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

From wheat grain to flour: a review of potential sources of enteric pathogen contamination in wheat milled products

The number of food safety issues linked to wheat milled products have increased in the past decade. These incidents were mainly caused by the contamination of wheat-based products by enteric pathogens. This manuscript is the first of a two-part review on the status of the food safety of wheat-based products. This manuscript focused on reviewing the available information on the potential pre-harvest and post-harvest sources of microbial contamination, and potential foodborne pathogens present in wheat-based products. Potential pre-harvest sources of microbial contamination in wheat included animal activity, water, soil, and manure. Improper grain storage practices, pest activity, and improperly cleaned and sanitized equipment are potential sources of post-harvest microbial contamination for wheat-based foods. Raw wheat flour products and flour-based products are potentially contaminated with enteric pathogens such as Shiga toxin-producing E. coli (STECs), and Salmonella at low concentrations. Wheat grains and their derived products (i.e., flours) are potential vehicles for foodborne illness in humans due to the presence of enteric pathogens. A more holistic approach is needed for assuring the food safety of wheat-based products in the farm-to-table continuum. Future developments in the wheat supply chain should also be aimed at addressing this emerging food safety threat.

Phage Biocontrol Effectively Reduces Contamination of Wheat with Shiga Toxin-producing Escherichia coli O121 and O26 Without Adverse Effects on Flour Quality

Contamination of wheat flours with Shiga toxin-producing E. coli (STEC) is a concern for the milling industry. Milling-specific interventions are needed to address this food safety hazard. The objectives for this study were to determine the efficacy of bacteriophage treatment in reducing wheat STEC contamination during tempering, and assess its effects on flour milling and baking quality. Bacteriophage solutions were prepared by mixing sterile water with the bacteriophage treatment at the following levels: 1 × 106 (0.1%), 2.5 × 106 (0.25%), 5 × 106 (0.5%), 1 × 107 (1.0%), and 1 × 108 (10%) PFU/g wheat dosage. Sterile water (0%) was used as the control. Predried wheat grains were inoculated with STEC (O121 and O26) at 5.0 and 6.0 log CFU/g to restore its original moisture content followed by resting for 24 h. Inoculated grains were then tempered (16% moisture, 24 h) using the prepared bacteriophage solutions. Grains were sampled at 0.5, 1, 2, 6, 12, 18, and 24 h during tempering to determine STEC concentration. The effects of the phage solutions on the flour milling and baking quality were also tested. Tempering time, bacteriophage dose, and their interaction had significant effects on phage efficacy (P < 0.05), with better reductions observed at longer tempering times and higher bacteriophage doses. The use of phage solutions reduced (P < 0.05) wheat STEC concentration after tempering, with the 10% treatment (3.2 logs) achieving ahigher reduction than the 1% (2.4 logs) treatment under similar phage preparation. Phage tempering (including at the highest concentration examined, i.e., 10%) produced wheat flours with comparable quality to the control. Phage-treated wheat flour resulted in breads with finer crumb structure, and comparable texture compared to the control. Phage tempering is a viable intervention for wheat milling as it reduced STEC loads of wheat with no detrimental effects to flour milling and baking quality.

Shiga toxin-producing Escherichia coli (STEC) and atypical enteropathogenic E. coli (aEPEC) in Swedish retail wheat flour

Wheat flour has been identified as the source of multiple outbreaks of gastrointestinal disease caused by shiga toxin-producing Escherichia coli (STEC). We have investigated the presence and genomic characteristics of STEC and related atypical enteropathogenic E. coli (aEPEC) in 200 bags of Swedish-produced retail wheat flour, representing 87 products and 25 brands. Samples were enriched in modified tryptone soya broth (mTSB) and screened with real-time PCR targeting stx₁, stx₂ and eae, and the serogroups O157, O121 and O26. Isolation was performed by immunomagnetic separation (IMS) for suspected STEC/aEPEC O157, O121 and O26, and by screening pools of colonies for other STEC. Real-time PCR after enrichment revealed 12 % of samples to be positive for shiga toxin genes (stx₁ and/or stx₂) and 11 % to be positive for intimin (eae). Organic production, small-scale production or whole grain did not significantly influence shiga toxin gene presence or absence in a generalized linear mixed model analysis. Eight isolates of STEC were recovered, all of which were intimin-negative. Multiple serotype/sequence type/shiga toxin subtype combinations that have also been found in flour samples in other European countries were recovered. Most STEC types recovered were associated with sporadic cases of STEC among humans in Sweden, but no types known to have caused outbreaks or severe cases of disease (i.e. haemolytic uraemic syndrome) were found. The most common finding was O187:H28 ST200 with stx_2g, with possible links to cervid hosts. Wildlife associated with crop damage is a plausible explanation for at least some of the surprisingly high frequency of STEC in wheat flour.

Variations in the motility and biofilm formation abilities of Escherichia coli O157:H7 during noodle processing

Motility and biofilm formation help to protect bacteria from host immune responses and facilitate tolerance of environmental stimuli to improve their adaptability. However, few reports have investigated the adaptability of bacteria that live in food substrates undergoing food processing-induced stress. In this study, variations in the surface morphology, bacterial count, motility, and biofilm formation abilities of Escherichia coli O157:H7 NCTC12900 were investigated during noodle processing, including the kneading, squeezing, resting, and sheeting phases. The results showed that bacterial surface morphology, count, and motility were impaired in the squeezing phase, whereas biofilm biomass continuously increased across all processing phases. Twenty-one genes and sRNAs were measured using RT-qPCR to reveal the mechanisms underlying these changes. Of these, the genes adrA, csrA, flgM, flhD, fliM, ydaM, and the sRNA McaS were significantly upregulated, whereas the genes fliA, fliG, and the sRNAs CsrC, DsrA, GcvB, and OxyS were evidently repressed. According to the correlation matrix results based on the reference gene adrA, we found that csrA, GcvB, McaS, and OxyS were the most relevant genes and sRNAs for biofilm formation and motility. For each of them, their overexpressions was found to inhibit bacterial motility and biofilm formation to varying degrees during noodle processing. Among these, 12900/pcsrA had the highest inhibitory potential against motility, yielding a minimum of 11.2 mm motility diameter in the resting phase. Furthermore, 12900/pOxyS showed the most significant inhibitory effect against biofilm formation, yielding a minimum biofilm formation value of 5% of that exhibited the wild strain in the sheeting phase. Therefore, we prospect to find an effective and feasible novel approach to weaken bacterial survival during food processing by regulating the genes or sRNAs related to motility and biofilm formation.

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.

Molecular characterization and phylogeny of Shiga toxin-producing Escherichia coli derived from cattle farm

Shiga toxin-producing Escherichia coli (STEC) is an important food-borne pathogen, which can cause diseases such as diarrhea, hemorrhagic enteritis, and hemolytic uremic syndrome in humans. Twelve STEC isolates were collected from beeves and feces of commercial animals in China between 2019 and 2020 for this study. In addition to the determination of serotype and Shiga toxin subtype, whole-genome sequencing (WGS) was used for determining phylogenetic relationships, antimicrobial resistance (AMR), virulence genes, and sequence type (ST) of isolates. A total of 27 AMR genes were detected, and each STEC isolate carried more than 10 AMR genes. Eight STEC isolates from ground beef and four STEC isolated from feces were screened. A total of seven serotypes were identified, and one isolate ONT:H10 was undetermined by SeroTypeFinder. Three O157:H7 strains were confirmed and the remaining five serogroups were confirmed as O26:H11, O81:H31, O105:H8, O178:H19, and O136:H12. The phylogenetic analysis showed that STEC isolates of the same serotype or ST were clustered together based on cgMLST. The comparison of the genomes of 157 STEC reference isolates worldwide with our local STEC isolates showed that STEC isolates screened in China represented various collections and could not form a separate cluster but were interspersed among the STEC reference collection, which suggested that several STEC isolates shared a common ancestor irrespective of STEC serotype isolates. cgMLST revealed that isolates of the same O serotype clustered irrespective of their H type. Further investigation is required to determine the pathogenic potential of other serotypes of STEC, particularly in regard to these rare serotypes.

Shiga toxin-producing Escherichia coli clonal complex 32, including serotype O145:H28, in the UK and Ireland

Introduction. Shiga toxin-producing Escherichia coli (STEC) O157:H7 has been the most clinically significant STEC serotype in the UK for over four decades. Over the last 10 years we have observed a decrease in STEC O157:H7 and an increase in non-O157 STEC serotypes, such as O145:H28.Gap Statement. Little is known about the microbiology and epidemiology of STEC belonging to CC32 (including O145:H28) in the UK. The aim of this study was to integrate genomic data with patient information to gain a better understanding of the virulence, disease severity, epidemic risk assessment and population structure of this clinically significant clonal complex.Methodology. Isolates of E. coli belonging to CC32 (n=309) in the archives of public health agencies in the UK and Ireland were whole-genome-sequenced, virulence-profiled and integrated with enhanced surveillance questionnaire (ESQ) data, including exposures and disease severity.Results. Overall, diagnoses of STEC belonging to CC32 (290/309, 94 %) in the UK have increased every year since 2014. Most cases were female (61 %), and the highest proportion of cases belonged to the 0-4 age group (53/211,25 %). The frequency of symptoms of diarrhoea (92 %), abdominal pain (84 %), blood in stool (71 %) and nausea (51 %) was similar to that reported in cases of STEC O157:H7, although cases of STEC CC32 were more frequently admitted to hospital (STEC CC32 48 % vs O157:H7  34 %) and/or developed haemolytic uraemic syndrome (HUS) (STEC CC32 9 % vs O157:H7 4 %).The majority of STEC isolates (268/290, 92 %) had the stx2a/eae virulence gene combination, most commonly associated with progression to STEC HUS. There was evidence of person-to-person transmission and small, temporally related, geographically dispersed outbreaks, characteristic of foodborne outbreaks linked to nationally distributed products.Conclusion. We recommend more widespread use of polymerase chain reaction (PCR) for the detection of all STEC serogroups, the development of consistent strategies for the follow-up testing of PCR-positive faecal specimens, the implementation of more comprehensive and standardized collection of epidemiological data, and routine sharing of sequencing data between public health agencies worldwide.

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.