Virulence factors of Shiga toxin-producing Escherichia coli and the risk of developing haemolytic uraemic syndrome in Norway, 1992-2013

In Silico Analysis of Shiga Toxin-Producing Escherichia coli O157:H7 Strains from Presumptive Super- and Low-Shedder Cattle

Cattle are the primary reservoir for STEC O157, with some shedding >104 CFU/g in feces, a phenomenon known as super-shedding (SS). The mechanism(s) responsible for SS are not understood but have been attributed to the environment, host, and pathogen. This study aimed to compare genetic characteristics of STEC O157 strains from cattle in the same commercial feedlot pens with SS or low-shedding (LS) status. Strains from SS (n = 35) and LS (n = 28) collected from 11 pens in three feedlots were analyzed for virulence genes, Shiga toxin-carrying bacteriophage insertion sites, and phylogenetic relationships. In silico analysis showed limited variation regarding virulence gene profiles. Stx-encoding prophage insertion sites mrlA and wrbA for stx1a and stx2a, respectively, were all occupied, but two isolates had fragments of the stx-carrying phage in mrlA and wrbA loci without stx1a and stx2a. All strains screened for lineage-specific polymorphism assay (LSPA-6) were 111111, lineage I. Of the isolates, 61 and 2 were clades 1 and 8, respectively. Phylogenetic analysis revealed that pens with more than one SS had multiple distantly related clusters of SS and LS isolates. Although virulence genes and lineage were largely similar within and across feedlots, multiple genetic origins of strains within a single feedlot pen illustrate challenges for on-farm control of STEC.

Transforming Shiga toxin-producing Escherichia coli surveillance through whole genome sequencing in food safety practices

Introduction

Shiga toxin-producing Escherichia coli (STEC) is a gastrointestinal pathogen causing foodborne outbreaks. Whole Genome Sequencing (WGS) in STEC surveillance holds promise in outbreak prevention and confinement, in broadening STEC epidemiology and in contributing to risk assessment and source attribution. However, despite international recommendations, WGS is often restricted to assist outbreak investigation and is not yet fully implemented in food safety surveillance across all European countries, in contrast to for example in the United States.

Methods

In this study, WGS was retrospectively applied to isolates collected within the context of Belgian food safety surveillance and combined with data from clinical isolates to evaluate its benefits. A cross-sector WGS-based collection of 754 strains from 1998 to 2020 was analyzed.

Results

We confirmed that WGS in food safety surveillance allows accurate detection of genomic relationships between human cases and strains isolated from food samples, including those dispersed over time and geographical locations. Identifying these links can reveal new insights into outbreaks and direct epidemiological investigations to facilitate outbreak management. Complete WGS-based isolate characterization enabled expanding epidemiological insights related to circulating serotypes, virulence genes and antimicrobial resistance across different reservoirs. Moreover, associations between virulence genes and severe disease were determined by incorporating human metadata into the data analysis. Gaps in the surveillance system were identified and suggestions for optimization related to sample centralization, harmonizing isolation methods, and expanding sampling strategies were formulated.

Discussion

This study contributes to developing a representative WGS-based collection of circulating STEC strains and by illustrating its benefits, it aims to incite policymakers to support WGS uptake in food safety surveillance.

Prevalence and Characterization of Shiga Toxin Producing Escherichia coli Isolated from Animal Feed in Croatia

A survey on prevalence and number of Shiga toxin-producing Escherichia (E.) coli (STEC) in animal feed was carried out over a period of nine years in the Republic of Croatia. A total of 1688 feed samples were collected from feed factories and poultry farms. Analysis included two standard procedures: sample enrichment and (a) immunomagnetic separation and plating on two selective media; or (b) plating on two selective media. Confirmation of STEC included morphological examination, biochemical tests, serotyping, and polymerase chain reaction. Morphological and biochemical characterization revealed 629 E. coli strains. Further serological screening method revealed 78 STEC and EPEC serotypes, while only 27 strains were confirmed as STEC with PCR. All positive samples (1.6%) originated from poultry farms and contained combination of virulence genes: eaeA, stx1, and/or stx2. Since the presence of stx (especially stx2) and eae are identified as risk factors for development of severe diseases in humans, results of this survey indicate that avian sources of STEC infections might be one of those “undefined sources” of human illnesses. Further research is necessary for evaluation of risks posed by contaminated feed, poultry, and environment.

Flavorubredoxin, a Candidate Trigger Related to Thrombotic Thrombocytopenic Purpura: Screening of the Complete Genome of a Salmonella enterica Serovar Typhimurium Isolate From an AIDS Case

Thrombotic thrombocytopenic purpura (TTP) is one of the two classic thrombotic microangiopathy (TMA) diseases which could be induced by infections. To the best of our knowledge, this is the first report of an acquired immunodeficiency syndrome (AIDS) patient with acquired TTP induced by infection with Salmonella enterica serovar Typhimurium (hereafter, S. Typhimurium) isolate, S. Typhimurium_zhang, which was confirmed by serology and genetic taxonomy. The literature review identified 17 TMA-related genes encoding the candidate triggers, which were searched in the annotated genome sequence of S. Typhimurium_zhang. Anaerobic nitric oxide reductase flavorubredoxin (FlRd), encoded by norV which is related to another TMA, haemolytic uraemic syndrome (HUS), was found in S. Typhimurium_zhang. Basic local alignment search tool (BLAST) analysis revealed that norV and FlRd in S. Typhimurium_zhang, as well as eight S. Typhimurium type strains, have high identity with HUS-related Escherichia coli O157:H7 strain TW14359. Similar results were obtained from the BLAST analysis of 73 S. enterica isolates for congenital TTP which was also previously reported to be triggered by S. enterica. Phylogenetic analysis and amino acid sequence alignment revealed that FlRd was functional and highly conservative on 69 Enterobacteriaceae, including S. Typimurium_zhang and TW14359. In brief, we found norV in the genome of a S. Typhimurium clinical isolate that induced TTP in an AIDS patient. FlRd, the protein encoded by norV, probably triggered the TTP and was highly conservative, functional, and widespread in S. enterica and Enterobacteriaceae. More in vitro and in vivo studies are required to confirm our findings and determine the underlying mechanism.

Characterization of Shiga Toxin 2a Encoding Bacteriophages Isolated From High-Virulent O145:H25 Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) may cause severe disease mainly due to the ability to produce Shiga toxins (Stx) encoded on bacteriophages. In Norway, more than 30% of the reported cases with STEC O145:H25 develop hemolytic uremic syndrome (HUS), and most cases, with known travel history, acquired the infection domestically. To describe phage characteristics associated with high virulence, we extracted the Stx2a phage sequences from eight clinical Norwegian O145:H25 STEC to conduct in-depth molecular characterization using long and short read sequencing. The Stx2a phages were annotated, characterized, and compared with previously published Stx2a phages isolated from STEC of different serotypes. The Norwegian O145:H25 Stx2a phages showed high sequence identity (>99%) with 100% coverage. The Stx2a phages were located at the integration site yciD, were approximately 45 kbp long, and harbored several virulence-associated genes, in addition to stx2a, such as nanS and nleC. We observed high sequence identity (>98%) and coverage (≥94%) between Norwegian O145:H25 Stx2a phages and publicly available Stx2a phages from O145:H25 and O145:H28 STEC, isolated from HUS cases in the USA and a hemorrhagic diarrhea case from Japan, respectively. However, low similarity was seen when comparing the Norwegian O145:H25 Stx2a phage to Stx2a phages from STEC of other serotypes. In all the Norwegian O145:H25 STEC, we identified a second phage or remnants of a phage (a shadow phage, 61 kbp) inserted at the same integration site as the Stx2a phage. The shadow phage shared similarity with the Stx2a phage, but lacked stx2a and harbored effector genes not present in the Stx2a phage. We identified a conserved Stx2a phage among the Norwegian O145:H25 STEC that shared integration site with a shadow phage in all isolates. Both phage and shadow phage harbored several virulence-associated genes that may contribute to the increased pathogenicity of O145:H25 STEC.

Epidemiology and Characterization of Shiga Toxin-Producing Escherichia Coli of Hemolytic Uremic Syndrome in Argentina

Argentina has one of the highest prevalence in Shiga toxin-producing Escherichia coli (STEC) and the high rate of hemolytic uremic syndrome (HUS) in the world. Though preventive steps such as food safety have been implemented as a way to reduce STEC infections, these have proven to be insufficient. STEC's pathogenesis, virulence factors, relationship with the environment, and emerging strains have been studied in the past few years in the country. Many factors that contribute to the morbidity and mortality of STEC infections include the expression of pathologic genes, alternative characteristics (inhibition of phagocytosis, invasion, cytotoxicity, and bacterial attachment), and host factors (age, immune status, treatments, medical history). However, research studies in combination with epidemiological data suggest trends of the prognosis, with the relationship between and genetic combinations of adherence, Shiga toxin (Stx) genes, and virulence genes, which significantly influence disease outcomes. This review explains the characteristics and epidemiology of STEC in Argentina. All these facts show that the application of molecular subtyping techniques in real-time is essential for detecting and controlling outbreaks. Applying molecular subtyping techniques in hemorrhagic diarrhea can avoid severe consequences caused by progression to HUS, and help the epidemiological analysis of the outbreak. 

The emerging importance of Shiga toxin-producing Escherichia coli other than serogroup O157 in England

Introduction

Shiga toxin-producing Escherichia coli (STEC) can cause severe disease and large outbreaks. In England, the incidence and clinical significance of STEC serogroups other than O157 (non-O157) is unknown due to a testing bias for detection of STEC O157. Since 2013, the implementation of PCR to detect all STEC serogroups by an increasing number of diagnostic laboratories has led to an increase in the detection of non-O157 STEC.

Hypothesis/Gap statement

Due to a bias in testing methodologies to select for STEC serogroup O157 in frontline diagnostic laboratories in most countries, very little surveillance data have been previously generated on non-O157 STEC.

Aim

Five years (2014–2018) of STEC national surveillance data were extracted and descriptive analysis undertaken to assess disease severity of non-O157 STEC strains.

Methods

Data from 1 January 2014 to 31 December 2018 were extracted from the National Enhanced Surveillance System for STEC and analysed.

Results

The implementation of Gastrointestinal Polymerase Chain Reaction (GI-PCR) has resulted in a four-fold increase in the detection of non-O157 STEC cases between 2014 and 2018. There were 2579 cases infected with 97 different non-O157 serogroups. The gender distribution was similar amongst STEC O157 and non-O157 STEC cases with 57 and 56 % of cases being female respectively, but a significantly higher proportion of cases (P <0.001) under 5 years of age was observed among STEC O157 (22 %) cases compared to non-O157 STEC (14 %). The most common non-O157 serogroups were O26 (16 %), O146 (11 %), O91 (10 %), O128 (7 %), O103 (5 %) and O117 (3 %). Overall, rates of bloody diarrhoea were highest in O26 (44 %) and O103 (48 %) cases and lowest in STEC O117 cases (17 %). Strains harbouring Shiga toxin stx1a caused the highest proportion of diarrhoea (93 %) and caused the same level of bloody diarrhoea as stx2a (39 %). However, stx2a caused the highest proportion of vomiting (46 %), hospitalisation (49 %) and considerably more HUS (29 %) than other stx profiles.

Conclusion

The implementation of PCR targeting stx at diagnostic laboratories has shown that non-O157 STEC, most notably STEC O26, are an emerging risk to public health.

Association between Shiga Toxin-Producing Escherichia coli O157:H7 stx Gene Subtype and Disease Severity, England, 2009-2019

Signs and symptoms of Shiga toxin–producing Escherichia coli (STEC) serogroup O157:H7 infection range from mild gastrointestinal to bloody diarrhea and hemolytic uremic syndrome (HUS). We assessed the association between Shiga toxin gene (stx) subtype and disease severity for »3,000 patients with STEC O157:H7 in England during 2009–2019. Odds of bloody diarrhea, HUS, or both, were significantly higher for patients infected with STEC O157:H7 possessing stx2a only or stx2a combined with other stx subtypes. Odds of severe signs/symptoms were significantly higher for isolates encoding stx2a only and belonging to sublineage Ic and lineage I/II than for those encoding stx2a only and belonging to sublineage IIb, indicating that stx2a is not the only driver causing HUS. Strains of STEC O157:H7 that had stx1a were also significantly more associated with severe disease than strains with stx2c only. This finding confounds public health risk assessment algorithms based on detection of stx2 as a predictor of severe disease.

Pathogenic potential assessment of the Shiga toxin-producing Escherichia coli by a source attribution-considered machine learning model

Instead of conventional serotyping and virulence gene combination methods, methods have been developed to evaluate the pathogenic potential of newly emerging pathogens. Among them, the machine learning (ML)-based method using whole-genome sequencing (WGS) data are getting attention because of the recent advances in ML algorithms and sequencing technologies. Here, we developed various ML models to predict the pathogenicity of Shiga toxin-producing Escherichia coli (STEC) isolates using their WGS data. The input dataset for the ML models was generated using distinct gene repertoires from positive (pathogenic) and negative (nonpathogenic) control groups in which each STEC isolate was designated based on the source attribution, the relative risk potential of the isolation sources. Among the various ML models examined, a model using the support vector machine (SVM) algorithm, the SVM model, discriminated between the two control groups most accurately. The SVM model successfully predicted the pathogenicity of the isolates from the major sources of STEC outbreaks, the isolates with the history of outbreaks, and the isolates that cannot be assessed by conventional methods. Furthermore, the SVM model effectively differentiated the pathogenic potentials of the isolates at a finer resolution. Permutation importance analyses of the input dataset further revealed the genes important for the estimation, proposing the genes potentially essential for the pathogenicity of STEC. Altogether, these results suggest that the SVM model is a more reliable and broadly applicable method to evaluate the pathogenic potential of STEC isolates compared with conventional methods.

A Targeted Sequencing Assay for Serotyping Escherichia coli Using AgriSeq Technology

The gold standard method for serotyping Escherichia coli has relied on antisera-based typing of the O- and H-antigens, which is labor intensive and often unreliable. In the post-genomic era, sequence-based assays are potentially faster to provide results, could combine O-serogrouping and H-typing in a single test, and could simultaneously screen for the presence of other genetic markers of interest such as virulence factors. Whole genome sequencing is one approach; however, this method has limited multiplexing capabilities, and only a small fraction of the sequence is informative for subtyping or identifying virulence potential. A targeted, sequence-based assay and accompanying software for data analysis would be a great improvement over the currently available methods for serotyping. The purpose of this study was to develop a high-throughput, molecular method for serotyping E. coli by sequencing the genes that are required for production of O- and H-antigens, as well as to develop software for data analysis and serotype identification. To expand the utility of the assay, targets for the virulence factors, Shiga toxins (stx₁, and stx₂) and intimin (eae) were included. To validate the assay, genomic DNA was extracted from O-serogroup and H-type standard strains and from Shiga toxin-producing E. coli, the targeted regions were amplified, and then sequencing libraries were prepared from the amplified products followed by sequencing of the libraries on the Ion S5™ sequencer. The resulting sequence files were analyzed via the SeroType Caller™ software for identification of O-serogroup, H-type, and presence of stx₁, stx₂, and eae. We successfully identified 169 O-serogroups and 41 H-types. The assay also routinely detected the presence of stx_1a,c,d (3 of 3 strains), stx_2c−e,g (8 of 8 strains), stx_2f (1 strain), and eae (6 of 6 strains). Taken together, the high-throughput, sequence-based method presented here is a reliable alternative to antisera-based serotyping methods for E. coli.

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

Effects of antimicrobials on Shiga toxin production in high-virulent Shiga toxin-producing Escherichia coli

PURPOSE

Antimicrobial treatment of Shiga toxin-producing Escherichia coli (STEC) infections is controversial because antimicrobials may stimulate Shiga toxin (Stx) production, and thereby increase the risk of developing haemolytic uremic syndrome (HUS). Previous in vitro studies have shown this mainly in infections caused by STEC serotype O157:H7. The aim of this study was to investigate induction of Stx transcription and production in different serotypes of STEC isolated from severely ill patients, following their exposure in vitro to six different classes of antimicrobials.

METHODS

We investigated Stx transcription and production in 12 high-virulent STEC strains, all carrying the stx2a gene, of six different serotypes following their exposure to six classes of antimicrobials. Liquid cultures of the STEC strains were incubated with sub-inhibitory concentrations of the antimicrobials. We used reverse-transcription quantitative PCR to measure the relative expression of Stx2a mRNA and an enzyme-linked immunosorbent assay to quantify Stx production.

RESULTS

In general the antibiotics tested showed only minor effects on transcriptional levels of Stx2a. Ciprofloxacin caused an increase of Stx production in all but two strains, while gentamicin, meropenem and azithromycin did not induce Stx production in any of the STEC strains examined. STEC O104:H4 was the serotype that in greatest extent responded to antimicrobial exposure with an increase of stx2a transcription and Stx production.

CONCLUSION

Gentamicin, meropenem and azithromycin exposure did not result in elevated Stx production. We recommend that this finding is investigated further in the search for candidates for future antimicrobial treatment of STEC.

Occurrence, Molecular Characteristics, and Antimicrobial Resistance of Escherichia coli O157 in Cattle, Beef, and Humans in Bishoftu Town, Central Ethiopia

Escherichia coli O157 is a Shiga toxin-producing E. coli causing disease in humans. Cattle are the primary reservoir of the pathogen. Information regarding the contribution of cattle to diarrheal illnesses in humans through consumption of contaminated beef is scarce in Ethiopia. We collected samples from 240 cattle, 127 beef, and 216 diarrheic patients in Bishoftu town in Ethiopia to assess the occurrence and determine the virulence genes, genetic relatedness, and antimicrobial resistance of E. coli O157. E. coli O157 was detected in 7.1% of the rectal content samples from cattle in slaughterhouses, in 6.3% (n = 127) of the beef samples, and in 2.8% of the diarrheic patients' stool samples. All isolates were positive for eae gene, 24 (77%) of them were positive for stx2 gene (21 stx2c and 3 stx2a), whereas stx1 gene was not detected. Molecular typing grouped the isolates into eight pulsed-field gel electrophoresis pulsotypes with three pulsotypes containing isolates from all three sources, one pulsotype containing one isolate from human origin and one isolate from beef. The remaining four pulsotypes contained isolates unique either to beef or to humans. With the exception of 1 multidrug-resistant isolate from beef, which was resistant to 8 antimicrobial drugs, the remaining 30 isolates were susceptible to the 14 antimicrobials tested. In conclusion, the finding of genetically similar isolates in cattle, beef, and humans may indicate a potential transmission of E. coli O157 from cattle to humans through beef. However, more robust studies are required to confirm this epidemiological link.

Mapping of control measures to prevent secondary transmission of STEC infections in Europe during 2016 and revision of the national guidelines in Norway

In 2016, we reviewed preventive control measures for secondary transmission of Shiga-toxin producing Escherichia coli (STEC) in humans in European Union (EU)/European Free Trade Association (EEA) countries to inform the revision of the respective Norwegian guidelines which at that time did not accommodate for the varying pathogenic potential of STEC. We interviewed public health experts from EU/EEA institutes, using a semi-structured questionnaire. We revised the Norwegian guidelines using a risk-based approach informed by the new scientific evidence on risk factors for HUS and the survey results. All 13 (42%) participating countries tested STEC for Shiga toxin (stx) 1, stx2 and eae (encoding intimin). Five countries differentiated their control measures based on clinical and/or microbiological case characteristics, but only Denmark based their measures on routinely conducted stx subtyping. In all countries, but Norway, clearance was obtained with ⩽3 negative STEC specimens. After this review, Norway revised the STEC guidelines and recommended only follow-up of cases infected with high-virulent STEC (determined by microbiological and clinical information); clearance is obtained with three negative specimens. Implementation of the revised Norwegian guidelines will lead to a decrease of STEC cases needing follow-up and clearance, and will reduce the burden of unnecessary public health measures and the socioeconomic impact on cases. This review of guidelines could assist other countries in adapting their STEC control measures.

Implementation of multiplex PCR diagnostics for gastrointestinal pathogens linked to increase of notified Shiga toxin-producing Escherichia coli cases in Norway, 2007-2017

The aim of this study was to investigate implementation of multiplex PCR assays (broad screening PCR) on the distribution and characteristics of notified Shiga toxin-producing Escherichia coli (STEC) cases in Norway, 2007-2017. We described STEC cases notified to the Norwegian Surveillance System for Communicable Diseases (MSIS), 2007-2017 and categorised cases as high-virulent, low-virulent or unclassifiable STEC infections based on guidelines for follow-up of STEC cases. We conducted descriptive analysis and time series analysis allowing for trends and seasonality, and calculated adjusted incidence rate ratios (aIRR) using negative binomial regression for laboratories with and without broad screening PCR. A total of 1458 STEC cases were notified to MSIS (2007-2017), median age 21 years, 51% female. Cases were categorised as having 475 (33%) high-virulent, 652 (45%) low-virulent, and 331 (23%) unclassifiable STEC infections. We observed a higher increasing monthly trend in cases (aIRR = 1.020; 95% CI 1.016-1.024) notified from laboratories with broad screening PCR (n = 4) compared to laboratories (n = 17) without (aIRR = 1.011; 95% CI 1.007-1.014). Notification of low-virulent STEC infections increased from laboratories with broad screening PCR. The increase in notified STEC cases was prominent in cases categorised with a low-virulent STEC infection and largely attributable to unselective screening methods. We recommend NIPH to maintain differentiated control measures for STEC cases to avoid follow-up of low-virulent STEC infections. We recommend microbiological laboratories in Norway to consider a more cost-effective broad screening PCR strategy that enables differentiation of high-virulent STEC infections.

The Significance of Mesophilic Aeromonas spp. in Minimally Processed Ready-to-Eat Seafood

Minimally processed and ready-to-eat (RTE) seafood products are gaining popularity because of their availability in retail stores and the consumers' perception of convenience. Products that are subjected to mild processing and products that do not require additional heating prior to consumption are eaten by an increasing proportion of the population, including people that are more susceptible to foodborne disease. Worldwide, seafood is an important source of foodborne outbreaks, but the exact burden is not known. The increased interest in seafood products for raw consumption introduces new food safety issues that must be addressed by all actors in the food chain. Bacteria belonging to genus Aeromonas are ubiquitous in marine environments, and Aeromonas spp. has held the title "emerging foodborne pathogen" for more than a decade. Given its high prevalence in seafood and in vegetables included in many RTE seafood meals, the significance of Aeromonas as a potential foodborne pathogen and a food spoilage organism increases. Some Aeromonas spp. can grow relatively uninhibited in food during refrigeration under a broad range of pH and NaCl concentrations, and in various packaging atmospheres. Strains of several Aeromonas species have shown spoilage potential by the production of spoilage associated metabolites in various seafood products, but the knowledge on spoilage in cold water fish species is scarce. The question about the significance of Aeromonas spp. in RTE seafood products is challenged by the limited knowledge on how to identify the truly virulent strains. The limited information on clinically relevant strains is partly due to few registered outbreaks, and to the disputed role as a true foodborne pathogen. However, it is likely that illness caused by Aeromonas might go on undetected due to unreported cases and a lack of adequate identification schemes. A rather confusing taxonomy and inadequate biochemical tests for species identification has led to a biased focus towards some Aeromonas species. Over the last ten years, several housekeeping genes has replaced the 16S rRNA gene as suitable genetic markers for phylogenetic analysis. The result is a more clear and robust taxonomy and updated knowledge on the currently circulating environmental strains. Nevertheless, more knowledge on which factors that contribute to virulence and how to control the potential pathogenic strains of Aeromonas in perishable RTE seafood products are needed.

Shiga toxin-producing Escherichia coli in wild ungulates

Shiga toxin-producing Escherichia coli (STEC) are zoonotic pathogens that live in the gastrointestinal tract of wildlife and cattle without causing disease. In humans, their colonization and infection lead to life-threatening disease. We investigated the occurrence of STEC in wild ungulates (wild boar, red deer and roe deer) inhabiting areas differently impacted by anthropogenic activities. STEC were detected in 9% (n = 6) of the samples and were recovered from the three species: 1 of wild boar, 4 of red deer and 1 of roe deer. All the isolates (n = 7) were non-O157 STEC encoding stx1 (n = 2; 29%) and/or stx2 genes (n = 6; 86%). O27:H30 was the most frequent serotype identified, followed by O146:H21 and O146:H28. Two STEC were O-untypable: ONT:H28 and ONT:H52. The phylo-groups identified were B1 (n = 3), E (n = 3) and F (n = 1). All the isolates recovered were susceptible to the different classes of antibiotics tested, although resistance genes were found in two strains. Apart from stx, all STEC encode many virulence factors (VF), particularly adhesins and/or other toxins. A strain with 13 VF collected from roe deer has a high enterohemorrhagic risk due to the presence of intimin, hemolysin and protease effectors genes. Enterohemorrhagic E. coli (EHEC) are implicated in the major cases of human infection and mortality, highlighting the zoonotic potential of wildlife-associated STEC. Wild ungulates are reservoirs of STEC potentially pathogenic to humans. Therefore, following the One Health concept, it is crucial to establish worldwide local monitoring programs that will benefit human, animal and environmental health.

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

Shiga toxin-producing Escherichia coli (STEC) comprise a large, highly diverse group of strains. Since the emergence of STEC serotype O157:H7 as an important foodborne pathogen, serotype data have been used for identifying STEC strains, and this use continued as other serotypes were implicated in human infections. An estimated 470 STEC serotypes have been identified, which can produce one or more of the 12 known Shiga toxin (Stx) subtypes. The number of STEC serotypes that cause human illness varies but is probably higher than 100. However, many STEC virulence genes are mobile and can be lost or transferred to other bacteria; therefore, STEC strains that have the same serotype may not carry the same virulence genes or pose the same risk. Although serotype information is useful in outbreak investigations and surveillance studies, it is not a reliable means of assessing the human health risk posed by a particular STEC serotype. To contribute to the development of a set of criteria that would more reliably support hazard identification, this review considered each of the factors contributing to a negative human health outcome: mild diarrhea, bloody diarrhea, and hemolytic uremic syndrome (HUS). STEC pathogenesis involves entry into the human gut (often via ingestion), attachment to the intestinal epithelial cells, and elaboration of Stx. Production of Stx, which disrupts normal cellular functions and causes cell damage, alone without adherence of bacterial cells to gut epithelial cells is insufficient to cause severe illness. The principal adherence factor in STEC is the intimin protein coded by the eae gene. The aggregative adherence fimbriae adhesins regulated by the aggR gene of enteroaggregative E. coli strains are also effective adherence factors. The stx_2a gene is most often present in locus of enterocyte effacement ( eae)-positive STEC strains and has consistently been associated with HUS. The stx_2a gene has also been found in eae-negative, aggR-positive STEC that have caused HUS. HUS cases where other stx gene subtypes were identified indicate that other factors such as host susceptibility and the genetic cocktail of virulence genes in individual isolates may affect their association with severe diseases.

Implications of stx loss for clinical diagnostics of Shiga toxin-producing Escherichia coli

The dynamics related to the loss of stx genes from Shiga toxin-producing Escherichia coli remain unclear. Current diagnostic procedures have shortcomings in the detection and identification of STEC. This is partly owing to the fact that stx genes may be lost during an infection or in the laboratory. The aim of the present study was to provide new insight into in vivo and in vitro stx loss in order to improve diagnostic procedures. Results from the study support the theory that loss of stx is a strain-related phenomenon and not induced by patient factors. It was observed that one strain could lose stx both in vivo and in vitro. Whole genome comparison of stx-positive and stx-negative isolates from the same patient revealed that different genomic rearrangements, such as complete or partial loss of the parent prophage, may be factors in the loss of stx. Of diagnostic interest, it was shown that patients can be co-infected with different E. coli pathotypes. Therefore, identification of eae-positive, but stx-negative isolates should not be interpreted as "Shiga toxin-lost" E. coli without further testing. Growth and recovery of STEC were supported by different selective agar media for different strains, arguing for inclusion of several media in STEC diagnostics.

Risk determinants for the development of typical haemolytic uremic syndrome in Belgium and proposition of a new virulence typing algorithm for Shiga toxin-producing Escherichia coli

In Belgium, it is mandatory to report Shiga toxin-producing Escherichia coli (STEC) infections to the health inspection authorities. To facilitate the decision making regarding infection control measures, information about the risk factors for the development of the haemolytic uremic syndrome (HUS) can be helpful. We performed statistical analyses on a dataset of 411 Belgian STEC strains. Demographic and clinical patient characteristics as well as phenotypical and genotypical STEC strain characteristics were taken into account. Multivariate logistic regression models indicated that age categories ⩽5, 6-12 and ⩾75; the stx2 gene; and the eae gene were significant HUS development risk determinants. The stx2a subtype had the highest risk (OR 29.6, 95% CI 7.0-125.1), while all stx1 subtypes encompassed a significant lower risk (OR 0.3, 95% CI 0.1-0.5). Presence of the stx1 gene without stx2 encompassed a lower risk than the combined presence of stx1 and stx2, or stx2 solely. Based on these results, we propose a new virulence typing algorithm that will enable the National Reference Centre to provide the physicians and health inspection authorities with a risk classification for the development of HUS. We believe this will contribute to a more efficient STEC infection control management in Belgium.

Shiga Toxin-Producing Escherichia coli Infection in Jönköping County, Sweden: Occurrence and Molecular Characteristics in Correlation With Clinical Symptoms and Duration of stx Shedding

Shiga toxin-producing Escherichia coli (STEC) cause bloody diarrhea (BD), hemorrhagic colitis (HC), and even hemolytic uremic syndrome (HUS). In Nordic countries, STEC are widely spread and usually associated with gastrointestinal symptoms and HUS. The objective of this study was to investigate the occurrence of STEC in Swedish patients over 10 years of age from 2003 through 2015, and to analyze the correlation of critical STEC virulence factors with clinical symptoms and duration of stx shedding. Diarrheal stool samples were screened for presence of stx by real-time PCR. All STEC isolates were characterized by DNA microarray assay and PCR to determine serogenotypes, stx subtypes, and presence of intimin gene eae and enterohaemolysin gene ehxA. Multilocus sequencing typing (MLST) was used to assess phylogenetic relationships. Clinical features were collected and analyzed using data from the routine infection control measures in the county. A total of 14,550 samples were enrolled in this 12-years period study, and 175 (1.2%) stools were stx positive by real-time PCR. The overall incidence of STEC infection was 4.9 cases per 100,000 person-years during the project period. Seventy-five isolates, with one isolate per sample were recovered, among which 43 were from non-bloody stools, 32 from BD, and 3 out of the 75 STEC positive patients developed HUS. The presence of stx2 in both stools and isolates were associated with BD (p = 0.008, p = 0.05), and the presence of eae in isolates was related to BD (p = 0.008). The predominant serogenotypes associated with BD were O157:H7, O26:H11, O121:H19, and O103:H2. Isolates from HUS were O104:H4 and O98: H21 serotypes. Phylogenetic analysis revealed our strains were highly diverse, and showed close relatedness to HUS-associated STEC collection strains. In conclusion, the presence of stx2 in stool was related to BD already at the initial diagnostic procedure, thus could be used as risk predictor at an early stage. STEC isolates with stx2 and eae were significantly associated with BD. The predominant serotypes associated with BD were O157:H7, O26:H11, O121:H19, and O103:H2. Nevertheless, the pathogenic potential of other serotypes and genotypes should not be neglected.