Serotypes and virulence profiles of Shiga toxin-producing Escherichia coli strains isolated during 2017 from human infections in Switzerland

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.

Clonal spread of non-O157 Shiga toxigenic Escherichia coli O21:H25 in raw water buffalo milks

AIMS

This study was conducted to investigate the presence of Shiga toxin-producing O157 and non-O157 E. coli in raw water buffalo milk, as well as to determine the virulence gene profiles, phylogroups, sequence types, and serotypes of the isolated strains.

METHODS AND RESULTS

A total of 200 hand-milked raw water buffalo milk samples were collected from 200 different water buffaloes over a period of three months from 20 different farms. Isolation of STEC was performed using CHROMagar STEC. Presence of stx1, stx2, and eaeA genes were investigated by mPCR. Phylogroups and sequence types of E. coli strains were determined by Clermont phylotyping and MLST. Serotyping was performed using PCR or WGS. According to the results, two milk samples obtained from two different farms were found as STEC-positive. All Stx-positive E. coli isolates belonged to phylogenetic group A and were assigned to ST10. WGS results indicated that serotype of two isolates was O21:H25 and average nucleotide identity was detected at 99.99%. Thirteen additional registered E. coli O21:H25 assembled WGS data were obtained from EnteroBase and a phylogenetic tree was constructed.

CONCLUSIONS

With this study, the presence of stx2 harboring E. coli O21:H25 in milk was identified for the first time. Although the identified serotype is considered a non-pathogen seropathotype, we conclude it could play an important role in the environmental circulation of Stx-phages and consequently contribute to the emergence of new STEC-related outbreaks.

Prevalence and In Vivo Assessment of Virulence in Shiga Toxin-Producing Escherichia coli Clinical Isolates from Greater Cairo Area

Background: Shiga toxin-producing Escherichia coli (STEC) has been identified as an important etiologic agent of human disease in Egypt. Aims: To investigate the occurrence and describe the characterization as well as prevalence of STEC in Greater Cairo hospitals as well as molecular characterization of virulence and resistance genes. Methods: Four hundred seventy E. coli clinical isolates were collected from eight hospitals and analyzed by genotypic and phenotypic methods for STEC, followed by histopathological examination and scoring of different organs lesions. Results: The highest proportion of isolates was from urine (151 isolates), whereas the lowest was from splenic drain (3 isolates). In tandem, when serogrouping was performed, 15 serogroups were obtained where the most prevalent was O157 and the least prevalent was O151. All isolates were positive when screened for identity gene gad A, while only typable strains were screened for seven virulence genes stx1 (gene encoding Shiga toxin 1), stx2 (gene encoding Shiga toxin 2), tsh (gene encoding thermostable hemagglutinin), eaeA (gene encoding intimin), invE (gene encoding invasion protein), aggR (gene encoding aggregative adherence transcriptional regulator), and astA (aspartate transaminase) where the prevalence was 48%, 30%, 50%, 57%, 7.5%, 12%, and 58%, respectively. Of 254 typable isolates, 152 were STEC carrying stx1 or stx2 genes or both. Conclusions: Relying on in vivo comparison between different E. coli pathotypes via histopathological examination of different organs, E. coli pathotypes could be divided into mild virulent, moderate virulent, and high virulent strains. Statistical analysis revealed significant correlation between different serogroups and presence of virulence genes.

Virulence of Shigatoxigenic and Enteropathogenic Escherichia coli O80:H2 in Galleria mellonella Larvae: Comparison of the Roles of the pS88 Plasmids and STX2d Phage

The invasiveness properties of Shigatoxigenic and enteropathogenic Escherichia coli (STEC and EPEC) O80:H2 in humans and calves are encoded by genes located on a pS88-like ColV conjugative plasmid. The main objectives of this study in larvae of the Galleria mellonella moth were therefore to compare the virulence of eight bovine STEC and EPEC O80:H2, of two E. coli pS88 plasmid transconjugant and STX2d phage transductant K12 DH10B, of four E. coli O80:non-H2, and of the laboratory E. coli K12 DH10B strains. Thirty larvae per strain were inoculated in the last proleg with 10 μL of tenfold dilutions of each bacterial culture corresponding to 10 to 10⁶ colony-forming units (CFUs). The larvae were kept at 37 °C and their mortality rate was followed daily for four days. The main results were that: (i) not only the STEC and EPEC O80:H2, but also different E. coli O80:non-H2 were lethal for the larvae at high concentrations (from 10⁴ to 10⁶ CFU) with some variation according to the strain; (ii) the Stx2d toxin and partially the pS88 plasmid were responsible for the lethality caused by the E. coli O80:H2; (iii) the virulence factors of E. coli O80:non-H2 were not identified. The general conclusions are that, although the Galleria mellonella larvae represent a useful first-line model to study the virulence of bacterial pathogens, they are more limited in identifying their actual virulence properties.

Whole genome sequence-based characterisation of Shiga toxin-producing Escherichia coli isolated from game meat originating from several European countries

Game meat is becoming increasingly popular but may be contaminated with pathogenic bacteria such as Shiga toxin-producing Escherichia coli (STEC). STEC cause gastrointestinal illnesses including diarrhoea, haemorrhagic colitis (HC), and the haemolytic uremic syndrome (HUS). The aim of this study was to assess the occurrence of STEC in 92 meat samples from chamois (n = 2), red deer (n = 27), roe deer (n = 38), and wild boar (n = 25), from Switzerland and other European countries. After enrichment, Shiga-toxin encoding genes (stx) were detected by PCR in 78 (84%) of the samples and STEC were isolated from 23 (25%) of the same samples. Nine different serotypes and eight different sequence types (STs) were found, with O146:H28 ST738 (n = 10) and O110:H31 ST812 (n = 5) predominating. None of the STEC belonged to the so-called top-five serogroups O26, O103, O111, O145, and O157. Subtyping of stx identified stx1c (n = 9), stx2a (n = 1), stx2b (n = 19), stx2e (n = 2), and stx2g (n = 1). Additional virulence factors (VFs) comprised ehx (n = 12), iha (n = 21), sta1 (n = 1), and subAB (n = 19). None of the isolates contained the eae gene. Twenty-one STEC contained VFs associated with extra-intestinal pathogenic E. coli (ExPEC). Overall, the pathogenic potential of STEC in game meat is moderate, though the isolation of one STEC strain carrying stx2a, and of STEC/ExPEC hybrids suggests a role of game meat as a potential source of STEC infections in humans. Therefore, detailed knowledge of the safe handling and preparation of game meat is needed to prevent foodborne infections.

[Assessment of available and currently applied typing methods of zoonotic pathogens using the example of Shiga toxin-producing and enterohemorrhagic Escherichia coli (STEC/EHEC)]

INTRODUCTION

In order to improve patient care and to increase food safety within the framework of One Health, the project "Integrated Genomic Surveillance of Zoonotic Agents (IGS-Zoo)" aims to develop concepts for a genomic surveillance of Shiga toxin(Stx)-producing and enterohemorrhagic Escherichia coli (STEC/EHEC) in Germany.

METHODS

An online survey was conducted to assess the currently available and applied STEC/EHEC typing methods in the federal laboratories of veterinary regulation, food control, and public health service.

RESULTS

Twenty-six questionnaires from 33 participants were evaluated with regard to STEC/EHEC. The number of STEC/EHEC-suspected samples that the laboratories process per year ranges between 10 and 3500, and out of these they obtain between 3 and 1000 pathogenic isolates. Currently the most frequently used typing method is the determination of Stx- and intimin-coding genes using polymerase chain reaction (PCR). Whole genome sequencing (WGS) is currently used by eight federal state laboratories, and nine are planning to implement it in the future. The most common obstacle for further typing of STEC/EHEC is that isolation from sample material is often unsuccessful despite apparent PCR detection of the stx genes.

DISCUSSION

The results of the survey should facilitate the integration of the analysis methods developed in the project and emphasize the target groups' individual needs for corresponding training concepts.

Impact of Shiga-toxin encoding gene transduction from O80:H2 Shiga toxigenic Escherichia coli (STEC) on non-STEC strains

Shiga toxin-producing Escherichia coli (STEC) are major foodborne pathogens that cause human diseases ranging from diarrhea to life-threatening complications including hemolytic-uremic syndrome. Virulence of STEC strains and their ability to cause severe diseases are associated with the activity of prophage-encoded Shiga toxins (Stxs). The first objective of this work was to isolate and characterize the Stx2d phage from STEC O80:H2 and to study the transfer of this phage in non-STEC strains. The second objective was to assess the survival of Galleria mellonella larvae inoculated with these transduced strains. Firstly, one bacteriophage isolated from a STEC O80:H2 strain was used to infect six non-STEC strains, resulting in the conversion of three strains. Then, stability assays were performed, showing that this phage was stable in the new STEC strains after three successive subculturing steps, as confirmed by a combination of short and long read genome sequencing approaches. This phage, vB_EcoS_ULI-O80_Stx2d, is resistant to moderate temperature and pH. It belongs to a currently unclassified genus and family within the Caudoviricetes class, shares 98% identity with Stx2_112808 phage and encodes several proteins involved in the lysogenic cycle. The yecE gene was identified at the insertion site. Finally, G. mellonella experiments showed that the transduced strains caused significantly higher mortality rates than the corresponding non-STEC strains. In conclusion, this study showed that stx2d gene from O80:H2 E. coli can be transferred to non-STEC strains and contributes to their virulence.

Epidemiology of Non-O157 Shiga Toxin-Producing Escherichia coli in the Province of Alberta, Canada, from 2018 to 2021

Non-O157 serogroups contribute significantly to the burden of disease caused by Shiga toxin-producing Escherichia coli (STEC) and have been underrecognized by traditional detection algorithms. We described the epidemiology of non-O157 STEC in Alberta, Canada for the period of 2018 to 2021. All non-O157 STEC isolated from clinical samples were submitted for serotyping and qPCR targeting the stx₁ and stx₂ genes. A total of 729 isolates were identified. Increased detection occurred over the summer months, peaking in July. Patients 18 years and younger made up 42.4% of cases, with 31.1% in those 0–9 years of age. There was a slight female predominance (399/729, 54.7%) A total of 50 different serogroups were detected; the most common were O26 (30.3%), O103 (15.9%), O111 (12.8%), O121 (11.0%), O118 (3.3%) and O71 (2.9%). These six serogroups made up 76.2% of all isolates. In total, 567 (77.8%) were positive for stx₁, 114 (15.6%) were positive for stx₂ and 48 (6.6%) were positive for both stx₁ and stx₂. A wide variety of non-O157 serogroups have been detected in Alberta, with the most frequent serogroups differing from other locations. These results highlight the need for further characterization of their virulence factors and clinical impact.

Characterisation of atypical Shiga toxin gene sequences and description of Stx2j, a new subtype

Shiga toxin (Stx) is the definitive virulence factor of Shiga toxin-producing Escherichia coli (STEC). Stx variants are currently organised into a taxonomic system of three Stx1 (a,c,d) and seven Stx2 (a,b,c,d,e,f,g) subtypes. In this study, seven STEC isolates from food and clinical samples possessing stx2 sequences that do not fit current Shiga toxin taxonomy were identified. Genome assemblies of the STEC strains was created from Oxford Nanopore and Illumina sequence data. The presence of atypical stx2 sequences were confirmed by Sanger sequencing, as were Stx2 expression and cytotoxicity. A strain of O157:H7 was found to possess stx1a and a truncated stx2a, which were originally misidentified as an atypical stx2. Two strains possessed unreported variants of Stx2a (O8:H28) and Stx2b (O146:H21). In four of the strains we found three Stx-subtypes that are not included in the current taxonomy. Stx2h (O170:H18) was identified in a Canadian sprout isolate; this subtype has only previously been reported in STEC from Tibetan Marmots. Stx2o (O85:H1) was identified in a clinical isolate. Finally, Stx2j (O158:H23 and O33:H14) was found in lettuce and clinical isolates. The results of this study expands the number of known Stx subtypes, the range of STEC serotypes, and isolation sources in which they may be found. The presence of the Stx2j and Stx2o in clinical isolates of STEC indicates that strains carrying these variants are potential human pathogens. Highlights Atypical Shiga toxin (stx) genes in Escherichia coli were sequenced. Two new variants of stx2a and stx2b are described. Two strains carried subtypes Stx2h and Stx2o, which have only one previous report. Two strains carried a previously undescribed subtype, Stx2j.

Distribution of virulence factors, antimicrobial resistance genes and phylogenetic relatedness among Shiga toxin-producing Escherichia coli serogroup O91 from human infections

Shiga toxin-producing Escherichia coli (STEC) belonging to the serogroup O91 are among the most common non-O157 STEC serogroups associated with human illness in Europe. This study aimed to analyse the virulence factors, antimicrobial resistance genes and phylogenetic relatedness among 48 clinical STEC O91 isolates collected during 2003-2019 in Switzerland. The isolates were subjected to whole genome sequencing using short-read sequencing technologies and a subset of isolates additionally to long-read sequencing. They belonged to O91:H10 (n=6), O91:H14 (n=40), and O91:H21 (n=2). Multilocus sequence typing showed that the O91:H10 isolates all belonged to sequence type (ST)641, while the O91:H14 isolates were assigned to ST33, ST9700, or were non-typeable. Both O91:H21 isolates belonged to ST442. Shiga toxin gene stx1a was the most common Shiga toxin gene subtype among the isolates, followed by stx2b, stx2d and stx2a. All isolates were LEE-negative and carried one or two copies of the IrgA adhesin gene iha. In a subset of long-read sequenced isolates, modules of the Locus of Adhesion and Autoaggregation pathogenicity island (LAA-PAI) carrying iha and other genes such as hes, lesP or agn43 were identified. A large proportion of STEC O91:H14 carried the subtilase cytotoxin gene subA, colicin genes (cba, cea, cib and cma) or microcin genes (mcmA, mchB, mchC and mchF). STEC O91:H14 were further distinguished from STEC O91:H10/H21 by one or more virulence factors found in extraintestinal pathogenic E. coli (ExPEC), including hlyF, iucC/iutA, kpsE and traT. The hlyF gene was identified on a novel mosaic plasmid that was unrelated to hlyF+ plasmids described previously in STEC. Core genome phylogenetic analysis revealed that STEC O91:H10 and STEC O91:H21 were clonally conserved, whereas STEC O91:H14 were clonally diverse. Among three STEC O91:H14 isolates, a number of resistance genes were identified, including genes that mediate resistance to aminoglycosides (aadA, aadA2, aadA9, aadA23, aph(3'')-Ib and aph(6)-Id), chloramphenicol (cmlA), sulphonamides (sul2 and sul3), and trimethoprim (drfA12). Our data contribute to understanding the genetic diversity and differing levels of virulence potential within the STEC O91 serogroup.

Hemolytic uremic syndrome associated with Shiga toxin-producing Escherichia coli infection in Argentina: update of serotypes and genotypes and their relationship with severity of the disease

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) infection is the most common cause of hemolytic uremic syndrome (HUS). Only few studies correlated serotypes and stx genotypes with disease severity. This study aimed to update STEC serotypes, stx genotypes, and virulence factors (eae and ehxA) in a cohort of patients with STEC-HUS and investigate whether they influence the severity of disease.

METHODS

In this multicentric study, children hospitalized between 2005 and 2016 with STEC-HUS confirmed by the National Reference Laboratory were included. Serotypes (O157, O145, O121, and others), stx genotypes (stx_1a, stx_2a, stx_2c, stx_2d, and others), and virulence factors were analyzed, and their association with dialysis requirement (>10 days); severe neurological, cardiovascular, and/or bowel involvement; and death was assessed.

RESULTS

The records of 280 patients were reviewed; 160 females, median age 21 months (IQR18m). STEC O157 was isolated in 206 (73.6%) patients, O145 in 47 (16.8%), O121 in 15 (5.4%), and other serotypes in 12 (4.2%). The stx_2a/_2c genotype was carried by 179 (63.9%) strains, stx_2a by 94 (33.6%), stx_1a/stx_2a by five (1.8%), and stx_1a only by two (0.7%). All strains except six harbored eae and ehxA genes. Fifty-nine (21.1%) patients had severe neurological involvement, 29 (10.4%) severe bowel injury, 14 (5%) cardiovascular involvement, 53 (18.9%) required > 10 days of dialysis, and 12 (4.3%) died. Neither serotypes nor stx genotypes detected were significantly linked to severity.

CONCLUSIONS

Serotype O157 and virulence stx_2a/2c, eae, ehxA genotype are prevalent in Argentina, and no relationship was found between severity and serotypes and genotypes of STEC detected.

High Occurrence of Shiga Toxin-Producing Escherichia coli in Raw Meat-Based Diets for Companion Animals-A Public Health Issue

Feeding pets raw meat-based diets (RMBDs) is becoming increasingly popular but comes with a risk of pathogenic bacteria, including Shiga toxin-producing Escherichia coli (STEC). In humans, STEC may cause gastrointestinal illnesses, including diarrhea, hemorrhagic colitis (HC), and the hemolytic uremic syndrome (HUS). The aim of this study was to evaluate commercially available RMBDs with regard to the occurrence of STEC. Of 59 RMBD samples, 59% tested positive by real-time PCR for the presence of Shiga toxin genes stx1 and/or stx2. STECs were recovered from 41% of the 59 samples, and strains were subjected to serotyping and virulence gene profiling, using whole genome sequencing (WGS)-based methods. Of 28 strains, 29% carried stx2a or stx2d, which are linked to STEC with high pathogenic potential. Twenty different serotypes were identified, including STEC O26:H11, O91:H10, O91:H14, O145:H28, O146:H21, and O146:H28, which are within the most common non-O157 serogroups associated with human STEC-related illnesses worldwide. Considering the low infectious dose and potential severity of disease manifestations, the high occurrence of STEC in RMBDs poses an important health risk for persons handling raw pet food and persons with close contact to pets fed on RMBDs, and is of concern in the field of public health.

Shiga Toxin-Associated Hemolytic Uremic Syndrome: Specificities of Adult Patients and Implications for Critical Care Management

Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome (STEC-HUS) is a form of thrombotic microangiopathy secondary to an infection by an enterohemorrhagic E. coli. Historically considered a pediatric disease, its presentation has been described as typical, with bloody diarrhea at the forefront. However, in adults, the clinical presentation is more diverse and makes the early diagnosis hazardous. In this review, we review the epidemiology, most important outbreaks, physiopathology, clinical presentation and prognosis of STEC-HUS, focusing on the differential features between pediatric and adult disease. We show that the clinical presentation of STEC-HUS in adults is far from typical and marked by the prevalence of neurological symptoms and a poorer prognosis. Of note, we highlight knowledge gaps and the need for studies dedicated to adult patients. The differences between pediatric and adult patients have implications for the treatment of this disease, which remains a public health threat and lack a specific treatment.

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.

Genetic diversity and pathogenic potential of Shiga toxin-producing Escherichia coli (STEC) derived from German flour

Shiga toxin-producing Escherichia coli (STEC) can cause severe human illness, which are frequently linked to the consumption of contaminated beef or dairy products. However, recent outbreaks associated with contaminated flour and undercooked dough in the United States and Canada, highlight the potential of plant based food as transmission routes for STEC. In Germany STEC has been isolated from flour, but no cases of illness have been linked to flour. In this study, we characterized 123 STEC strains isolated from flour and flour products collected between 2015 and 2019 across Germany. In addition to determination of serotype and Shiga toxin subtype, whole genome sequencing (WGS) was used for isolates collected in 2018 to determine phylogenetic relationships, sequence type (ST), and virulence-associated genes (VAGs). We found a high diversity of serotypes including those frequently associated with human illness and outbreaks, such as O157:H7 (stx2c/d, eae), O145:H28 (stx2a, eae), O146:H28 (stx2b), and O103:H2 (stx1a, eae). Serotypes O187:H28 (ST200, stx2g) and O154:H31 (ST1892, stx1d) were most prevalent, but are rarely linked to human cases. However, WGS analysis revealed that these strains, as well as, O156:H25 (ST300, stx1a) harbour high numbers of VAGs, including eae, nleB and est1a/sta1. Although STEC-contaminated flour products have yet not been epidemiologically linked to human clinical cases in Germany, this study revealed that flour can serve as a vector for STEC strains with a high pathogenic potential. Further investigation is needed to determine the sources of STEC contamination in flour and flour products particularly in regards to these rare serotypes.

Genomic Insights Into Clinical Shiga Toxin-Producing Escherichia coli Strains: A 15-Year Period Survey in Jönköping, Sweden

Shiga toxin-producing Escherichia coli (STEC) are important foodborne pathogens that can cause human infections ranging from asymptomatic carriage to bloody diarrhea (BD) and fatal hemolytic uremic syndrome (HUS). However, the molecular mechanism of STEC pathogenesis is not entirely known. Here, we demonstrated a large scale of molecular epidemiology and in-depth genomic study of clinical STEC isolates utilizing clinical and epidemiological data collected in Region Jönköping County, Sweden, over a 15-year period. Out of 184 STEC isolates recovered from distinct patients, 55 were from patients with BD, and 129 were from individuals with non-bloody stools (NBS). Five individuals developed HUS. Adults were more associated with BD. Serotypes O157:H7, O26:H11, O103:H2, O121:H19, and O104:H4 were more often associated with BD. The presence of Shiga toxin-encoding gene subtypes stx 2a, stx 2a + stx 2c, and stx 1a + stx 2c was associated with BD, while stx 1 a was associated with milder disease. Multiplex virulence and accessory genes were correlated with BD; these genes encode toxins, adhesion, autotransporters, invasion, and secretion system. A number of antimicrobial resistance (AMR) genes, such as aminoglycoside, aminocoumarin, macrolide, and fluoroquinolone resistance genes, were prevalent among clinical STEC isolates. Whole-genome phylogeny revealed that O157 and non-O157 STEC isolates evolved from distinct lineages with a few exceptions. Isolates from BD showed more tendency to cluster closely. In conclusion, this study unravels molecular trait of clinical STEC strains and identifies genetic factors associated with severe clinical outcomes, which could contribute to management of STEC infections and disease progression if confirmed by further functional validation.

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.

Do changes in STEC diagnostics mislead interpretation of disease surveillance data in Switzerland? Time trends in positivity, 2007 to 2016

BackgroundLaboratory-confirmed cases of Shiga toxin-producing Escherichia coli (STEC) have been notifiable to the National Notification System for Infectious Diseases in Switzerland since 1999. Since 2015, a large increase in case numbers has been observed. Around the same time, syndromic multiplex PCR started to replace other diagnostic methods in standard laboratory practice for gastrointestinal pathogen testing, suggesting that the increase in notified cases is due to a change in test practices and numbers.AimThis study examined the impact of changes in diagnostic methods, in particular the introduction of multiplex PCR panels, on routine STEC surveillance data in Switzerland.MethodsWe analysed routine laboratory data from 11 laboratories, which reported 61.9% of all STEC cases from 2007 to 2016 to calculate the positivity, i.e. the rate of the number of positive STEC tests divided by the total number of tests performed.ResultsThe introduction of multiplex PCR had a strong impact on STEC test frequency and identified cases, with the number of tests performed increasing sevenfold from 2007 to 2016. Still, age- and sex-standardised positivity increased from 0.8% in 2007 to 1.7% in 2016.ConclusionIncreasing positivity suggests that the increase in case notifications cannot be attributed to an increase in test numbers alone. Therefore, we cannot exclude a real epidemiological trend for the observed increase. Modernising the notification system to address current gaps in information availability, e.g. diagnostic methods, and improved triangulation of clinical presentation, diagnostic and serotype information are needed to deal with emerging disease and technological advances.

Utilization of Clustered Regularly Interspaced Short Palindromic Repeats to Genotype Escherichia coli Serogroup O80

The hypervariable nature of clustered regularly interspaced short palindromic repeats (CRISPRs) makes them valuable biomarkers for subtyping and epidemiological investigation of Escherichia coli. Shiga toxin-producing E. coli (STEC) serogroup O80 is one hybrid pathotype that is emerging recently in Europe and is involved in hemolytic uremic syndrome with bacteremia. However, whether STEC O80 strains can be genotyped using CRISPR has not been evaluated. In this study, we aimed to characterize the genetic diversity of 81 E. coli serogroup O80 isolates deposited in the National Center for Biotechnology Information databases using CRISPR typing and to explore the association between virulence potential and CRISPR types (CTs). A total of 21 CTs were identified in 80 O80 strains. CRISRP typing provided discrimination with variants of a single serotype, which suggested a stronger discriminatory power. Based on CRISPR spacer profiles, 70 O80:H2 isolates were further divided into four lineages (lineage LI, LII, LIII, and LIV), which correlated well with whole-genome single nucleotide polymorphisms typing and virulence gene profiles. Moreover, the association between CRISPR lineages and virulence gene profiles hinted that STEC O80:H2 strains may originate from O80:H19 or O80:H26 and that lineage LI may have been evolved from lineage LII. CT2 and CT13 were shared by human and cattle isolates, suggesting that there might be the potential transmission between cattle and human. Collectively, CRISPR typing is one technology that can be used to monitor the transmission of STEC O80 strains and provide new insights into microevolution of serogroup O80.

Isolate independent molecular typing improves the yield of O typing of infections due to Shiga toxin producing Escherichia coli

Molecular screening has increased detection of Shiga-toxin producing Escherichia coli (STEC). However, it is difficult to isolate the organism for epidemiological typing. We applied a molecular method for direct detection of nine O types from 110 stx positive faeces samples and compared the results with conventional isolate based methods. Using conventional methods 55/110 (50%) samples were O typed. Using the molecular method, 72/110 (65%) were O typed, including 23/38 (61%) culture negative samples. Combining both techniques typed 88/110 (80%) of samples. Molecular typing increased detection of O128 (2-25%, p<0.001), O26 (11-16%) O45 (0-6%) and O103 (1-6%) infections. Molecular typing of STEC direct from faecal samples improved O type yield; risk of bias in epidemiological and surveillance activities may be reduced by inclusion of culture independent typing methods.

Genome Sequences of Uncommon Shiga Toxin-Producing Escherichia coli Serotypes

Shiga toxin-producing Escherichia coli (STEC) is a foodborne disease with worldwide outbreaks. STEC serotypes O157, O26, O45, O103, O111, O121, and O145 cause the most outbreaks. There is little published information regarding the other serotypes. We report the draft genome sequences for 11 uncommon STEC serotypes from Nebraska.

Shiga toxin-producing Escherichia coli (STEC) is a foodborne disease with worldwide outbreaks. STEC serotypes O157, O26, O45, O103, O111, O121, and O145 cause the most outbreaks. There is little published information regarding the other serotypes. We report the draft genome sequences for 11 uncommon STEC serotypes from Nebraska.

Virulence Profiling and Molecular Typing of Shiga Toxin-Producing E. coli (STEC) from Human Sources in Brazil

Since no recent data characterizing Shiga toxin-producing E. coli (STEC) from human infections in Brazil are available, the present study aimed to investigate serotypes, stx genotypes, and accessory virulence genes, and also to perform pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) of 43 STEC strains recovered from 2007 to 2017. Twenty-one distinct serotypes were found, with serotype O111:H8 being the most common. However, serotypes less frequently reported in human diseases were also found and included a hybrid STEC/ETEC O100:H25 clone. The majority of the strains carried stx1a as the sole stx genotype and were positive for the eae gene. Regarding the occurrence of 28 additional virulence genes associated with plasmids and pathogenicity islands, a diversity of profiles was found especially among the eae-harboring strains, which had combinations of markers composed of up to 12 distinct genes. Although PFGE analysis demonstrated genetic diversity between serotypes such as O157:H7, O111:H8, O26:H11, O118:H16, and O123:H2, high genetic relatedness was found for strains of serotypes O24:H4 and O145:H34. MLST allowed the identification of 17 distinct sequence types (STs) with ST 16 and 21 being the most common ones. Thirty-five percent of the strains studied were not typeable by the currently used MLST approach, suggesting new STs. Although STEC O111:H8 remains the leading serotype in Brazil, a diversity of other serotypes, some carrying virulence genes and belonging to STs incriminated as causing severe disease, were found in this study. Further studies are needed to determine whether they have any epidemiological relevance.

Prediction, Diversity, and Genomic Analysis of Temperate Phages Induced From Shiga Toxin-Producing Escherichia coli Strains

Shiga toxin-producing Escherichia coli (STEC) is a notorious foodborne pathogen containing stx genes located in the sequence region of Shiga toxin (Stx) prophages. Stx prophages, as one of the mobile elements, are involved in the transfer of virulence genes to other strains. However, little is known about the diversity of prophages among STEC strains. The objectives of this study were to predict various prophages from different STEC genomes and to evaluate the effect of different stress factors on Stx prophage induction. Forty bacterial whole-genome sequences of STEC strains obtained from National Center for Biotechnology Information (NCBI) were used for the prophage prediction using PHASTER webserver. Eight of the STEC strains from different serotypes were subsequently selected to quantify the induction of Stx prophages by various treatments, including antibiotics, temperature, irradiation, and antimicrobial agents. After induction, Stx1-converting phage Lys8385Vzw and Stx2-converting phage Lys12581Vzw were isolated and further confirmed for the presence of stx genes using conventional PCR. Phage morphology was observed by transmission electron microscopy. The prediction results showed an average of 8–22 prophages, with one or more encoding stx, were predicted from each STEC genome obtained in this study. Additionally, the phylogenetic analysis revealed high genetic diversity of Stx prophages among the 40 STEC genomes. However, the sequences of Stx prophages in the genomes of STEC O45, O111, and O121 strains, in general, shared higher genetic homology than those in other serotypes. Interestingly, most STEC strains with two or more stx genes carried at least one each of Stx1 and Stx2 prophages. The induction results indicated EDTA and UV were the most effective inducers of Stx1 and Stx2 prophages of the 8 selected STECs, respectively. Additionally, both Stx-converting phages could infect non-pathogenic E. coli (WG5, DH5α, and MG1655) and form new lysogens. The findings of this study confirm that Stx prophages can be induced by environmental stress, such as exposure to solar radiation, and lysogenize other commensal E. coli strains.

Rapid culture-based identification of Shiga toxin-producing Escherichia coli and Shigella spp./Enteroinvasive E. coli using the eazyplex® EHEC complete assay

Shiga toxin-producing Escherichia coli (STEC) and Shigella spp./enteroinvasive E. coli (EIEC) are common diarrheagenic bacteria that cause sporadic diseases and outbreaks. Clinical manifestations vary from mild symptoms to severe complications. For microbiological diagnosis, culture confirmation of a positive stool screening PCR test is challenging because of time-consuming methods for isolation of strains, wide variety of STEC pathotypes, and increased emergence of non-classical strains with unusual serotypes. Therefore, molecular assays for the rapid identification of suspect colonies growing on selective media are very useful. In this study, the performance of the newly introduced eazyplex® EHEC assay based on loop-mediated isothermal amplification (LAMP) was evaluated using 18 representative STEC and Shigella strains and 31 isolates or positive-enrichment broths that were collected from clinical stool samples following screening by BD MAX™ EBP PCR. Results were compared to real-time PCR as a reference standard. Overall, sensitivities and specificities of the eazyplex® EHEC were as follows: 94.7% and 100% for Shiga toxin 1 (stx1), 100% and 100% for stx2, 93.3% and 97.1% for intimin (eae), 100% and 100% for enterohemolysin A (ehlyA), and 100% and 100% for invasion-associated plasmid antigen H (ipaH) as Shigella spp./EIEC target, respectively. Sample preparation for LAMP took only some minutes, and the time to result of the assay ranged from 8.5 to 13 min. This study shows that eazyplex® EHEC is a very fast and easy to perform molecular assay that provides reliable results as a culture confirmation assay for the diagnosis of STEC and Shigella spp./EIEC infections.

Cumulative acquisition of pathogenicity islands has shaped virulence potential and contributed to the emergence of LEE-negative Shiga toxin-producing Escherichia coli strains

Shiga toxin-producing Escherichia coli (STEC) are foodborne pathogens causing severe gastroenteritis, which may lead to hemolytic uremic syndrome. The Locus of Enterocyte Effacement (LEE), a Pathogenicity Island (PAI), is a major determinant of intestinal epithelium attachment of a group of STEC strains; however, the virulence repertoire of STEC strains lacking LEE, has not been fully characterized. The incidence of LEE-negative STEC strains has increased in several countries, highlighting the relevance of their study. In order to gain insights into the basis for the emergence of LEE-negative STEC strains, we performed a large-scale genomic analysis of 367 strains isolated worldwide from humans, animals, food and the environment. We identified uncharacterized genomic islands, including two PAIs and one Integrative Conjugative Element. Additionally, the Locus of Adhesion and Autoaggregation (LAA) was the most prevalent PAI among LEE-negative strains and we found that it contributes to colonization of the mice intestine. Our comprehensive and rigorous comparative genomic and phylogenetic analyses suggest that the accumulative acquisition of PAIs has played an important, but currently unappreciated role, in the evolution of virulence in these strains. This study provides new knowledge on the pathogenicity of LEE-negative STEC strains and identifies molecular markers for their epidemiological surveillance.

Whole Genome Sequencing Characterization of Shiga Toxin-Producing Escherichia coli Isolated from Flour from Swiss Retail Markets

Shiga toxin-producing Escherichia coli (STEC) strains are often found in food and cause human infections. Although STEC O157:H7 is most often responsible for human disease, various non-O157 subtypes have caused individual human infections or outbreaks. The importance of STEC serogroup typing is decreasing while detection of virulence gene patterns has become more relevant. Whole genome sequencing (WGS) reveals the entire spectrum of pathogen information, such as toxin variant, serotype, sequence type, and virulence factors. Flour has not been considered as a vector for STEC; however, this product has been associated with several STEC outbreaks in the last decade. Flour is a natural product, and milling does not include a germ-reducing step. Flour is rarely eaten raw, but the risks associated with the consumption of unbaked dough are probably underestimated. The aim of this study was to determine the prevalence of STEC in flour samples (n = 93) collected from Swiss markets and to fully characterize the isolates by PCR assay and WGS. The prevalence of STEC in these flour samples was 10.8% as indicated by PCR, and a total of 10 STEC strains were isolated (two flour samples were positive for two STEC subtypes). We found one stx₂-positve STEC isolate belonging to the classic serogroups frequently associated with outbreaks that could potentially cause severe disease. However, we also found several other common or less common STEC subtypes with diverse virulence patterns. Our results reveal the benefits of WGS as a characterization tool and that flour is a potentially and probably underestimated source for STEC infections in humans.

Polymorphism of Type I-F CRISPR/Cas system in Escherichia coli of phylogenetic group B2 and its application in genotyping

E. coli of phylogenetic group B2 is responsible for many extraintestinal infections, posing a great threat to health. The relatively polymorphic nature of CRISPR in phylogenetically related E. coli strains makes them potential markers for bacterial typing and evolutionary studies. In the current work, we investigated the occurrence and diversity of CRISPR/Cas system and explored its potential for genotyping. Type I-F CRISPR/Cas systems were found in 413 of 1190 strains of E. coli and exhibited the clustering within certain CCs and STs. And CRISPR spacer contents correlated well with MLST types. The divergence analysis of CRISPR showed stronger discriminatory power than MLST, and CRISPR polymorphism was instrumental for differentiating highly closely related strains. The timeline of spacer acquisition and deletion provided important information for inferring the evolution model between distinct serotypes. Identical spacer sequences were shared by strains with the same H-antigen type but not strains with the same O-antigen type. The homology between spacers and antibiotic-resistant plasmids demonstrated the role of Type I-F system in limiting the acquisition of antimicrobial resistance. Collectively, our data presents the dynamic nature of Type I-F CRISPR in E. coli of phylogenetic group B2 and provides new insights into the application of CRISPR-based typing in the species.

The epidemiology of Shiga toxin-producing Escherichia coli infections in the South East of England: November 2013-March 2017 and significance for clinical and public health

PURPOSE

This study describes the epidemiology of Shiga toxin-producing Escherichia coli (STEC) infections in a population in the South East of England.

METHODS

From 1 November 2013 to 31 March 2017 participating diagnostic laboratories reported Shiga toxin gene (stx) positive real-time PCR results to local public health teams. Stx positive faecal samples/isolates were referred to the Gastrointestinal Bacteria Reference Unit (GBRU) for confirmation by culture and typing by whole genome sequencing (WGS). Key clinical information was collected by public health teams.Results/Key findings. Altogether, 548 faecal specimens (420 were non-travel associated) were stx positive locally, 535 were submitted to the GBRU. STEC were isolated from 42 %, confirmed by stx PCR in 21 % and 37 % were PCR negative. The most common non-travel associated STEC serogroups were O157, O26, O146 and O91. The annualized incidence of confirmed STEC infections (PCR or culture) was 5.8 per 100 000. The ratio of O157 to non-O157 STEC serogroups was 1:7. The annualized incidence of non-O157 haemolytic uraemic syndrome-associated Escherichia coli (HUSEC) strains was 0.4 per 100 000. Bloody diarrhoea was reported by 58 % of cases infected with E. coli O157, 33 % of cases infected with non-O157 HUSEC strains and 12 % of other lower risk non-O157 strains. Overall, 76 % of non-O157 HUSEC isolates possessed the eae virulence gene.

CONCLUSIONS

HUSEC including serogroup O157 were uncommon and more likely to cause bloody diarrhoea than other STEC. The routine use of stx PCR testing can influence clinical management. Understanding the local epidemiology facilitates a proportionate public health response to STEC, based on clinical and microbiological characteristics including stx subtype(s).

Detection, Isolation, and Characterization of Shiga Toxin-Producing Escherichia coli in Flour

Wheat flour has recently been described as a novel vehicle for transmission of Shiga toxin-producing Escherichia coli (STEC). Very recently, an outbreak of STEC O121 and STEC O26 infections was linked to flour in the United States. The aim of the present study was to generate baseline data for the occurrence of STEC in flour samples from different retailers in Switzerland. In total, 70 flour samples were analyzed. After enrichment, the samples were screened for stx₁ and stx₂ by the Assurance GDS MPX ID assay. STEC strains were isolated and serotyped by the E. coli SeroGenoTyping AS-1 kit. The determination of stx subtypes was performed with conventional PCR amplification. Screening for eae, aggR, elt, and estIa/Ib was performed by real-time PCR. Nine (12.9%) of the flour samples tested positive for stx by PCR. STEC was recovered from eight (88.9%) of the positive samples. Two isolates were STEC O11:H48 harboring stx_1c/ stx_1d, two were O146:H28 containing stx_2b, one was O103:H2 containing stx_1a and eae, and three were O nontypeable: Ont:H12 ( stx_2a), Ont:H14 ( stx_2a/ stx_2g), and Ont:H31 ( stx_1c/ stx_1d). STEC O103 belongs to the "top five" serogroups of human pathogenic STEC in the European Union, and STEC O146 is frequently isolated from diseased humans in Switzerland. Our results show that flour may be contaminated with a variety of STEC serogroups. Consumption of raw or undercooked flour may constitute a risk for STEC infection.