Shiga Toxin Producing Escherichia coli

A bacterial toxin co-opts caspase-3 to disable active gasdermin D and limit macrophage pyroptosis

During infections, host cells are exposed to pathogen-associated molecular patterns (PAMPs) and virulence factors that stimulate multiple signaling pathways that interact additively, synergistically, or antagonistically. The net effect of such higher-order interactions is a vital determinant of the outcome of host-pathogen interactions. Here, we demonstrate one such complex interplay between bacterial exotoxin- and PAMP-induced innate immune pathways. We show that two caspases activated during enterohemorrhagic Escherichia coli (EHEC) infection by lipopolysaccharide (LPS) and Shiga toxin (Stx) interact in a functionally antagonistic manner; cytosolic LPS-activated caspase-11 cleaves full-length gasdermin D (GSDMD), generating an active pore-forming N-terminal fragment (NT-GSDMD); subsequently, caspase-3 activated by EHEC Stx cleaves the caspase-11-generated NT-GSDMD to render it nonfunctional, thereby inhibiting pyroptosis and interleukin-1β maturation. Bacteria typically subvert inflammasomes by targeting upstream components such as NLR sensors or full-length GSDMD but not active NT-GSDMD. Thus, our findings uncover a distinct immune evasion strategy where a bacterial toxin disables active NT-GSDMD by co-opting caspase-3.

Shiga Toxin-Producing Escherichia coli Testing in New York 2011-2022 Reveals Increase in Non-O157 Identifications

Shiga toxin-producing Escherichia coli (STEC) are an important cause of bacterial enteric infection. STEC strains cause serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic uremic syndrome. They have the potential to impact public health due to diagnostic challenges of identifying non-O157 strains in the clinical laboratory. The Wadsworth Center (WC), the public health laboratory of the New York State Department of Health, has isolated and identified non-O157 STEC for decades. A shift from initially available enzyme immunoassay testing to culture-independent diagnostic tests (CIDTs) has increased the uptake of testing at clinical microbiology laboratories. This testing change has resulted in an increased number of specimen submissions to WC. During a 12-year period between 2011 and 2022, WC received 5037 broths and/or stool specimens for STEC confirmation from clinical microbiology laboratories. Of these, 3992 were positive for Shiga toxin genes (stx1 and/or stx2) by real-time PCR. Furthermore, culture methods were utilized to isolate, identify, and characterize 2925 STEC from these primary specimens. Notably, WC observed a >200% increase in the number of STEC specimens received in 2021-2022 compared with 2011-2012 and an 18% increase in the number of non-O157 STEC identified using the same methodologies. During the past decade, the WC testing algorithm has been updated to manage the increase in specimens received, while also navigating the novel COVID-19 pandemic, which took priority over other testing for a period of time. This report summarizes updated methods for confirmation, surveillance, and outbreak detection of STEC and describes findings that may be related to our algorithm updates and the increased use of CIDTs, which is starting to elucidate the true incidence of non-O157 STEC.

Detection and characterization of circulating microvesicles containing Shiga toxin type 2 in a rat model of Hemolytic Uremic Syndrome

Shiga toxin producing Escherichia coli (STEC) are foodborne pathogens that release Shiga toxin (Stx), virulence factor responsible for the development of Hemolytic Uremic Syndrome (HUS). Stx causes endothelial cell damage, which leads to platelets deposition and thrombi formation within the microvasculature. It has been described that Stx activates blood cells and induces the shedding of proinflammatory and prothrombotic microvesicles (MVs) containing the toxin. In this sense, it has been postulated that MVs containing Stx2 (MVs-Stx2+) can contribute to the physiopathology of HUS, allowing Stx2 to reach the target organs while evading the immune system. In this work, we propose that circulating MVs-Stx2+ can be a potential biomarker for the diagnosis and prognosis of STEC infections and HUS progression. We developed a rat HUS model by the intraperitoneal injection of a sublethal dose of Stx2 and observed: decrease in body weight, increase of creatinine and urea levels, decrease of creatinine clearance and histological renal damages. After characterization of renal damages, we investigated circulating total MVs and MVs-Stx2+ by flow cytometry at different times after Stx2 injection. Additionally, we evaluated the correlation of biochemical parameters such as creatinine and urea in plasma with MVs-Stx2+. As a result, we found a significant circulation of MVs-Stx2+ at 72 and 96 h after Stx2 injection, nevertheless no correlation with creatinine and urea plasma levels were detected. Our results suggest that MVs-Stx2+ may be an additional biomarker for the characterization and diagnosis of HUS progression. A further analysis is required in order to validate MVs-Stx2+ as biomarker of the disease.

Genetic Characterization of Intimin Gene (eae) in Clinical Shiga Toxin-Producing Escherichia coli Strains from Pediatric Patients in Finland

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections cause outbreaks of severe disease in children ranging from bloody diarrhea to hemolytic uremic syndrome (HUS). The adherent factor intimin, encoded by eae, can facilitate the colonization process of strains and is frequently associated with severe disease. The purpose of this study was to examine and analyze the prevalence and polymorphisms of eae in clinical STEC strains from pediatric patients under 17 years old with and without HUS, and to assess the pathogenic risk of different eae subtypes. We studied 240 STEC strains isolated from pediatric patients in Finland with whole genome sequencing. The gene eae was present in 209 (87.1%) strains, among which 49 (23.4%) were from patients with HUS, and 160 (76.6%) were from patients without HUS. O157:H7 (126, 60.3%) was the most predominant serotype among eae-positive STEC strains. Twenty-three different eae genotypes were identified, which were categorized into five eae subtypes, i.e., γ1, β3, ε1, θ and ζ3. The subtype eae-γ1 was significantly overrepresented in strains from patients aged 5-17 years, while β3 and ε1 were more commonly found in strains from patients under 5 years. All O157:H7 strains carried eae-γ1; among non-O157 strains, strains of each serotype harbored one eae subtype. No association was observed between the presence of eae/its subtypes and HUS. However, the combination of eae-γ1+stx2a was significantly associated with HUS. In conclusion, this study demonstrated a high occurrence and genetic variety of eae in clinical STEC from pediatric patients under 17 years old in Finland, and that eae is not essential for STEC-associated HUS. However, the combination of certain eae subtypes with stx subtypes, i.e., eae-γ1+stx2a, may be used as risk predictors for the development of severe disease in children.

Enteropathogenic Escherichia coli is a predominant pathotype in healthy pigs in Hubei Province of China

AIM

This study aims to investigate the prevalence of intestinal pathogenic Escherichia coli (InPEC) in healthy pig-related samples and evaluate the potential virulence of the InPEC strains.

METHODS AND RESULTS

A multiplex PCR method was established to identify different pathotypes of InPEC. A total of 800 rectal swab samples and 296 pork samples were collected from pig farms and slaughterhouses in Hubei province, China. From these samples, a total of 21 InPEC strains were isolated, including 19 enteropathogenic E. coli (EPEC) and 2 shiga toxin-producing E. coli (STEC) strains. By whole-genome sequencing and in silico typing, it was shown that the sequence types and serotypes were diverse among the strains. Antimicrobial susceptibility assays showed that 90.48% of the strains were multi-drug resistant. The virulence of the strains was first evaluated using the Galleria mellonella larvae model, which showed that most of the strains possessed medium to high pathogenicity. A moderately virulent EPEC isolate was further selected to characterize its pathogenicity using a mouse model, which suggested that it could cause significant diarrhea. Bioluminescence imaging (BLI) was then used to investigate the colonization dynamics of this EPEC isolate, which showed that the EPEC strain could colonize the mouse cecum for up to 5 days.

Differences in the Shiga Toxin (Stx) 2a Phage Regulatory Switch Region Influence Stx2 Localization and Virulence of Stx-Producing Escherichia coli in Mice

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne illness globally, and infection with serotype O157:H7 is associated with increased risk of hospitalization and death in the U.S. The Stxs are encoded on a temperate bacteriophage (stx-phage), and phage induction leads to Stx expression; subtype Stx2a in particular is associated with more severe disease. Our earlier studies showed significant levels of RecA-independent Stx2 production by STEC O157:H7 strain JH2010 (stx2astx2c), even though activated RecA is the canonical trigger for stx-phage induction. This study aimed to further compare and contrast RecA-independent toxin production in Stx2-producing clinical isolates. Deletion of recA in JH2010 resulted in higher in vitro supernatant cytotoxicity compared to that from JH2016ΔrecA, and the addition of the chelator ethylenediaminetetraacetic acid (EDTA) and various metal cations to the growth medium exacerbated the difference in cytotoxicity exhibited by the two deletion strains. Both the wild-type and ΔrecA deletion strains exhibited differential cytotoxicity in the feces of infected, streptomycin (Str)-treated mice. Comparison of the stx2a-phage predicted protein sequences from JH2010 and JH2016 revealed low amino acid identity of key phage regulatory proteins that are involved in RecA-mediated stx-phage induction. Additionally, other STEC isolates containing JH2010-like and JH2016-like stx2a-phage sequences led to similar Stx2 localization, as demonstrated by JH2010ΔrecA and JH2016ΔrecA, respectively. Deletion of the stx2a-phage regulatory region in the wild-type strains prevented the differential localization of Stx2 into the culture supernatant, a finding that suggests that the stx2a-phage regulatory region is involved in the differential ΔrecA phenotypes exhibited by the two strains. We hypothesize that the amino acid differences between the JH2010 and JH2016 phage repressor proteins (CIs) lead to structural differences that are responsible for differential interaction with RecA. Overall, we discovered that non-homologous stx2a-phage regulatory proteins differentially influence RecA-independent, and possibly RecA-dependent, Stx2 production. These findings emphasize the importance of studying non-homologous regulatory elements among stx2-phages and their influence on Stx2 production and virulence of STEC isolates.

Epidemiological Characterization of Isolates of Salmonella enterica and Shiga Toxin-Producing Escherichia coli from Backyard Production System Animals in the Valparaíso and Metropolitana Regions

Backyard production systems (BPS) are distributed worldwide, rearing animals recognized as reservoirs of Salmonella enterica and Shiga toxin-producing Escherichia coli (STEC), both zoonotic pathogens. The aim of this study was to characterize isolates of both pathogens obtained from animals raised in BPS from two central Chile regions. The presence of pathogens was determined by bacterial culture and confirmatory PCR for each sampled BPS, calculating positivity rates. Multivariate logistic regression was used to determine risk factors. Additionally, phenotypic antimicrobial resistance was determined. A positivity rate of 2.88% for S. enterica and 14.39% for STEC was determined for the complete study region (Valparaíso and Metropolitana regions). Risk factor analysis suggests that the presence of ruminants (OR = 1.03; 95% CI = 1.002-1.075) increases the risk of STEC-positive BPS, and the presence of ruminants (OR = 1.05; 95% CI = 1.002-1.075) and the animal handlers being exclusively women (OR = 3.54; 95% CI = 1.029-12.193) increase the risk for S. enterica/STEC positivity. Eighty percent of S. enterica isolates were multidrug resistant, and all STEC were resistant to Cephalexin. This study evidences the circulation of multidrug-resistant zoonotic bacterial strains in animals kept in BPS and the presence of factors that modify the risk of BPS positivity for both pathogens.

Study of Zoonotic Pathogens in Alien Population of Veiled Chameleons (Chamaeleo calyptratus) in the Canary Islands (Spain)

Veiled chameleons (Chamaeleo calyptratus) are native to the Arabian Peninsula that have been introduced as pets in many regions around the world, such as the Canary Islands (Spain). In this work, the gastrointestinal content from veiled chameleons of Gran Canaria island (Canary Islands) has been analyzed to determine the presence of zoonotic bacteria. Forty animals were analyzed using different selective culture media and PCR. The most isolated bacteria were Yersinia enterocolitica (52.4%), followed by Salmonella spp. (40.0%), with positive isolates for Salmonella Tyhpi and Salmonella Typhimurium. Pseudomonas spp. was found in 32.5% of the chameleons. More than half were positive for Pseudomonas aeruginosa. Antibiotic-resistant Staphylococcus spp. was detected in six animals plus one isolate of non-resistant Staphylococcus hominis. Multiple mycobacteria species belonging to both tuberculous and non-tuberculous complexes were identified as well as Escherichia coli carrying the stx₁ and eae virulence genes with 12.5% and 7.5% prevalence, respectively. Listeria monocytogenes, Campylobacter spp., and Vibrio spp. were found in lower proportion (<5%). The results obtained indicate that veiled chameleons in Gran Canaria could be playing a role in the maintenance and dissemination of the pathogens detected, harming public health and biodiversity.

Shiga Toxin (Stx) Phage-Encoded Lytic Genes Are Not Required for the Mouse Virulence of O157:H7 Escherichia coli Stx2-Producing Clinical Isolates

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne diarrheal illness in the United States and globally, and serotype O157:H7 is frequently associated with STEC outbreaks and sporadic cases in the United States. Severe systemic diseases associated with STEC are mediated by Stx types, particularly subtype Stx2a, encoded on inducible bacteriophages. We previously identified two STEC O157:H7 clinical isolates, JH2010 and JH2012, that exhibit a large difference in virulence in a streptomycin (Str)-treated mouse model. In this study, we aimed to identify a genetic basis for the difference in virulence between those strains. Comparison of the stx2a phage sequences showed that JH2012 lacks the lytic genes S and R on the phage genome. We also demonstrated that compared to JH2012 cultures, cultures of JH2010 released more Stx2 into the supernatant and were more sensitive to bacterial lysis during growth with ciprofloxacin (Cip), an inducer of stx phages. We therefore generated an stx2a phage SR deletion mutant strain of JH2010 to determine if those genes were responsible for the high virulence of that strain. We found that deletion of the SR genes from the stx2a phage in JH2010, and another O157:H7 strain, JH2016, resulted in increased cellular retention of Stx2, but there was no difference in virulence compared to the wild-type strains. Our results indicate that the stx2a phage SR genes are involved in Stx2 localization and phage-mediated cell lysis in vitro but that they are not required in wild-type STEC strains for virulence in a mouse model. IMPORTANCE The release of Stx from STEC has been thought to be tied to phage-mediated lysis of the host bacterial cell. In this study, we found that the stx2a phage lytic genes are not required for the virulence of pathogenic O157:H7 clinical isolates in a murine model of STEC infection or for release of Stx2a into the supernatant of bacterial cultures. These results point to an alternate mechanism for Stx2a release from STEC strains.

In Vitro Effect of the Cell-Free Supernatant of the Lactobacillus casei Strain IMAU60214 against the Different Pathogenic Properties of Diarrheagenic Escherichia coli

Enteroaggregative Escherichia coli (EAEC) and enterohemorrhagic E. coli (EHEC) are E. coli pathotypes associated with unmanageable diarrhea in children and adults. An alternative to the treatment of infections caused by these microorganisms is the use of the bacteria of the Lactobacillus genus; however, the beneficial effects on the intestinal mucosa are specific to the strain and species. The interest of this study consisted of analyzing the coaggregation properties of Lactobacillus casei IMAU60214, as well as the effect of cell-free supernatant (CSF) on growth and anti-cytotoxic activity in a cell model of the human intestinal epithelium for an agar diffusion assay (HT-29) and the inhibition of biofilm formation on plates of DEC strains of the EAEC and EHEC pathotypes. The results showed that L. casei IMAU60214 exhibits time-dependent coaggregation (35-40%) against EAEC and EHEC that is similar to the control E. coli ATCC 25922. The CSF showed antimicrobial activity (20-80%) against EAEC and EHEC depending on the concentration. In addition, the formation and dispersion of biofilms of the same strains decrease, and the proteolytic pre-treatment with catalase and/or proteinase K (1 mg/mL) of CSF reduces the antimicrobial effect. When evaluating the effect in HT-29 cells pre-treated with CFS on the toxic activity induced by the EAEC and EHEC strains, a reduction of between 30 and 40% was observed. The results show that L. casei IMAU60214 and its CSF have properties that interfere with some properties associated with the virulence of the EAEC and EHEC strains that cause intestinal infection, which supports their use for the control and prevention of infections caused by these bacteria.

Genome-wide association study of hemolytic uremic syndrome causing Shiga toxin-producing Escherichia coli from Sweden, 1994-2018

Shiga toxin-producing Escherichia coli (STEC) infection can cause clinical manifestations ranging from diarrhea to potentially fatal hemolytic uremic syndrome (HUS). This study is aimed at identifying STEC genetic factors associated with the development of HUS in Sweden. A total of 238 STEC genomes from STEC-infected patients with and without HUS between 1994 and 2018 in Sweden were included in this study. Serotypes, Shiga toxin gene (stx) subtypes, and virulence genes were characterized in correlation to clinical symptoms (HUS and non-HUS), and pan-genome wide association study was performed. Sixty-five strains belonged to O157:H7, and 173 belonged to non-O157 serotypes. Our study revealed that strains of O157:H7 serotype especially clade 8 were most commonly found in patients with HUS in Sweden. stx2a and stx2a + stx2c subtypes were significantly associated with HUS. Other virulence factors associated with HUS mainly included intimin (eae) and its receptor (tir), adhesion factors, toxins, and secretion system proteins. Pangenome wide-association study identified numbers of accessory genes significantly overrepresented in HUS-STEC strains, including genes encoding outer membrane proteins, transcriptional regulators, phage-related proteins, and numerous genes related to hypothetical proteins. Whole-genome phylogeny and multiple correspondence analysis of pangenomes could not differentiate HUS-STEC from non-HUS-STEC strains. In O157:H7 cluster, strains from HUS patients clustered closely; however, no significant difference in virulence genes was found in O157 strains from patients with and without HUS. These results suggest that STEC strains from different phylogenetic backgrounds may independently acquire genes determining their pathogenicity and confirm that other non-bacterial factors and/or bacteria-host interaction may affect STEC pathogenesis.

Pathophysiology of Enteropathogenic Escherichia coli-induced Diarrhea

Enteropathogenic Escherichia coli (EPEC) are important diarrheal pathogens of infants and young children. Since the availability of molecular diagnosis methods, we now have new insights into the incidence and prevalence of these infections. Recent epidemiological studies indicate that atypical EPEC (aEPEC) are seen more frequently than typical EPEC (tEPEC) worldwide, including in both endemic diarrhea and diarrhea outbreaks. Therefore, it is important to further characterize the pathogenicity of these emerging strains. The virulence mechanisms and pathophysiology of the attaching and effacing lesion (A/E) and the type-three-secretion-system (T3SS) are complex but well-studied. A/E strains use their pool of locus of enterocyte effacement (LEE)-encoded and non-LEE-encoded effector proteins to subvert and modulate cellular and barrier properties of the host. However, the exact mechanisms of diarrhea in EPEC infection are not completely understood. From the clinical perspective, there is a need for fast, easy, and inexpensive diagnostic methods to define optimal treatment and prevention for children in endemic areas. In this article, we present a review of the classification of EPEC, epidemiology, pathogenesis of the disease caused by these bacteria, determinants of virulence, alterations in signaling, determinants of colonization vs. those of disease, and the limited information we have on the pathophysiology of EPEC-induced diarrhea. This article combines peer-reviewed evidence from our own studies and the results of an extensive literature search in the databases PubMed, EMBASE, and Scopus.

Regulation of flagellar motility and biosynthesis in enterohemorrhagic Escherichia coli O157:H7

ABSTARCTEnterohemorrhagic Escherichia coli (EHEC) O157:H7 is a human pathogen that causes a variety of diseases, such as hemorrhagic colitis and lethal hemolytic uremic syndrome. Flagellum-dependent motility plays diverse roles in the pathogenesis of EHEC O157:H7, including its migration to an optimal host site, adherence and colonization, survival at the infection site, and post-infection dispersal. However, it is very expensive for cellular economy in terms of the number of genes and the energy required for flagellar biosynthesis and functioning. Furthermore, the flagellar filament bears strong antigenic properties that induce a strong host immune response. Consequently, the flagellar gene expression and biosynthesis are highly regulated to occur at the appropriate time and place by different regulatory influences. The present review focuses on the regulatory mechanisms of EHEC O157:H7 motility and flagellar biosynthesis, especially in terms of flagellar gene regulation by environmental factors, regulatory proteins, and small regulatory RNAs.

Comparative Genomics of Shiga Toxin-Producing Escherichia coli Strains Isolated from Pediatric Patients with and without Hemolytic Uremic Syndrome from 2000 to 2016 in Finland

Shiga toxin-producing Escherichia coli (STEC) infection can cause mild to severe illness, such as nonbloody or bloody diarrhea, and the fatal hemolytic uremic syndrome (HUS). The molecular mechanism underlying the variable pathogenicity of STEC infection is not fully defined so far. Here, we performed a comparative genomics study on a large collection of clinical STEC strains collected from STEC-infected pediatric patients with and without HUS in Finland over a 16-year period, aiming to identify the bacterial genetic factors that can predict the risk to cause HUS and poor renal outcome. Of 240 STEC strains included in this study, 52 (21.7%) were from pediatric patients with HUS. Serotype O157:H7 was the main cause of HUS, and Shiga toxin gene subtype stx2a was significantly associated with HUS. Comparative genomics and pangenome-wide association studies identified a number of virulence and accessory genes overrepresented in HUS-associated STEC compared to non-HUS STEC strains, including genes encoding cytolethal distending toxins, type III secretion system effectors, adherence factors, etc. No virulence or accessory gene was significantly associated with risk factors for poor renal outcome among HUS patients assessed in this study, including need for and duration of dialysis, presence and duration of anuria, and leukocyte counts. Whole-genome phylogeny and multiple-correspondence analysis of pangenomes could not separate HUS STEC from non-HUS STEC strains, suggesting that STEC strains with diverse genetic backgrounds may independently acquire genetic elements that determine their varied pathogenicity. Our findings indicate that nonbacterial factors, i.e., characteristics of the host immunity, might affect STEC virulence and clinical outcomes.

IMPORTANCE Shiga toxin-producing Escherichia coli (STEC) is a serious public health burden worldwide which causes outbreaks of gastrointestinal diseases and the fatal hemolytic uremic syndrome (HUS) characterized by the triad of mechanical hemolytic anemia, thrombocytopenia, and acute renal failure. Understanding the mechanism underlying the disease severity and patient outcome is of high importance. Using comparative genomics on a large collection of clinical STEC strains from STEC-infected patients with and without HUS, our study provides a reference of STEC genetic factors/variants that can be used as predictors of the development of HUS, which will aid risk assessment at the early stage of STEC infection. Additionally, our findings suggest that nonbacterial factors may play a primary role in the renal outcome in STEC-infected patients with HUS; further studies are needed to validate this.

Formation and Transfer of Multi-Species Biofilms Containing E. coli O103:H2 on Food Contact Surfaces to Beef

Interactions of Shiga toxin–producing E. coli (STEC; O103:H2) with lactic acid bacteria (LAB) or spoilage bacteria (SP) multispecies biofilms on polyurethane (TPU) and stainless-steel (SS) were assessed at 10 and 25°C under wet and dry conditions after 6, 30, and 60 days of storage. One LAB T1: Carnobacterium piscicola + Lactobacillus bulgaricus, and two SP T2: Comamonas koreensis + Raoultella terrigena; T3: Pseudomonas aeruginosa + C. koreensis were assessed for their ability to form multispecies biofilms with O103:H2. O103:H2 single-species biofilms served as a control positive (T4). Coupons were stored dry (20–50% relative humidity; RH) or moist (60–90% RH) for up to 60 days, at which point O103:H2 transfer to beef and survival was evaluated. At 25°C, T3 decreased beef contamination with O103:H2 by 2.54 log₁₀ CFU/g (P < 0.001). Overall, at 25°C contamination of beef with O103:H2 decreased (P < 0.001) from 3.17 log₁₀ CFU/g on Day 6 to 0.62 log₁₀ CFU/g on Day 60. With 60 days dry biofilms on TPU, an antagonistic interaction was observed among O103:H2 and multispecies biofilm T1 and T3. E. coli O103:H2 was not recovered from T1 and T3 after 60 days but it was recovered (33%) from T2 and T4 dry biofilms. At 10°C, contamination of beef with O103:H2 decreased (P < 0.001) from 1.38 log₁₀ CFU/g after 6 days to 0.47 log₁₀ CFU/g after 60 days. At 10°C, recovery of O103:H2 from 60 days dry biofilms could only be detected after enrichment and was always higher for T2 than T4 biofilms. Regardless of temperature, the transfer of O103:H2 to beef from the biofilm on TPU was greater (P < 0.001) than SS. Moist biofilms also resulted in greater (P < 0.001) cell transfer to beef than dry biofilms at 10 and 25°C. Development of SP or LAB multispecies biofilms with O103:H2 can either increase or diminish the likelihood of beef contamination. Environmental conditions such as humidity, contact surface type, as well as biofilm aging all can influence the risk of beef being contaminated by STEC within multi-species biofilms attached to food contact surfaces.

Genomic Characterization of Escherichia coli O8 Strains Producing Shiga Toxin 2l Subtype

Shiga toxin-producing Escherichia coli (STEC) can cause diseases ranging from mild diarrhea to fatal extra-intestinal hemolytic uremic syndrome (HUS). Shiga toxin (Stx) is the key virulence factor in STEC, two Stx types (Stx1 and Stx2) and several subtypes varying in sequences, toxicity, and host specificity have been identified. Stx2l is a newly-designated subtype related to human disease but lacks thorough characterization. Here, we identified Stx2l from five STEC strains (Stx2l-STECs) recovered from raw mutton and beef in China. Whole-genome sequencing (WGS) was used to characterize the Stx2l-STECs in this study together with Stx2l-STECs retrieved from public databases. Our study revealed that all the analyzed Stx2l-STEC strains belonged to the same serogroup O8. Multilocus sequencing typing (MLST) showed two sequence types (ST88 and ST23) among these strains. Stx2l-converting prophages from different sources shared a highly similar structure and sequence. Single-nucleotide polymorphism (SNP)-based analysis revealed genetic relatedness between the human-derived and food-derived strains belonging to ST23. To conclude, our study supported the designation of Stx2l and demonstrated diverse host range and geographical distribution of Stx2l-STECs.Stx2l-STEC strains from different sources showed a high genetic similarity with an identical O8 serogroup. Further studies are needed to investigate the epidemiological trait and pathogenic potential of Stx2l-STEC strains.

Examining the role of person-to-person transmission during a verocytotoxigenic Escherichia coli outbreak in Ontario, Canada

OBJECTIVE

Person-to-person transmission can occur during outbreaks of verotoxigenic Escherichia coli (VTEC), however the impact of this transmission route is not well understood. This study aimed to examine the role of person-to-person transmission during a VTEC outbreak, and how targeting this route may reduce outbreak size. A deterministic compartmental model describing a VTEC outbreak was constructed and fit to data from a 2008 outbreak in Ontario, Canada. Using the best-fit model, simulations were run to calculate the: reduction in transmission rate after implementing interventions, proportion of cases infected through both transmission routes, and number of cases prevented by interventions. Latin hypercube sensitivity analysis was conducted to examine the sensitivity of the outbreak size to the model parameters.

RESULTS

Based on the best-fit model, ~ 14.25% of the cases likely arose due to person-to-person transmission. Interventions reduced this transmission rate by ~ 73%, causing a reduction in outbreak size of ~ 17% (47 cases). Sensitivity analysis showed that the model was highly sensitive to changes in all parameters of the model. The model demonstrates that person-to-person could be an important transmission route during VTEC outbreaks. Targeting this route of transmission through hand hygiene and work exclusions could reduce the final outbreak size.

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.

A trait-based framework for predicting foodborne pathogen risk from wild birds

Recent foodborne illness outbreaks have heightened pressures on growers to deter wildlife from farms, jeopardizing conservation efforts. However, it remains unclear which species, particularly birds, pose the greatest risk to food safety. Using >11,000 pathogen tests and 1565 bird surveys covering 139 bird species from across the western United States, we examined the importance of 11 traits in mediating wild bird risk to food safety. We tested whether traits associated with pathogen exposure (e.g., habitat associations, movement, and foraging strategy) and pace-of-life (clutch size and generation length) mediated foodborne pathogen prevalence and proclivities to enter farm fields and defecate on crops. Campylobacter spp. were the most prevalent enteric pathogen (8.0%), while Salmonella and Shiga-toxin producing Escherichia coli (STEC) were rare (0.46% and 0.22% prevalence, respectively). We found that several traits related to pathogen exposure predicted pathogen prevalence. Specifically, Campylobacter and STEC-associated virulence genes were more often detected in species associated with cattle feedlots and bird feeders, respectively. Campylobacter was also more prevalent in species that consumed plants and had longer generation lengths. We found that species associated with feedlots were more likely to enter fields and defecate on crops. Our results indicated that canopy-foraging insectivores were less likely to deposit foodborne pathogens on crops, suggesting growers may be able to promote pest-eating birds and birds of conservation concern (e.g., via nest boxes) without necessarily compromising food safety. As such, promoting insectivorous birds may represent a win-win-win for bird conservation, crop production, and food safety. Collectively, our results suggest that separating crop production from livestock farming may be the best way to lower food safety risks from birds. More broadly, our trait-based framework suggests a path forward for co-managing wildlife conservation and food safety risks in farmlands by providing a strategy for holistically evaluating the food safety risks of wild animals, including under-studied species.

Nanobody-Based Bispecific Neutralizer for Shiga Toxin-Producing E. coli

Currently, no specific therapeutics are available for foodborne Shiga toxin-producing Escherichia coli (STEC) infections that cause severe gastroenteritis and life-threatening complications of hemolytic uremic syndrome (HUS). As STEC attachment to intestinal epithelium might increase the host absorption of Shiga toxins and severity of the disease, we were inspired to develop a bispecific neutralizer capable of blocking its Shiga toxin and adhesin intimin simultaneously. Two nanobodies against the B subunit of Shiga toxin 2 (Stx2B) and the C terminus of Intimin (IntC280) were genetically fused together as the bispecific neutralizer, and it can be efficiently produced in a conventional E. coli expression system. We demonstrated that each of the nanobody modules in the bispecific format showed increased antigen binding capability and was able to functionally neutralize the binding of Stx2B or IntC280 to the respective host receptors even in the presence of the two virulence factors together. Moreover, the bispecific neutralizer was relatively stable to harsh storage conditions and gastrointestinal pH extremes. Taking into account its easy and economical production and superior pharmaceutical properties, we believe that a nanobody-based bispecific neutralizer would be more favorable and practical to be developed as a therapeutic to fight STEC in the developing world.

Molecular Detection of Non-O157 Shiga Toxin-Producing Escherichia coli (STEC) Directly from Stool Using Multiplex qPCR Assays

Non-O157 Shiga toxin-producing E. coli (STEC) can cause outbreaks that have great economic and health impact. Since the implementation of STEC screening in Alberta in 2018, it is also essential to have a molecular serotyping method with faster turnaround time for cluster identification and surveillance purposes. This study sought to perform molecular serotyping of the top six non-O157 (O26, O45, O103, O111, O121 and O145) STEC serotypes directly from stools and enrichment broths compared to conventional methods on isolates. Multiplex, serotyping qPCR assays were used to determine sensitivity and specificity of the top six non-O157 STEC serotypes. Sensitivity and specificity were assessed for both singleplex and multiplex qPCR assays for comparison of the top six serotypes. Blinded stool specimens (n = 116) or broth samples (n = 482) submitted from frontline microbiology laboratories for STEC investigation were analyzed by qPCR. Both singleplex and multiplex assays were comparable, and we observed 100% specificity with a limit of detection of 100 colony-forming units per mL. Direct molecular serotyping from stool specimens mostly correlated (88%) with conventional serotyping of the cultured isolate. In cases of discordant serotypes, the top six non-O157 STEC mixed infections were identified and confirmed by culture and conventional serotyping. Detection of non-O157 STEC can be done directly from stool specimens using multiplex PCR assays with the ability to identify mixed infections, which would otherwise remain undetected by conventional serotyping of a single colony. This method can be easily implemented into a frontline diagnostic laboratory to enhance surveillance of non-O157 STEC, as more frontline microbiology laboratories move to culture independent assays.

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

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

High prevalence and pathogenic potential of Shiga toxin-producing Escherichia coli strains in raw mutton and beef in Shandong, China

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen that can cause severe human diseases such as hemolytic uremic syndrome (HUS). Human STEC infections are frequently caused through consumption of contaminated foods, especially raw meats. This study aimed to investigate the prevalence of STEC in raw meats and to characterize the meat-derived STEC strains using whole genome sequencing. Our study showed that 26.6% of raw mutton, and 7.5% of raw beef samples were culture-positive for STEC. Thirteen serotypes were identified in 22 meat-derived isolates in this study, including the virulent serotypes O157:H7 and O26:H11. Seven Shiga toxin (Stx) subtypes were found in 22 isolates, of these, stx1c and stx1c + stx2b were predominant. The recently-reported stx2k subtype was found in three mutton-sourced isolates. A number of other virulence genes such as genes encoding intimin (eae), enterohemorrhagic E. coli (EHEC) hemolysin (ehxA), EHEC factor for adherence (efa1), heat-stable enterotoxin 1 (astA), type III secretion system effectors, were detected in meat-derived STEC strains. One mutton-sourced isolate was resistant to three antibiotics, i.e., tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole. Whole-genome phylogeny indicated the genomic diversity of meat-derived strains in this study. O157:H7 and O26:H11 isolates in this study were phylogenetically grouped together with strains from HUS patients, suggesting their pathogenic potential. To conclude, our study reported high STEC contaminations in retail raw meats, particularly raw mutton, genomic characterization indicated pathogenic potential of meat-derived STEC strains. These findings highlight the critical need for increased monitoring of STEC in retail raw meats in China.

•

High prevalence of Shiga toxin-producing E. coli (STEC) was detected in raw mutton, compared to beef.

•

Virulent serotypes O157:H7 and O26:H11 were found in meat-sourced STEC isolates.

•

Meat-sourced STEC isolates in the same region exhibited genetic diversity.

Genomic Characteristics of Stx2e-Producing Escherichia coli Strains Derived from Humans, Animals, and Meats

Shiga toxin (Stx) can be classified into two types, Stx1 and Stx2, and different subtypes. Stx2e is a subtype commonly causing porcine edema disease and rarely reported in humans. The purpose of this study was to analyze the prevalence and genetic characteristics of Stx2e-producing Escherichia coli (Stx2e-STEC) strains from humans compared to strains from animals and meats in China. Stx2e-STEC strains were screened from our STEC collection, and whole-genome sequencing was performed to characterize their genetic features. Our study showed a wide distribution of Stx2e-STEC among diverse hosts and a higher proportion of Stx2e-STEC among human STEC strains in China. Three human Stx2e-STEC isolates belonged to O100:H30, Onovel26:H30, and O8:H9 serotypes and varied in genetic features. Human Stx2e-STECs phylogenetically clustered with animal- and food-derived strains. Stx2e-STEC strains from animals and meat showed multidrug resistance, while human strains were only resistant to azithromycin and tetracycline. Of note, a high proportion (55.9%) of Stx2e-STEC strains, including one human strain, carried the heat-stable and heat-labile enterotoxin-encoding genes st and lt, exhibiting a STEC/enterotoxigenic E. coli (ETEC) hybrid pathotype. Given that no distinct genetic feature was found in Stx2e-STEC strains from different sources, animal- and food-derived strains may pose the risk of causing human disease.

Identification of Shiga-Toxin-Producing Shigella Infections in Travel and Non-Travel Related Cases in Alberta, Canada

It has long been accepted that Shiga toxin (Stx) only exists in Shigella dysenteriae serotype 1. However, in recent decades, the presence of Shiga toxin genes (stx) in other Shigella spp. have been reported. We screened 366 Shigella flexneri strains from Alberta, Canada (2003 to 2016) for stx and 26 positive strains were identified. These isolates are highly related with the majority originating from the Dominican Republic and three isolates with Haiti origin. Both phylogenetic and spanning tree analysis of the 26 Alberta and 29 stx positive S. flexneri originating from the U.S., France, Canada (Quebec) and Haiti suggests that there are geographic specific distribution patterns (Haiti and Dominican Republic clades). This study provides the first comprehensive whole genome based phylogenetic analysis of stx positive S. flexneri strains as well as their global transmission, which signify the public health risks of global spreading of these strains.

Risk Factors for Positivity to Shiga Toxin-Producing Escherichia coli and Salmonella enterica in Backyard Production Systems Animals from Metropolitana Region, Chile: A Threat to Public Health?

In the Metropolitana region of Chile there are 3836 backyard production systems (BPS), characterized as small-scale systems. They act as a source of zoonotic pathogens, such as Salmonella enterica and Shiga toxin-producing Escherichia coli (STEC), whose prevalence in BPS has not been fully described. The objective of this study was to determine the positivity for both agents in BPS and to establish the risk factors related to their presence. In each BPS, an epidemiological survey was undertaken, and stool samples were collected to detect these pathogens via bacteriological culture and conventional PCR techniques. Subsequently, multivariable logistic regression models were applied to establish the risk factors associated with their presence. BPS positivity rates of 11.76% for STEC and 4.7% for S. enterica were observed. The systems showed poor welfare standards and a lack of biosecurity measures. The risk factor analysis concluded that the Gini–Simpson index (p = 0.030; OR = 1.717) and the presence of neighboring intensive poultry or swine production systems (p = 0.019; OR = 20.645) act as factors that increased the risk of positivity with respect to STEC. In the case of S. enterica, exchanging embryonated eggs (p = 0.021; OR = 39) and the presence of debeaked chickens (p = 0.001; OR = 156) were determined as factors that increased the risk of positivity for this agent. For positivity with respect to both pathogens, the Gini–Simpson index (p = 0.030; OR = 1.544) and being INDAP/PRODESAL users (p = 0.023; OR = 15.026) were determined as factors that increased the risk, whereas the type of confinement (p = 0.002; OR = 0.019) decreased it. Epidemiological surveillance of these neglected populations is lacking, highlighting the fact that STEC and S. enterica maintenance on BPS represents a potential threat to public health.

Adult Shigatoxin-mediated hemolytic uremic syndrome masked by alcohol use and inflammatory bowel disease

Diagnosing uncommon diseases in individuals with underlying medical conditions can be challenging. Cognitive bias can lead to delayed or missed disease management. We present a case of Shiga-toxin mediated hemolytic uremic syndrome (ST-HUS) in a 46-year-old man with ulcerative colitis and alcohol use disorder who presented with acute alcohol intoxication, non-bloody diarrhoea and coffee ground emesis. He was admitted to the hospital for alcoholic ketoacidosis, alcohol withdrawal and possible upper gastrointestinal bleed, but ultimately, he developed severe thrombocytopaenia, hemolytic anaemia, acute renal failure and prolonged altered mentation. Given that ST-HUS is uncommon in adults, his initial report of diarrhoea was attributed to alcohol use or underlying active ulcerative colitis and not connected to his haematologic abnormalities. He was initially started on plasmapheresis; however, thrombotic microangiopathy work up revealed Shiga-toxin in his stool and ADAMST13 levels within normal limits. Subsequently, he was transitioned to supportive care for management of ST-HUS.

Evaluation of the eazyplex® EHEC complete (Amplex) assay for the differentiation of stx1 and stx2 positivity in stool samples

The performance of the eazyplex® EHEC complete (Amplex) for the detection of Shiga toxin genes in stool samples was evaluated. The assay performed well in distinguishing between stx1 and stx2 but suboptimal sensitivity may limit its use to complementary testing rather than primary diagnosis of Shiga toxin-producing Escherichia coli infections.

Whole-genome characterization of hemolytic uremic syndrome-causing Shiga toxin-producing Escherichia coli in Sweden

Shiga toxin-producing Escherichia coli, a foodborne bacterial pathogen, has been linked to a broad spectrum of clinical outcomes ranging from asymptomatic carriage to fatal hemolytic uremic syndrome (HUS). Here, we collected clinical data and STEC strains from HUS patients from 1994 through 2018, whole-genome sequencing was performed to molecularly characterize HUS-associated STEC strains, statistical analysis was conducted to identify bacterial genetic factors associated with severe outcomes in HUS patients. O157:H7 was the most predominant serotype (57%) among 54 HUS-associated STEC strains, followed by O121:H19 (19%) and O26:H11 (7%). Notably, some non-predominant serotypes such as O59:H17 (2%) and O109:H21 (2%) also caused HUS. All O157:H7 strains with one exception belonged to clade 8. During follow-up at a median of 4 years, 41% of the patients had renal sequelae. Fifty-nine virulence genes were found to be statistically associated with severe renal sequelae, these genes encoded type II and type III secretion system effectors, chaperones, and other factors. Notably, virulence genes associated with severe clinical outcomes were significantly more prevalent in O157:H7 strains. In contrast, genes related to mild symptoms were evenly distributed across all serotypes. The whole-genome phylogeny indicated high genomic diversity among HUS-STEC strains. No distinct cluster was found between HUS and non-HUS STEC strains. The current study showed that O157:H7 remains the main cause of STEC-associated HUS, despite the rising importance of other non-O157 serotypes. Besides, O157:H7 is associated with severe renal sequelae in the follow-up, which could be a risk factor for long-term prognosis in HUS patients.

Non-Digestible Oligosaccharides and Short Chain Fatty Acids as Therapeutic Targets against Enterotoxin-Producing Bacteria and Their Toxins

Enterotoxin-producing bacteria (EPB) have developed multiple mechanisms to disrupt gut homeostasis, and provoke various pathologies. A major part of bacterial cytotoxicity is attributed to the secretion of virulence factors, including enterotoxins. Depending on their structure and mode of action, enterotoxins intrude the intestinal epithelium causing long-term consequences such as hemorrhagic colitis. Multiple non-digestible oligosaccharides (NDOs), and short chain fatty acids (SCFA), as their metabolites produced by the gut microbiota, interact with enteropathogens and their toxins, which may result in the inhibition of the bacterial pathogenicity. NDOs characterized by diverse structural characteristics, block the pathogenicity of EPB either directly, by inhibiting bacterial adherence and growth, or biofilm formation or indirectly, by promoting gut microbiota. Apart from these abilities, NDOs and SCFA can interact with enterotoxins and reduce their cytotoxicity. These anti-virulent effects mostly rely on their ability to mimic the structure of toxin receptors and thus inhibiting toxin adherence to host cells. This review focuses on the strategies of EPB and related enterotoxins to impair host cell immunity, discusses the anti-pathogenic properties of NDOs and SCFA on EPB functions and provides insight into the potential use of NDOs and SCFA as effective agents to fight against enterotoxins.

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.

Thin-Layer Chromatography in Structure and Recognition Studies of Shiga Toxin Glycosphingolipid Receptors

Glycosphingolipids (GSLs) consist of a ceramide (Cer) lipid anchor, which is typically composed of the long-chain aminoalcohol sphingosine (d18:1) and a fatty acid (mostly C16-C24) and a sugar moiety harboring to a great extent one to five monosaccharides. GSLs of the globo-series are well-recognized receptors of Shiga toxins (Stxs) released by Stx-producing Escherichia coli (STEC). Receptors for the Stx subtypes Stx1a and Stx2a are globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer), whereby Gb3Cer represents their high-affinity and Gb4Cer their low-affinity receptor. In addition to Gb3Cer and Gb4Cer, Gb5Cer and Forssman GSL are further receptors of the Stx2e subtype rendering Stx2e unique among the various Stx subtypes. Thin-layer chromatography (TLC) is a convenient and ubiquitously employed method for analyzing GSL mixtures of unknown composition. In particular, TLC immunochemical overlay detection allows for sensitive identification of Stx-binding GSLs in complex mixtures directly on the TLC plate. For this purpose, specific anti-GSL antibodies or Stxs themselves in conjunction with anti-Stx antibodies can be used. The described protocols of antibody-mediated detection of TLC-separated globo-series GSLs and corresponding identification of Stx-binding globo-series GSLs will provide detailed advice for successful GSL analysis and particularly highlight the power of the TLC overlay technique.

Association of Ct Values from Real-Time PCR with Culture in Microbiological Clearance Samples for Shiga Toxin-Producing Escherichia coli (STEC)

Shiga toxin-producing Escherichia coli (STEC) are associated with acute gastroenteritis worldwide, which induces a high economic burden on both healthcare and individuals. Culture-independent diagnostic tests (CIDT) in frontline microbiology laboratories have been implemented in Alberta since 2019. The objectives of this study were to determine the association between gene detection and culture positivity over time using STEC microbiological clearance samples and also to establish the frequency of specimen submission. Both stx genes’ amplification by real-time PCR was performed with DNA extracted from stool samples using the easyMAG system. Stools were inoculated onto chromogenic agar for culture. An association between gene detection and culture positivity was found to be independent of which stx gene was present. CIDT can provide rapid reporting with less hands-on time and technical expertise. However, culture is still important for surveillance and early cluster detection. In addition, stool submissions could be reduced from daily to every 3–5 days until a sample is negative by culture.

Diversity in E. coli (p)ppGpp Levels and Its Consequences

(p)ppGpp is at the core of global bacterial regulation as it controls growth, the most important aspect of life. It would therefore be expected that at least across a species the intrinsic (basal) levels of (p)ppGpp would be reasonably constant. On the other hand, the historical contingency driven by the selective pressures on bacterial populations vary widely resulting in broad genetic polymorphism. Given that (p)ppGpp controls the expression of many genes including those involved in the bacterial response to environmental challenges, it is not surprising that the intrinsic levels of (p)ppGpp would also vary considerably. In fact, null mutations or less severe genetic polymorphisms in genes associated with (p)ppGpp synthesis and hydrolysis are common. Such variation can be observed in laboratory strains, in natural isolates as well as in evolution experiments. High (p)ppGpp levels result in low growth rate and high tolerance to environmental stresses. Other aspects such as virulence and antimicrobial resistance are also influenced by the intrinsic levels of (p)ppGpp. A case in point is the production of Shiga toxin by certain E. coli strains which is inversely correlated to (p)ppGpp basal level. Conversely, (p)ppGpp concentration is positively correlated to increased tolerance to different antibiotics such as β-lactams, vancomycin, and others. Here we review the variations in intrinsic (p)ppGpp levels and its consequences across the E. coli species.

Primary Human Derived Blood Outgrowth Endothelial Cells: An Appropriate In Vitro Model to Study Shiga Toxin Mediated Damage of Endothelial Cells

Hemolytic uremic syndrome (HUS) is a rare disease primarily characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. Endothelial damage is the hallmark of the pathogenesis of HUS with an infection with the Shiga toxin (Stx) producing Escherichia coli (STEC-HUS) as the main underlying cause in childhood. In this study, blood outgrowth endothelial cells (BOECs) were isolated from healthy donors serving as controls and patients recovered from STEC-HUS. We hypothesized that Stx is more cytotoxic for STEC-HUS BOECs compared to healthy donor control BOECs explained via a higher amount of Stx bound to the cell surface. Binding of Shiga toxin-2a (Stx2a) was investigated and the effect on cytotoxicity, protein synthesis, wound healing, and cell proliferation was studied in static conditions. Results show that BOECs are highly susceptible for Stx2a. Stx2a is able to bind to the cell surface of BOECs with cytotoxicity in a dose-dependent manner as a result. Pre-treatment with tumor necrosis factor alpha (TNF-α) results in enhanced Stx binding with 20–30% increased lactate dehydrogenase (LDH) release. Endothelial wound healing is delayed in a Stx2a-rich environment; however, this is not caused by an effect on the proliferation rate of BOECs. No significant differences were found between control BOECs and BOECs from recovered STEC-HUS patients in terms of Stx2a binding and inhibition of protein synthesis.

Investigation on the Evolution of Shiga Toxin-Converting Phages Based on Whole Genome Sequencing

Bacteriophages are pivotal elements in the dissemination of virulence genes. The main virulence determinants of Shiga Toxin producing E. coli, Shiga Toxins (Stx), are encoded by genes localized in the genome of lambdoid bacteriophages. Stx comprise two antigenically different types, Stx1 and Stx2, further divided into subtypes. Among these, certain Stx2 subtypes appear to be more commonly occurring in the most severe forms of the STEC disease, haemorrhagic colitis and haemolytic uremic syndrome (HUS). This study aimed at obtaining insights on the evolution of Stx2 bacteriophages, due to their relevance in public health, and we report here on the analysis of the genomic structure of Stx2 converting phages in relation with the known reservoir of the E. coli strains harboring them. Stx2-converting phages conveying the genes encoding different stx2 subtypes have been isolated from STEC strains and their whole genomes have been sequenced, analyzed and compared to those of other Stx2 phages available in the public domain. The phages' regions containing the stx2 genes have been analyzed in depth allowing to make inference on the possible mechanisms of selection and maintenance of certain Stx2 phages in the reservoir. The "stx regions" of different stx2 gene subtypes grouped into three different evolutionary lines in the comparative analysis, reflecting the frequency with which these subtypes are found in different animal niches, suggesting that the colonization of specific reservoir by STEC strains could be influenced by the Stx phage that they carry. Noteworthy, we could identify the presence of nanS-p gene exclusively in the "stx regions" of the phages identified in STEC strains commonly found in cattle. As a matter of fact, this gene encodes an esterase capable of metabolizing sialic acids produced by submaxillary glands of bovines and present in great quantities in their gastrointestinal tract.

Differentiation of stx1A gene for detection of Escherichia coli serotype O157: H7 and Shigella dysenteriae type 1 in food samples using high resolution melting curve analysis

Escherichia coli serotype O157: H7 and Shigella dysenteriae type 1 as the Shiga toxin-producing bacteria cause some acute gastrointestinal and extraintestinal diseases such as hemorrhagic uremic syndrome and bloody diarrhea in human. Stx genes are the key virulence factors in these pathogens. The aim of this study was to develop HRMA assay to differentiate stx1A gene for detection of E. coli serotype O157: H7 and Sh. dysenteriae type 1 and determine the prevalence of these pathogens in food samples using this method. PCR-HRMA assay and gold standard methods have been carried out for identification of pathogens among 135 different food samples. We found HRMA method a sensitive and specific assay (100 and 100%, respectively) for differentiation of stx1A gene, consequently, detection of these pathogens in food samples. Also, the highest prevalence of E. coli serotype O157: H7 and Sh. dysenteriae type 1 harboring stx1A gene was observed in raw milk and vegetable salad samples, respectively. HRMA as a rapid, inexpensive, sensitive and specific method is suggested to be used for differentiation of stx1A gene to detect E. coli serotype O157: H7 and Sh. dysenteriae type 1 as the key pathogens for safety evaluation of food samples.

Construction of a Lectin-Glycan Interaction Network from Enterohemorrhagic Escherichia coli Strains by Multi-omics Analysis

Enterohemorrhagic Escherichia coli (EHEC) causes hemorrhagic colitis and hemolytic uremic syndrome. EHEC infection begins with bacterial adherence to the host intestine via lectin-like adhesins that bind to the intestinal wall. However, EHEC-related lectin–glycan interactions (LGIs) remain unknown. Here, we conducted a genome-wide investigation of putative adhesins to construct an LGI network. We performed microarray-based transcriptomic and proteomic analyses with E. coli EDL933. Using PSORTb-based analysis, potential outer-membrane-embedded adhesins were predicted from the annotated genes of 318 strains. Predicted proteins were classified using TMHMM v2.0, SignalP v5.0, and LipoP v1.0. Functional and protein–protein interaction analyses were performed using InterProScan and String databases, respectively. Structural information of lectin candidate proteins was predicted using Iterative Threading ASSEmbly Refinement (I-TASSER) and Spatial Epitope Prediction of Protein Antigens (SEPPA) tools based on 3D structure and B-cell epitopes. Pathway analysis returned 42,227 Gene Ontology terms; we then selected 2585 lectin candidate proteins by multi-omics analysis and performed homology modeling and B-cell epitope analysis. We predicted a total of 24,400 outer-membrane-embedded proteins from the genome of 318 strains and integrated multi-omics information into the genomic information of the proteins. Our integrated multi-omics data will provide a useful resource for the construction of LGI networks of E. coli.

Virulence and Antibiotic Resistance Patterns in E. coli, Morocco

Of 28 non-duplicate isolates of Escherichia coli recovered from yellow-legged Larus michahellis in Morocco, 92.86% were resistant to more than three antibiotics and 71.4% were multidrug resistant. Phylogenetic group A was most predominant (57.14%), followed by B1 (18%), B2 (14.28%) and F (10.71%). One isolate was resistant to ertapenem and contained the bla_OXA-48 gene. The plasmid-mediated quinolone resistance determinants were detected in nine isolates (aac(6')-Ib-cr, qnrS1, qnrB1). Thirteen isolates carried one of the Shiga toxin E. coli-associated genes: stx1 (n = 6), stx2 (n = 5) and eae (n = 2) genes. Our data support the idea that gull feces may create potential public health risk.

Genetic Susceptibility to Postdiarrheal Hemolytic-Uremic Syndrome After Shiga Toxin-Producing Escherichia coli Infection: A Centers for Disease Control and Prevention FoodNet Study

Background

Postdiarrheal hemolytic-uremic syndrome (D+HUS) following Shiga toxin-producing Escherichia coli (STEC) infection is a serious condition lacking specific treatment. Host immune dysregulation and genetic susceptibility to complement hyperactivation are implicated in non-STEC-related HUS. However, genetic susceptibility to D+HUS remains largely uncharacterized.

Methods

Patients with culture-confirmed STEC diarrhea, identified through the Centers for Disease Control and Prevention FoodNet surveillance system (2007-2012), were serotyped and classified by laboratory and/or clinical criteria as having suspected, probable, or confirmed D+HUS or as controls and underwent genotyping at 200 loci linked to nondiarrheal HUS or similar pathologies. Genetic associations with D+HUS were explored by multivariable regression, with adjustment for known risk factors.

Results

Of 641 enrollees with STEC O157:H7, 80 had suspected D+HUS (41 with probable and 32 with confirmed D+HUS). Twelve genes related to cytokine signaling, complement pathways, platelet function, pathogen recognition, iron transport, and endothelial function were associated with D+HUS in multivariable-adjusted analyses (P ≤ .05). Of 12 significant single-nucleotide polymorphisms (SNPs), 5 were associated with all levels of D+HUS (intergenic SNP rs10874639, TFRC rs3804141, EDN1 rs5370, GP1BA rs121908064, and B2M rs16966334), and 7 SNPs (6 non-complement related) were associated with confirmed D+HUS (all P < .05).

Conclusions

Polymorphisms in many non-complement-related genes may contribute to D+HUS susceptibility. These results require replication, but they suggest novel therapeutic targets in patients with D+HUS.

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.

Recovery from mild Escherichia coli O157:H7 infection in young and aged C57BL/6 mice with intact flora estimated by fecal shedding, locomotor activity and grip strength

Escherichia coli 0157:H7 is a food-borne pathogen that can cause severe complications in vulnerable populations. Mouse infection models of E. coli 0157:H7 are usually developed under severe animal suffering classification by depleting the normal flora, in which age plays a role.

OBJECTIVE

To develop a refined method for longitudinal monitoring of E. coli 0157:H7 in young and old mice with intact flora.

METHODS

We applied discriminant analysis and computed composite standardized scores from 19 variables obtained from physiological parameters, analysis of locomotor activity, grip strength measurement and fecal shedding in 16 aged and 16 young C57BL/6 mice after two mild oral challenges of E. coli 0157:H7. The resulting scores were validated in another experiment performed in 24 aged and 24 young mice including a group (8 aged and 8 young mice) treated with oxytetracycline.

RESULTS

We show that our scores are significantly affected in the post-infection period and that can be used to measure and compare the recovery time after a treatment. The scores are most sensitive when separately developed in young and aged mice.

CONCLUSIONS

We developed a method that minimizes the level of animal suffering and that can be applied in preclinical testing of new therapies.

Anti-tumor activity of Escherichia coli Shiga toxin A subunit delivered by SF9 insect cells

Cancer remains a major health problem around the world. A Shiga toxin is a bacterial toxin often produced by Shigella dysenteriae and Escherichia coli. A subunit of the Shiga toxin (StxA) is a cytotoxic agent which could be used to induce death in cancer cells. StxA expressed from baculovirus was evaluated in a pTriEx™ expression vector. The baculovirus vector was used for the A subunit delivery of StxA. StxA cell cytotoxicity was induced by the virus and assessed in the MCF7 and HeLa cell lines. In addition, the breast cancer cytotoxicity of the expressed StxA was also assessed in a cancer induced in mice. The cytotoxicity of the recombinant StxA baculovirus with different multiplicities of infection (MOI) was measured. The results showed that significant cytotoxicity can be induced on the mammalian epithelial breast cancer cell lines, MCF7 and HeLa cells with MOI ≥ 2. The results also showed that a malignant tumor induced by MCF7 could be inhibited in a mouse cancer model. Therefore, it can be concluded that StxA, expressed by baculovirus, could be used for in vitro and in vivo gene delivery. In this study StxA, delivered by the baculovirus inhibited cell proliferation, and eliminated HeLa and MCF7 cells, in vitro. In conclusion, this method can be used as a safe alternative for anticancer drug delivery inside cancer cells.

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.

Lethality Prediction for Escherichia Coli O157:H7 and Uropathogenic E. coli in Ground Chicken Treated with High Pressure Processing and Trans-Cinnamaldehyde

Pathogenic Escherichia coli, intestinal (O157:H7) as well as extraintestinal types (for example, Uropathogenic E. coli [UPEC]) are commonly found in many foods including raw chicken meat. The resistance of E. coli O157:H7 to UPEC in chicken meat under the stresses of high hydrostatic Pressure (HHP, also known as HPP-high pressure processing) and trans-cinnamaldehyde (an essential oil) was investigated and compared. UPEC was found slightly less resistant than O157:H7 in our test parameter ranges. With the addition of trans-cinnamaldehyde as an antimicrobial to meat, HPP lethality enhanced both O157:H7 and UPEC inactivation. To facilitate the predictive model development, a central composite design (CCD) was used to assess the 3-parameter effects, that is, pressure (300 to 400 MPa), trans-cinnamaldehyde dose (0.2 to 0.5%, w/w), and pressure-holding time (15 to 25 min), on the inactivation of E. coli O157:H7 and UPEC in ground chicken. Linear models were developed to estimate the lethality of E. coli O157:H7 (R² = 0.86) and UPEC (R² = 0.85), as well as dimensionless nonlinear models. All models were validated with data obtained from separated CCD combinations. Because linear models of O157:H7 and UPEC had similar R² and the significant lethality difference of CCD points was only 9 in 20; all data were combined to generate models to include both O157:H7 and UPEC. The results provide useful information/tool to predict how pathogenic E. coli may survive HPP in the presence of trans-cinnamaldehyde and to achieve a great than 5 log CFU/g reduction in chicken meat. The models may be used for process optimization, product development and to assist the microbial risk assessment.

PRACTICAL APPLICATION

The study provided an effective means to reduce the high hydrostatic pressure level with incorporation of antimicrobial compound to achieve a 5-log reduction of pathogenic E. coli without damaging the raw meat quality. The developed models may be used to predict the high pressure processing lethality (and process optimization), product development (ingredient selection), and to assist the microbial risk assessment.

Shiga Toxin Glycosphingolipid Receptors in Human Caco-2 and HCT-8 Colon Epithelial Cell Lines

Shiga toxins (Stxs) released by enterohemorrhagic Escherichia coli (EHEC) into the human colon are the causative agents for fatal outcome of EHEC infections. Colon epithelial Caco-2 and HCT-8 cells are widely used for investigating Stx-mediated intestinal cytotoxicity. Only limited data are available regarding precise structures of their Stx receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer), and lipid raft association. In this study we identified Gb3Cer and Gb4Cer lipoforms of serum-free cultivated Caco-2 and HCT-8 cells, chiefly harboring ceramide moieties composed of sphingosine (d18:1) and C16:0, C22:0 or C24:0/C24:1 fatty acid. The most significant difference between the two cell lines was the prevalence of Gb3Cer with C16 fatty acid in HCT-8 and Gb4Cer with C22–C24 fatty acids in Caco-2 cells. Lipid compositional analysis of detergent-resistant membranes (DRMs), which were used as lipid raft-equivalents, indicated slightly higher relative content of Stx receptor Gb3Cer in DRMs of HCT-8 cells when compared to Caco-2 cells. Cytotoxicity assays revealed substantial sensitivity towards Stx2a for both cell lines, evidencing little higher susceptibility of Caco-2 cells versus HCT-8 cells. Collectively, Caco-2 and HCT-8 cells express a plethora of different receptor lipoforms and are susceptible towards Stx2a exhibiting somewhat lower sensitivity when compared to Vero cells.

Updated Insight into the Physiological and Pathological Roles of the Retromer Complex

Retromer complexes mediate protein trafficking from the endosomes to the trans-Golgi network (TGN) or through direct recycling to the plasma membrane. In yeast, they consist of a conserved trimer of the cargo selective complex (CSC), Vps26-Vps35-Vps29 and a dimer of sorting nexins (SNXs), Vps5-Vps17. In mammals, the CSC interacts with different kinds of SNX proteins in addition to the mammalian homologues of Vps5 and Vps17, which further diversifies retromer functions. The retromer complex plays important roles in many cellular processes including restriction of invading pathogens. In this review, we summarize some recent developments in our understanding of the physiological and pathological functions of the retromer complex.