AB5 Enterotoxin-Mediated Pathogenesis: Perspectives Gleaned from Shiga Toxins.

Foodborne diseases affect an estimated 600 million people worldwide annually, with the majority of these illnesses caused by Norovirus, Vibrio, Listeria, Campylobacter, Salmonella, and Escherichia coli. To elicit infections in humans, bacterial pathogens express a combination of virulence factors and toxins. AB5 toxins are an example of such toxins that can cause various clinical manifestations, including dehydration, diarrhea, kidney damage, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). Treatment of most bacterial foodborne illnesses consists of fluid replacement and antibiotics. However, antibiotics are not recommended for infections caused by Shiga toxin-producing E. coli (STEC) because of the increased risk of HUS development, although there are conflicting views and results in this regard. Lack of effective treatment strategies for STEC infections pose a public health threat during outbreaks; therefore, the debate on antibiotic use for STEC infections could be further explored, along with investigations into antibiotic alternatives. The overall goal of this review is to provide a succinct summary on the mechanisms of action and the pathogenesis of AB5 and related toxins, as expressed by bacterial foodborne pathogens, with a primary focus on Shiga toxins (Stx). The role of Stx in human STEC disease, detection methodologies, and available treatment options are also briefly discussed.

Eimeria pragensis infection alters the gut microenvironment to favor extrinsic shiga toxin-producing Escherichia coli O157:H7 colonization in mice.

We examined the effects of Eimeria pragensis infection on intestinal peristalsis, goblet cell proliferation and intestinal flora in C57BL/6 mice. Intestinal peristalsis was evaluated by radiography using barium at 7 days post-infection (p.i.). The intestinal peristalsis of E. pragensis-infected mice was significantly suppressed compared with uninfected control mice. Twenty-three mice were divided into 5 groups of 4 or 5 mice each; 2 groups of mice were infected with E. pragensis and the others were kept uninfected. At 7 days p.i., E. pragensis-infected and -uninfected mice were sacrificed to examine goblet cell numbers in the intestines, and significant decreases were observed only in the infected mice. Shiga toxin-producing Escherichia coli (STEC) O157:H7 was inoculated orally in mice both infected and uninfected with E. pragensis at 7 days p.i., with the remaining mice used as uninoculated controls. When mice were sacrificed at 2 days after STEC inoculation, STEC was only detected in the intestines of E. pragensis-infected mice. Colonization of STEC was also confirmed by immunohistochemistry on the surface of epithelial cells in concurrently infected/inoculated mice. Also, an overgrowth of residential E. coli was observed only in E. pragensis-infected mice. These results suggest that E. pragensis induces the suppression of intestinal peristalsis and modifies the intestinal environment to facilitate artificially introduced STEC colonization and multiplication, in addition to residential E. coli overgrowth.

Gut-Kidney Axis on Chip for Studying Effects of Antibiotics on Risk of Hemolytic Uremic Syndrome by Shiga Toxin-Producing Escherichia coli.

Shiga toxin-producing Escherichia coli (STEC) infects humans by colonizing the large intestine, and causes kidney damage by secreting Shiga toxins (Stxs). The increased secretion of Shiga toxin 2 (Stx2) by some antibiotics, such as ciprofloxacin (CIP), increases the risk of hemolytic-uremic syndrome (HUS), which can be life-threatening. However, previous studies evaluating this relationship have been conflicting, owing to the low frequency of EHEC infection, very small number of patients, and lack of an appropriate animal model. In this study, we developed gut-kidney axis (GKA) on chip for co-culturing gut (Caco-2) and kidney (HKC-8) cells, and observed both STEC O157:H7 (O157) infection and Stx intoxication in the gut and kidney cells on the chip, respectively. Without any antibiotic treatment, O157 killed both gut and kidney cells in GKA on the chip. CIP treatment reduced O157 infection in the gut cells, but increased Stx2-induced damage in the kidney cells, whereas the gentamycin treatment reduced both O157 infection in the gut cells and Stx2-induced damage in the kidney cells. This is the first report to recapitulate a clinically relevant situation, i.e., that CIP treatment causes more damage than gentamicin treatment. These results suggest that GKA on chip is very useful for simultaneous observation of O157 infections and Stx2 poisoning in gut and kidney cells, making it suitable for studying the effects of antibiotics on the risk of HUS.

A Validation System for Selection of Bacteriophages against Shiga Toxin-Producing Escherichia coli Contamination.

Shiga toxin-producing Escherichia coli (STEC) can cause severe infections in humans, leading to serious diseases and dangerous complications, such as hemolytic-uremic syndrome. Although cattle are a major reservoir of STEC, the most commonly occurring source of human infections are food products (e.g., vegetables) contaminated with cow feces (often due to the use of natural fertilizers in agriculture). Since the use of antibiotics against STEC is controversial, other methods for protection of food against contaminations by these bacteria are required. Here, we propose a validation system for selection of bacteriophages against STEC contamination. As a model system, we have employed a STEC-specific bacteriophage vB_Eco4M-7 and the E. coli O157:H7 strain no. 86-24, bearing Shiga toxin-converting prophage ST2-8624 (Δstx2::cat gfp). When these bacteria were administered on the surface of sliced cucumber (as a model vegetable), significant decrease in number viable E. coli cells was observed after 6 h of incubation. No toxicity of vB_Eco4M-7 against mammalian cells (using the Balb/3T3 cell line as a model) was detected. A rapid decrease of optical density of STEC culture was demonstrated following addition of a vB_Eco4M-7 lysate. However, longer incubation of susceptible bacteria with this bacteriophage resulted in the appearance of phage-resistant cells which predominated in the culture after 24 h incubation. Interestingly, efficiency of selection of bacteria resistant to vB_Eco4M-7 was higher at higher multiplicity of infection (MOI); the highest efficiency was evident at MOI 10, while the lowest occurred at MOI 0.001. A similar phenomenon of selection of the phage-resistant bacteria was also observed in the experiment with the STEC-contaminated cucumber after 24 h incubation with phage lysate. On the other hand, bacteriophage vB_Eco4M-7 could efficiently develop in host bacterial cells, giving plaques at similar efficiency of plating at 37, 25 and 12 °C, indicating that it can destroy STEC cells at the range of temperatures commonly used for vegetable short-term storage. These results indicate that bacteriophage vB_Eco4M-7 may be considered for its use in food protection against STEC contamination; however, caution should be taken due to the phenomenon of the appearance of phage-resistant bacteria.

Functional Analysis of Shiga Toxin-Producing Escherichia coli Biofilm Components in Plant Leaves.

Plants represent alternative or secondary hosts for Shiga toxin-producing Escherichia coli (STEC), enabling transmission of the pathogens through the food chain on horticultural crops. This becomes a public health concern for plants that are eaten raw or minimally processed, such as leafy salad and fruits. STEC actively interact with plants as hosts, and so to determine the mechanistic basis to the interaction, it is necessary to assess STEC gene function in planta. Here, we describe analysis of an STEC biofilm component, curli, that plays a role in STEC colony formation in plant leaves. It also serves as a suitable example of the approaches required for qualitative and quantitative assessment of functional host colonization traits.

Human Epithelial Stem Cell-Derived Colonoid Monolayers as a Model to Study Shiga Toxin-Producing Escherichia coli-Host Interactions.

Human intestinal organoid cultures established from crypt-derived stem cells truly revolutionized our approach to study intestinal epithelial physiology and pathologies as they can be propagated indefinitely and preserve the genetic signature of the donor and the gut segment specificity in culture. Here we describe human stem cell-derived colonoid monolayers as a reliable and reproducible model to study Shiga toxin-producing Escherichia coli (STEC) infection and STEC-caused pathologies of the whole colonic epithelium comprising a mixture of colonocytes, goblet, enteroendocrine, and other rare cells present in human colonic epithelial tissue.

Extracellular Vesicles and Renal Endothelial Cells: A Fatal Attraction in Hemolytic Uremic Syndrome.

This review focuses on typical hemolytic uremic syndrome (HUS), a life-threatening sequela of human infections caused, particularly in children, by Shiga toxin-producing Escherichia coli strains. Thrombotic microangiopathy of the brain and the kidney is the end point of toxin action, resulting in the hallmarks of HUS (ie, thrombocytopenia, anemia, and acute renal failure). A growing body of evidence points to the role of extracellular vesicles released in the blood of patients by toxin-challenged circulating cells (monocytes, neutrophils, and erythrocytes) and platelets, as a key factor in the pathogenesis of HUS. This review provides i) an updated description of the pathogenesis of Shiga toxin-producing E. coli infections; ii) an analysis of blood cell-derived extracellular vesicles, and of their parent cells, as triggering factors in HUS; and iii) a model explaining why Shiga toxin-containing vesicles dock preferentially to the endothelia of target organs.

Transmission Dynamics of Shiga Toxin-Producing Escherichia coli in New Zealand Cattle from Farm to Slaughter.

Cattle are asymptomatic carriers of Shiga toxin-producing Escherichiacoli (STEC) strains that can cause serious illness or death in humans. In New Zealand, contact with cattle feces and living near cattle populations are known risk factors for human STEC infection. Contamination of fresh meat with STEC strains also leads to the potential for rejection of consignments by importing countries. We used a combination of PCR/matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) and whole-genome sequencing (WGS) to evaluate the presence and transmission of STEC on farms and in processing plants to better understand the potential pathways for human exposure and thus mitigate risk. Animal and environmental samples (n = 2,580) were collected from six farms and three meat processing plants in New Zealand during multiple sampling sessions in spring of 2015 and 2016. PCR/MALDI-TOF analysis revealed that 6.2% were positive for "Top 7" STEC. Top 7 STEC strains were identified in all sample sources (n = 17) tested. A marked increase in Top 7 STEC prevalence was observed between calf hides on farm (6.3% prevalence) and calf hides at processing plants (25.1% prevalence). Whole-genome sequencing was performed on Top 7 STEC bacterial isolates (n = 40). Analysis of STEC O26 (n = 25 isolates) revealed relatively low genetic diversity on individual farms, consistent with the presence of a resident strain disseminated within the farm environment. Public health efforts should focus on minimizing human contact with fecal material on farms and during handling, transport, and slaughter of calves. Meat processing plants should focus on minimizing cross-contamination between the hides of calves in a cohort during transport, lairage, and slaughter.IMPORTANCE Cattle are asymptomatic carriers of Shiga toxin-producing E. coli (STEC) strains, which can cause serious illness or death in humans. Contact with cattle feces and living near cattle are known risk factors for human STEC infection. This study evaluated STEC carriage in young calves and the farm environment with an in-depth evaluation of six farms and three meat processing plants over 2 years. An advanced molecular detection method and whole-genome sequencing were used to provide a detailed evaluation of the transmission of STEC both within and between farms. The study revealed widespread STEC contamination within the farm environment, but no evidence of recent spread between farms. Contamination of young dairy calf hides increased following transport and holding at meat processing plants. The elimination of STEC in farm environments may be very difficult given the multiple transmission routes; interventions should be targeted at decreasing fecal contamination of calf hides during transport, lairage, and processing.

Use of Fimbrial Rod for F18ab Fimbriae+ STEC Colonization to Host Cells.

Type 1 fimbriae are important virulence determinants of some Gram-negative pathogens, which promote bacterial colonization. The fimbrial rod is primarily composed of multiple copies of the major fimbrial subunit FimA. FimH adhesin, however, is present as a fibrillar tip structure that drive bacteria binding to host cellular mannose containing receptor. Here, we provide protocols to evaluate and compare the function of type 1 fimbrial subunits in F18ab fimbriae+ Shiga toxin-producing Escherichia coli (STEC). We found that both FimA and FimH are required for bacterial adhesion, invasion, and biofilm formation. Deleting fimA gene showed much more reduction in bacterial adhesion and invasion to porcine intestinal columnar epithelial cells IPEC-J2, than that of fimH mutant. Biofilm formation was significantly reduced in both mutants with an equal level. In addition, qPCR demonstrated that either fimA or fimH deletion down-regulated the bacterial flagella and F18 fimbriae genes expression, while up-regulated adhesin was involved in diffuse adherence-I (AIDA-I) gene expression, suggesting the co-regulation of cell surface-localized adhesins in F18ab fimbriae+ STEC.

Seasonal Prevalence of Shiga Toxin-Producing Escherichia coli on Pork Carcasses for Three Steps of the Harvest Process at Two Commercial Processing Plants in the United States.

Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen that has a significant impact on public health, with strains possessing the attachment factor intimin referred to as enterohemorrhagic E. coli (EHEC) and associated with life-threatening illnesses. Cattle and beef are considered typical sources of STEC, but their presence in pork products is a growing concern. Therefore, carcasses (n = 1,536) at two U.S. pork processors were sampled once per season at three stages of harvest (poststunning skins, postscald carcasses, and chilled carcasses) and then examined using PCR for Shiga toxin genes (stx), intimin genes (eae), aerobic plate count (APC), and Enterobacteriaceae counts (EBC). The prevalence of stx on skins, postscald, and chilled carcasses was 85.3, 17.5, and 5.4%, respectively, with 82.3, 7.8, and 1.7% of swabs, respectively, having stx and eae present. All stx-positive samples were subjected to culture isolation that resulted in 368 STEC and 46 EHEC isolates. The most frequently identified STEC were serogroups O121, O8, and O91 (63, 6.7, and 6.0% of total STEC, respectively). The most frequently isolated EHEC was serotype O157:H7 (63% of total EHEC). Results showed that scalding significantly reduced (P < 0.05) carcass APC and EBC by 3.00- and 2.50-log10 CFU/100 cm2, respectively. A seasonal effect was observed, with STEC prevalence lower (P < 0.05) in winter. The data from this study show significant (P < 0.05) reduction in the incidence of STEC (stx) from 85.3% to 5.4% and of EHEC (stx plus eae) from 82.3% to 1.7% within the slaughter-to-chilling continuum, respectively, and that potential EHEC can be confirmed present throughout using culture isolation.IMPORTANCE Seven serogroups of STEC are responsible for most (>75%) cases of severe illnesses caused by STEC and are considered adulterants of beef. However, some STEC outbreaks have been attributed to pork products, although the same E. coli are not considered adulterants in pork because little is known of their prevalence along the pork chain. The significance of the work presented here is that it identifies disease-causing STEC, EHEC, demonstrating that these same organisms are a food safety hazard in pork as well as beef. The results show that most STEC isolated from pork are not likely to cause severe disease in humans and that processes used in pork harvest, such as scalding, offer a significant control point to reduce contamination. The results will assist the pork processing industry and regulatory agencies to optimize interventions to improve the safety of pork products.

Bacteriophage biocontrol of Shiga toxigenic Escherichia coli (STEC) O145 biofilms on stainless steel reduces the contamination of beef.

Shiga toxigenic Escherichia coli (STEC) can form biofilms and frequently cause serious foodborne illnesses. A strain of STEC O145:H25 (EC19990166) known to be a strong biofilm former was used to evaluate the efficacy of bacteriophage AZO145A against biofilms formed on stainless steel (SS) coupons. Exposure of STEC O145:H25 to phage AZO145A (1010 PFU/mL) for 2 h resulted in a 4.0 log10 reduction (P < 0.01) of planktonic cells grown in M9 broth at 24 °C for 24 h, while reductions were 2.0 log10 CFU/mL if these cells were grown for 48 h or 72 h prior to phage treatment. STEC O145 biofilms formed on SS coupons for 24, 48 and 72 h were reduced (P < 0.01) 2.9, 1.9 and 1.9 log10 CFU/coupon by phages. STEC O145 cells in biofilms were readily transferred from the surface of the SS coupon to beef (3.6 log10 CFU/coupon) even with as little as 10 s of contact with the meat surface. However, transfer of STEC O145 cells from biofilms that formed on SS coupons for 48 h to beef was reduced (P < 0.01) by 3.1 log10 CFU by phage (2 × 1010 PFU/mL) at 24 °C. Scanning electron microscopy revealed that bacterial cells within indentations on the surface of SS coupons were reduced by phage. These results suggest that bacteriophage AZO145A could be effective in reducing the viability of biofilm-adherent STEC O145 on stainless steel in food industry environments.

Genetic and Phenotypic Factors Associated with Persistent Shedding of Shiga Toxin-Producing Escherichia coli by Beef Cattle.

Shiga toxin-producing Escherichia coli (STEC) is a leading cause of foodborne infections. Cattle are an important STEC reservoir, although little is known about specific pathogen traits that impact persistence in the farm environment. Hence, we sought to evaluate STEC isolates recovered from beef cattle in a single herd in Michigan. To do this, we collected fecal grabs from 26 cattle and resampled 13 of these animals at 3 additional visits over a 3-month period. In all, 66 STEC isolates were recovered for genomics and biofilm quantification using crystal violet assays. The STEC population was diverse, representing seven serotypes, including O157:H7, O26:H11, and O103:H2, which are commonly associated with human infections. Although a core genome analysis of 2,933 genes grouped isolates into clusters based on serogroups, some isolates within each cluster had variable biofilm levels and virulence gene profiles. Most (77.8%; n = 49) isolates harbored stx2a, while 38 (57.5%) isolates formed strong biofilms. Isolates belonging to the predominant serogroup O6 (n = 36; 54.5%) were more likely to form strong biofilms, persistently colonize multiple cattle, and be acquired over time. A high-quality single nucleotide polymorphism (SNP) analysis of 33 O6 isolates detected between 0 and 13 single nucleotide polymorphism (SNP) differences between strains, indicating that highly similar strain types were persisting in this herd. Similar findings were observed for other persistent serogroups, although key genes were found to differ among strong and weak biofilm producers. Together, these data highlight the diversity and persistent nature of some STEC types in this important food animal reservoir.IMPORTANCE Food animal reservoirs contribute to Shiga toxin-producing Escherichia coli (STEC) evolution via the acquisition of horizontally acquired elements like Shiga toxin bacteriophages that enhance pathogenicity. In cattle, persistent fecal shedding of STEC contributes to contamination of beef and dairy products and to crops being exposed to contaminated water systems. Hence, identifying factors important for STEC persistence is critical. This longitudinal study enhances our understanding of the genetic diversity of STEC types circulating in a cattle herd and identifies genotypic and phenotypic traits associated with persistence. Key findings demonstrate that multiple STEC types readily persist in and are transmitted across cattle in a shared environment. These dynamics also enhance the persistence of virulence genes that can be transferred between bacterial hosts, resulting in the emergence of novel STEC strain types. Understanding how pathogens persist and diversify in reservoirs is important for guiding new preharvest prevention strategies aimed at reducing foodborne transmission to humans.

The gut microbes, Enterococcus and Escherichia-Shigella, affect the responses of heart valve replacement patients to the anticoagulant warfarin.

Numerous algorithms based on patient genetic variants have been established with the aim of reducing the risk of GI bleeding and thromboembolism during warfarin administration. However, approximately 35 % of individual warfarin sensitivity still remains unexplained. Few of warfarin algorithms take into account gut microbiota profiles. The identification of certain microbiome will provide new targets and new strategies for reducing the risk of bleeding and thromboembolism during warfarin administration. In this study, we collected plasma and stool samples from 200 inpatients undergoing heart valve replacement (HVR), which were classified as low responder (LR), high responder (HR) and normal responder (NR). Significant differences were observed in the diversity and relative abundance of the gut microbiota among the three groups. The genus Escherichia-Shigella was enriched significantly in the LRs (P = 3.189e-11), while the genus Enterococcus was enriched significantly in the HRs (P = 1.249e-11). The amount of VK2 synthesized by gut microbiota in LR group was much higher than that in HR group (P = 0.005). Whole genome shotgun sequencing indicated that the relative abundance of enzymes and modules associated with VK biosynthesis was significantly higher in LRs than in HRs or NRs. The 12 microbial markers were identified through tenfold cross-validation with a random forest model. The results provided a new microbial diagnostic model that can be used to inform modulation of warfarin dosage on the basis of patient intestinal flora composition.

Combination of organic acids and low-dose gamma irradiation as antimicrobial treatment to inactivate Shiga toxin-producing Escherichia coli inoculated in beef trimmings: Lack of benefits in relation to single treatments.

The aim of this study was to assess the efficacy of lactic acid (LA), caprylic acid (CA), high- (HDI) and low- (LDI) dose gamma irradiation and LDI combined with LA or CA on the inactivation of a pool of Shiga toxin-producing Escherichia coli (STEC) strains inoculated on beef trimmings. The three most efficacious treatments were selected to study their effect on meat quality parameters and sensory attributes. The inoculum included five native STEC serogroups (O26, O103, O111, O145 and O157). The treatments applied were 0.5% LA, 0.04% CA, 0.5 kGy LDI, 2 kGy HDI, LDI+LA and LDI+CA. Beef trimmings were divided into two groups; one was inoculated with high (7 log CFU/g) and the other with low (1 log CFU/g) level of inoculum. Efficacy was assessed by estimating log reduction and reduction of stx- and eae-positive samples after enrichment, respectively. Results showed that treatments with organic acids alone were not effective in reducing STEC populations. For high inoculum samples, the most effective treatment was HDI followed by LDI+LA and LDI alone or combined with CA. For low inoculum samples, the most effective treatment was HDI followed by LDI alone or combined with organic acids. Concerning meat quality parameters and sensory attributes, irradiation treatments (LDI and HDI) caused minimal changes, while LDI+LA modified them significantly compared with the control. Therefore, based on our results, no benefits were observed after combining organic acids with gamma irradiation.

Biofilm formation by South African non-O157 Shiga toxigenic Escherichia coli on stainless steel coupons.

This study examined the biofilm-forming ability of six non-O157 Shiga-toxin-producing Escherichia coli (STEC) strains: O116:H21, wzx-Onovel5:H19, O129:H21, O129:H23, O26:H11, and O154:H10 on stainless steel coupons after 24, 48, and 72 h of incubation at 22 °C and after 168 h at 10 °C. The results of crystal violet staining revealed that strains O129:H23 and O154:H10 were able to form biofilms on both the submerged surface and the air-liquid interface of coupons, whereas strains O116:H21, wzx-Onovel5:H19, O129:H21, and O26:H11 formed biofilm only at the air-liquid interface. Viable cell counts and scanning electron microscopy showed that biofilm formation increased (p < 0.05) over time. The biofilm-forming ability of non-O157 STEC was strongest (p < 0.05) at 22 °C after 48 h of incubation. The strongest biofilm former regardless of temperature was O129:H23. Generally, at 10 °C, weak to no biofilm was observed for isolates O154:H10, O116:H21, wzx-Onovel5:H19, O26:H11, and O129:H21 after 168 h. This study found that temperature affected the biofilm-forming ability of non-O157 STEC strains. Overall, our data indicate a high potential for biofilm formation by the isolates at 22 °C, suggesting that non-O157 STEC strains could colonize stainless steel within food-processing facilities. This could serve as a potential source of adulteration and promote the dissemination of these potential pathogens in food.

Heme as Possible Contributing Factor in the Evolvement of Shiga-Toxin Escherichia coli Induced Hemolytic-Uremic Syndrome.

Shiga-toxin (Stx)-producing Escherichia coli hemolytic-uremic syndrome (STEC-HUS) is one of the most common causes of acute kidney injury in children. Stx-mediated endothelial injury initiates the cascade leading to thrombotic microangiopathy (TMA), still the exact pathogenesis remains elusive. Interestingly, there is wide variability in clinical presentation and outcome. One explanation for this could be the enhancement of TMA through other factors. We hypothesize that heme, as released during extensive hemolysis, contributes to the etiology of TMA. Plasma levels of heme and its scavenger hemopexin and degrading enzyme heme-oxygenase-1 (HO-1) were measured in 48 STEC-HUS patients. Subsequently, the effect of these disease-specific heme concentrations, in combination with Stx, was assessed on primary human glomerular microvascular endothelial cells (HGMVECs). Significantly elevated plasma heme levels up to 21.2 µM were found in STEC-HUS patients compared to controls and were inversely correlated with low or depleted plasma hemopexin levels (R2 -0.74). Plasma levels of HO-1 are significantly elevated compared to controls. Interestingly, especially patients with high heme levels (n = 12, heme levels above 75 quartile range) had high plasma HO-1 levels with median of 332.5 (86-720) ng/ml (p = 0.008). Furthermore, heme is internalized leading to a significant increase in reactive oxygen species production and stimulated both nuclear translocation of NF-κB and increased levels of its target gene (tissue factor). In conclusion, we are the first to show elevated heme levels in patients with STEC-HUS. These increased heme levels mediate endothelial injury by promoting oxidative stress and a pro-inflammatory and pro-thrombotic state. Hence, heme may be a contributing and driving factor in the pathogenesis of STEC-HUS and could potentially amplify the cascade leading to TMA.

Effects of Beef Juice on Biofilm Formation by Shiga Toxin-Producing Escherichia coli on Stainless Steel.

Shiga toxin-producing Escherichia coli (STEC) are a leading cause of foodborne illnesses worldwide, with beef and beef products as a common food reservoir. STEC strains may be present in beef-processing environments in the form of biofilms. The exudate of raw beef, also referred to as beef juice, has been identified as an important source of bacterial contamination on food-processing surfaces. This study applied beef juice as a food-based model to study its effects on biofilm formation of six STEC isolates on stainless steel. Crystal violet staining and cell enumeration demonstrated that beef juice inhibited the biofilm formation of strains O113, O145, and O91 up to 24 h at 22°C, but that biofilm increased (p < 0.05) thereafter over 72 h. Biofilms formed by O157, O111, and O45 were not affected by the addition of beef juice over the whole incubation period. Electron microscopy showed that the morphology of biofilm cells was altered and more extracellular matrix was produced with beef juice than with M9 medium. The present study demonstrated that beef juice residues on stainless steel can enhance biofilm formation of some STEC strains. Thorough and frequent cleaning of meat residues and exudate during meat production and handling is critical to reduce STEC biofilm formation even at 13°C.

Particulate Shiga Toxin 2 in Blood is Associated to the Development of Hemolytic Uremic Syndrome in Children.

Hemolytic uremic syndrome (HUS), the leading cause of acute renal failure in children (< 3 years), is mainly related to Shiga toxins (Stx)-producing Escherichia coli (STEC) infections. STEC are confined to the gut resulting in hemorrhagic colitis, whereas Stx are delivered in blood to target kidney and brain, with unclear mechanisms, triggering HUS in 5 to 15% of infected children. Stx were found on circulating cells, free in sera (soluble Stx) or in blood cell-derived microvesicles (particulate Stx), whereby the relationship between these forms of circulating toxins is unclear. Here, we have examined 2,846 children with bloody diarrhea and found evidence of STEC infection in 5%. Twenty patients were enrolled to study the natural course of STEC infections before the onset of HUS. In patients, Stx were found to be associated to circulating cells and/or free and functionally active in sera. In most children, Stx were bound to neutrophils when high amounts of toxins were found in feces. Time-course analysis showed that Stx increased transiently in patients' sera while the decrease of toxin amount on leukocytes was observed. Notably, patients who recovered (85%) displayed different settings than those who developed HUS (15%). The distinctive feature of the latter group was the presence in blood of particulate Stx2 (Stx2 sedimented at g-forces corresponding to 1 µm microvesicles) the day before diagnosis of HUS, during the release phase of toxins from circulating cells. This observation strongly suggests the involvement of blood cell-derived particulate Stx2 in the transition from hemorrhagic colitis to HUS.

Shiga toxin-producing Escherichia coli (STEC) shedding in a wild roe deer population.

Worldwide infections by Shiga toxin-producing Escherichia coli (STEC) in humans have been reported after consumption of mainly beef, but also deer meat. Not only the consumption of contaminated deer meat represents a risk, but also the transmission of STEC between deer and domestic animals should be considered. Within the framework of a telemetry study of roe deer (Capreolus capreolus) the aim was to analyse the occurrence of STEC. Due to the chance to sample some animals several times it was possible to obtain data on the repeated shedding of STEC in roe deer. In total 124 faeces or rectal swabs of 77 live trapped roe deer were collected. The isolates obtained were characterized for stx subtypes, different virulence genes, the so-called top-five serogroups, phylogenetic groups, PFGE-types and antimicrobial susceptibilities. The majority of roe deer were stx-positive whenever sampled. Twenty-eight animals were sampled more than once and were used to examine the duration of shedding STEC. The time interval of 6 persistently stx-negative tested animals was between 6 and 440d (median 49d, interquartile range (IQR) 17-258d). Ten animals excreted undistinguishable STEC strains in intervals between 4 and 778d (median 42d, IQR 22-79d). Most of the isolates were stx2b-positive, eae-negative and frequently ehlyA-positive. None of the isolates belonged to serogroup O26, O103, O111, O145 and O157, respectively. All isolates were sensitive to the antimicrobial substances tested. Although the duration of each shedding event could not be determined the results indicate long-term excretion of STEC in roe deer. This is an important consideration for the observance of good hygiene practice while field dressing of deer and preparing deer meat.

Efectos del medio de cultivo y de la metodología aplicada sobre la formación de biopelículas de 2 cepas de Escherichia coli diarreagénicas / Effects of the culture medium and the methodology applied on the biofilm formation of 2 diarrheagenic Escherichia coli strains

La capacidad de formar biopelículas de los microorganismos patógenos en gran variedad de ambientes, superficies y condiciones trae consigo un importante riesgo, tanto para la industria alimentaria como para la salud pública. Este trabajo tuvo como objetivo evaluar y comparar los efectos de la metodología empleada y de los medios de cultivo utilizados, sobre la capacidad de una cepa de Escherichia coli verotoxigénica no O157 y una enteropatogénica de formar biopelículas sobre una superficie de poliestireno. Se ensayaron 2 variantes metodológicas en cultivo estático y se utilizaron medios de cultivo con diferente composición. Los resultados mostraron que ambas cepas formaron una mayor cantidad de biopelícula en cultivo en LB suplementado con glucosa, con recambio del medio a las 24 h y la cuantificación de la biopelícula realizada a las 48 h de incubación. Dichas condiciones podrían ser utilizadas en futuros estudios sobre formación de biopelícula.

The ability to form biofilms of pathogenic microorganisms in a wide variety of environments, surfaces and conditions constitute an important risk, both for the food industry and for public health. The aim of this work was to evaluate and to compare the effects of the methodology applied and the culture medium used on the ability of a non-O157 verotoxigenic Escherichia coli strain and an enteropathogenic strain to form biofilm on polystyrene surface. Two methodological variants were tested in static culture and culture mediums with different composition were used. The results showed that both strains were able to form a greater biofilm under culture in LB supplemented with glucose, with medium replacement at 24 h and the quantification of the biofilm carried out at 48 h of incubation. These conditions could be used in future studies on biofilm formation.