughter and factors associated with super-shedding (SS) animals. Rectoanal mucosal swab (RAMS) samples were collected from cattle (n = 1,317) at three large Irish commercial beef abattoirs over an 18 month period, and metadata were collected at the time of sampling regarding farm of origin, animal age, breed and gender. RAMS swabs were examined for the presence and numbers of E. coli O157 and O26 using a previously developed quantitative real-time PCR protocol. Samples positive by PCR were culturally examined and isolates analysed for the presence of stx subtypes, eae and phylogroup. Any samples with counts >10⁴  CFU/swab of STEC O157 or O26 were deemed to be super-shedders. Overall, 4.18% (55/1,317) of RAMS samples were positive for STEC O157, and 2.13% (28/1,317) were classified as STEC O157 SS. For STEC O26, 0.76% (10/1,317) of cattle were positive for STEC O26, and 0.23% (3/1,317) were classified as super-shedders. Fewer STEC shedders and SS were noted among older animals (>37 months). There was a seasonal trend observed for STEC O157, with the highest prevalence of shedding and SS events in the autumn (August to October). The majority of E. coli O157 (50/55) isolates had stx2 and were eae positive, with no significant difference between SS and low shedders (LS). Interestingly, all STEC O26 (n = 10) were eae negative and had varied stx profiles. This study demonstrates that, while the overall shedding rates are relatively low in cattle at slaughter, among positive animals there is a high level of SS, which may pose a higher risk of cross-contamination during slaughter.