A review of factors that affect transmission and survival of verocytotoxigenic Escherichia coli in the European farm to fork beef chain

How to Improve Surveillance Program for Shiga Toxin-Producing E. coli (STEC): Gap Analysis and Pilot Study

Several pathotypes of enteric E. coli have been identified. The group represented by Shiga toxin-producing E. coli (STEC) is of particular interest. Raw milk and raw milk products are significant sources of STEC infection in humans; therefore, identifying pathogens at the herd level is crucial for public health. Most national surveillance programs focus solely on raw milk and raw milk cheeses that are ready for retail sale, neglecting the possibility of evaluating the source of contamination directly at the beginning of the dairy chain. To assess the viability of the application of new molecular methodologies to STEC identification in raw milk filters and in calf feces, we analyzed 290 samples from 18 different dairy herds, including 88 bulk tank milk (BTM), 104 raw milk filters (RMF), and 98 calf feces samples. In total 3.4% of BTM, 41.4% of RMF, and 73.4% of calves' feces were positive for stx, supporting our hypothesis that BTM is not a suitable matrix to assess the presence of STEC at herd level, underestimating it. Our conclusion is that the surveillance program needs critical and extensive improvements such as RMF and calves' feces analysis implementation to be more efficient in detecting and preventing STEC infections. The epidemiology of these infections and the characteristics of the pathogen clearly show how a One Health approach will be pivotal in improving our capabilities to control the spread of these infections.

Droplet Digital PCR (ddPCR) Analysis for Detecting Shiga-Toxin-Producing Escherichia coli (STEC)

Verocytotoxin-producing Escherichia coli, also referred to as Shiga-toxin-producing Escherichia coli (STEC), can be transmitted to humans through person-to-person contact, consumption of contaminated food or water, or by direct contact with animals. Its clinical and economic consequences have prompted the development of alternative approaches to the official method of analysis “UNI CEN ISO/TS 13136: 2012”, which describes the identification of STEC through the detection of its main virulence genes. Recently, droplet digital PCR (ddPCR) has been proposed as a technique for the sequence-specific detection and direct quantification of nucleic acids. The present study aimed to investigate if ddPCR could be able to detect STEC in less time than that required by the official method. This study consisted of the ddPCR of slices of beef contaminated with STEC and of the sponges used for beef official control at the slaughter stage. The results showed the ability of ddPCR to detect STEC in slices of beef already after sample incubation for 7 h at 37 °C while, in the case of sponges used for official controls, 9 h at 37 °C was needed. In this way, the ddPCR could represent an efficient method for detecting STEC and providing results in less time than the official method.

Aetiology of acute diarrhoea in children in Shanghai, 2015-2018

Diarrhoea remains a major cause of childhood morbidity and mortality worldwide. This study aimed to monitor the aetiology of acute diarrhoea in children in Shanghai. Paediatric outpatients with acute diarrhoea were enrolled in the study from Jan 2015 to Dec 2018. Faecal samples were collected for testing. Enteric bacteria were identified and typed by culture and serotyping, respectively. Enteric viruses were identified by real-time PCR. Enteric pathogens were identified in 1572 (58.4%) of the 2692 enrolled children with acute diarrhoea. Viruses were detected more frequently than bacteria (41.3% versus 25.0%). Nontyphoidal Salmonella spp. (NTS) was the most common (10.3%) bacteria isolated, followed by enteropathogenic Escherichia coli (EPEC) (6.5%), enteroaggregative Escherichia coli (EAEC) (6.2%), Campylobacter spp. (3.6%), enterotoxigenic Escherichia coli (ETEC) (1.1%), Shigella spp. (0.2%), and enterohemorrhagic Escherichia coli (EHEC) (0.1%). Rotavirus was the most common (16.0%) virus detected, followed by norovirus (15.5%), adenovirus (7.2%), sapovirus (3.0%) and astrovirus (2.7%). Rotavirus, norovirus and NTS were the major pathogens responsible for diarrhoea in Shanghainese children. Improving uptake of the rotavirus vaccine and strengthening foodborne-pathogen prevention will aid in reducing the burden of diarrhoeal disease in children in Shanghai.

Persistence of a Stx-Encoding Bacteriophage in Minced Meat Investigated by Application of an Improved DNA Extraction Method and Digital Droplet PCR

Shiga toxin-producing Escherichia coli (STEC) are important food-borne pathogens with Shiga toxins as the main virulence factor. Shiga toxins are encoded on Shiga toxin-encoding bacteriophages (Stx phages). Stx phages may exist as free bacteriophages in the environment or in foods or as prophages integrated into the host genome. From a food safety perspective, it is important to have knowledge on the survival and persistence of Stx phages in food products since these may integrate into the bacterial hosts through transduction if conditions are right. Here, we present the results from a study investigating the survival of a Stx phage in minced meat from beef stored at a suboptimal temperature (8°C) for food storage along with modifications and optimizations of the methods applied. Minced meat from beef was inoculated with known levels of a labeled Stx phage prior to storage. Phage filtrates were used for plaque assays and DNA extraction, followed by real-time PCR and digital droplet PCR (ddPCR). The results from the pilot study suggested that the initial DNA extraction protocol was not optimal, and several modifications were tested before a final protocol was defined. The final DNA extraction protocol comprised ultra-centrifugation of the entire phage filtrate for concentrating phages and two times phenol–chloroform extraction. The protocol was used for two spiking experiments. The DNA extraction protocol resulted in flexibility in the amount of DNA available for use in PCR analyses, ultimately increasing the sensitivity of the method used for quantification of phages in a sample. All three quantification methods employed (i.e., plaque assays, real-time PCR, and ddPCR) showed similar trends in the development of the phages during storage, where ddPCR has the benefit of giving absolute quantification of DNA copies in a simple experimental setup. The results indicate that the Stx phages persist and remain infective for at least 20 days under the storage conditions used in the present study. Stx phages in foods might represent a potential risk for humans. Although it can be speculated that transduction may take place at 8°C with subsequent forming of STEC, it can be expected to be a rare event. However, such an event may possibly take place under more optimal conditions, such as an increase in storage temperature of foods or in the gastrointestinal tract of humans.

Use of Genomics to Investigate Historical Importation of Shiga Toxin-Producing Escherichia coli Serogroup O26 and Nontoxigenic Variants into New Zealand

Shiga toxin-producing Escherichia coli serogroup O26 is an important public health pathogen. Phylogenetic bacterial lineages in a country can be associated with the level and timing of international imports of live cattle, the main reservoir. We sequenced the genomes of 152 E. coli O26 isolates from New Zealand and compared them with 252 E. coli O26 genomes from 14 other countries. Gene variation among isolates from humans, animals, and food was strongly associated with country of origin and stx toxin profile but not isolation source. Time of origin estimates indicate serogroup O26 sequence type 21 was introduced at least 3 times into New Zealand from the 1920s to the 1980s, whereas nonvirulent O26 sequence type 29 strains were introduced during the early 2000s. New Zealand's remarkably fewer introductions of Shiga toxin-producing Escherichia coli O26 compared with other countries (such as Japan) might be related to patterns of trade in live cattle.

Molecular characterisation of antibiotic-resistant Salmonella enterica isolates recovered from meat in South Africa

Salmonella enterica is a leading cause of human gastroenteritis in both developed and developing countries, causing significant economic losses on humans and animals worldwide. There are several routes for contracting salmonellosis, but the consumption of contaminated foods is by far the most frequent cause of human infections. This study aimed to assess the prevalence and resistance determinants of S. enterica isolates obtained from meat. Swab samples from meat were cultured for the identification of Salmonella spp., and 239 presumptive S. enterica isolates were recovered, purified and kept in glycerol stocks. The S. enterica. confirmed by polymerase chain reaction (PCR) were further tested against 15 antimicrobials using the disc-diffusion method on Muller-Hinton agar and the genotypic antimicrobial resistance determinants by PCR. Resistance among tetracyclines, bêta-lactams, and 3rd generation cephalosporins was found to be most frequent with a noticeable rise in the number of multi-drug resistance ranging from two to seven antimicrobials. A total of 20 resistance determinants were assessed with their prevalence and distributions obtained as follows; [aminoglycosides: aadA (89%), aacC2 (100%), aphA1 (38%), aphA2 (0%) and strA (7%)], [β-lactams: (ampC 100%), blaTEM, (33%), blaZ (17%) and blaOXA (10%)], [Chloramphenicol: catI (9%), catII (7%), and cmIA1 (10%)] and [tetracyclines: tetA (57%), tetB (30%), tetC (11%), tetD (73%), tetK (20%) and tetM, (43%)], and [sulfonamides: sulI (82%), sulII (7%)]. The findings signify a high prevalence of multidrug-resistant (MDR) S. enterica isolates and resistance determinants indicating increased public health risks associated with the consumption of contaminated meat.

Presence of Shiga Toxin-Producing Escherichia coli (STEC) in Fresh Beef Marketed in 13 Regions of ITALY (2017)

The aim of this study was to determine the prevalence of Shiga toxin-producing Escherichia coli in fresh beef marketed in 2017 in 13 regions of Italy, to evaluate the potential risk to human health. According to the ISO/TS 13136:2012 standard, 239 samples were analysed and nine were STEC positive, from which 20 strains were isolated. The STEC-positive samples were obtained from Calabria (n = 1), Campania (n = 1), Lazio (n = 2), Liguria (n = 1), Lombardia (n = 1) and Veneto (n = 3). All STEC strains were analysed for serogroups O26, O45, O55, O91, O103, O104, O111, O113, O121, O128, O145, O146 and O157, using Real-Time PCR. Three serogroups were identified amongst the 20 strains: O91 (n = 5), O113 (n = 2), and O157 (n = 1); the O-group for each of the 12 remaining STEC strains was not identified. Six stx subtypes were detected: stx1a, stx1c, stx2a, stx2b, stx2c and stx2d. Subtype stx2c was the most common, followed by stx2d and stx2b. Subtype stx2a was identified in only one eae-negative strain and occurred in combination with stx1a, stx1c and stx2b. The presence in meat of STEC strains being potentially harmful to human health shows the importance, during harvest, of implementing additional measures to reduce contamination risk.

An investigation of shedding and super-shedding of Shiga toxigenic Escherichia coli O157 and E. coli O26 in cattle presented for slaughter in the Republic of Ireland

Shiga toxigenic Escherichia coli (STEC) are an important group of pathogens and can be transmitted to humans from direct or indirect contact with cattle faeces. This study investigated the shedding of E. coli O157 and O26 in cattle at the time of slaughter and factors associated with super-shedding (SS) animals. Rectoanal mucosal swab (RAMS) samples were collected from cattle (n = 1,317) at three large Irish commercial beef abattoirs over an 18 month period, and metadata were collected at the time of sampling regarding farm of origin, animal age, breed and gender. RAMS swabs were examined for the presence and numbers of E. coli O157 and O26 using a previously developed quantitative real-time PCR protocol. Samples positive by PCR were culturally examined and isolates analysed for the presence of stx subtypes, eae and phylogroup. Any samples with counts >10⁴  CFU/swab of STEC O157 or O26 were deemed to be super-shedders. Overall, 4.18% (55/1,317) of RAMS samples were positive for STEC O157, and 2.13% (28/1,317) were classified as STEC O157 SS. For STEC O26, 0.76% (10/1,317) of cattle were positive for STEC O26, and 0.23% (3/1,317) were classified as super-shedders. Fewer STEC shedders and SS were noted among older animals (>37 months). There was a seasonal trend observed for STEC O157, with the highest prevalence of shedding and SS events in the autumn (August to October). The majority of E. coli O157 (50/55) isolates had stx2 and were eae positive, with no significant difference between SS and low shedders (LS). Interestingly, all STEC O26 (n = 10) were eae negative and had varied stx profiles. This study demonstrates that, while the overall shedding rates are relatively low in cattle at slaughter, among positive animals there is a high level of SS, which may pose a higher risk of cross-contamination during slaughter.

Molecular Epidemiology of Shiga Toxin-Producing Escherichia coli (STEC) on New Zealand Dairy Farms: Application of a Culture-Independent Assay and Whole-Genome Sequencing

New Zealand has a relatively high incidence of human cases of Shiga toxin-producing Escherichia coli (STEC), with 8.9 STEC cases per 100,000 people reported in 2016. Previous research showed living near cattle and contact with cattle feces as significant risk factors for STEC infections in humans in New Zealand, but infection was not linked to food-associated factors. During the 2014 spring calving season, a random, stratified, cross-sectional study of dairy farms (n = 102) in six regions across New Zealand assessed the prevalence of the "Top 7" STEC bacteria (serogroups O157, O26, O45, O103, O111, O121, and O145) in young calves (n = 1,508), using a culture-independent diagnostic test (PCR/MALDI-TOF). Twenty percent (306/1,508) of calves on 75% (76/102) of dairy farms were positive for at least one of the "Top 7" STEC bacteria. STEC carriage by calves was associated with environmental factors, increased calf age, region, and increased number of calves in a shared calf pen. The intraclass correlation coefficient (ρ) indicated strong clustering of "Top 7" STEC-positive calves for O157, O26, and O45 serogroups within the same pens and farms, indicating that if one calf was positive, others in the same environment were likely to be positive as well. This finding was further evaluated with whole-genome sequencing, which indicated that a single E. coli O26 clonal strain could be found in calves in the same pen or farm, but different strains existed on different farms. This study provides evidence that would be useful for designing on-farm interventions to reduce direct and indirect human exposure to STEC bacteria.IMPORTANCE Cattle are asymptomatic carriers of Shiga toxin-producing E. coli (STEC) bacteria that can cause bloody diarrhea and kidney failure in humans if ingested. New Zealand has relatively high numbers of STEC cases, and contact with cattle feces and living near cattle are risk factors for human infection. This study assessed the national prevalence of STEC in young dairy cattle by randomly selecting 102 farms throughout New Zealand. The study used a molecular laboratory method that has relatively high sensitivity and specificity compared to traditional methods. "Top 7" STEC was found in 20% of calves on 75% of the farms studied, indicating widespread prevalence across the country. By examining the risk factors associated with calf carriage, potential interventions that could decrease the prevalence of "Top 7" STEC bacteria at the farm level were identified, which could benefit both public health and food safety.

A network of regulators promotes dehydration tolerance in Escherichia coli

The ability to survive conditions of low water activity is critical for the survival of many bacteria in the environment and facilitates disease transmission through food and contaminated surfaces. However, the molecular mechanisms that enable bacteria to withstand this condition remain poorly understood. Here we describe a network of regulators in Escherichia coli that are important for this bacterium to survive dehydration. We found that the transcriptional regulator DksA and the general stress response regulator RpoS play a critical role. From a plasmid genomic library screen, we identified two additional regulators, Crl and ArcZ, that promote dehydration tolerance through modulation of RpoS. We also found that LexA, RecA and ArcA contribute to survival. Our results identify key regulators that enable E. coli to tolerate dehydration and suggest a hierarchical network is involved in protection against cellular damage associated with this stress.

Multiplexed Single Intact Cell Droplet Digital PCR (MuSIC ddPCR) Method for Specific Detection of Enterohemorrhagic E. coli (EHEC) in Food Enrichment Cultures

Foodborne illness attributed to enterohemorrhagic E. coli (EHEC), a highly pathogenic subset of Shiga toxin-producing E. coli (STEC), is increasingly recognized as a significant public health issue. Current microbiological methods for identification of EHEC in foods often use PCR-based approaches to screen enrichment broth cultures for characteristic gene markers [i.e., Shiga toxin (stx) and intimin (eae)]. However, false positives arise when complex food matrices, such as beef, contain mixtures of eae-negative STEC and eae-positive E. coli, but no EHEC with both markers in a single cell. To reduce false-positive detection of EHEC in food enrichment samples, a Multiplexed, Single Intact Cell droplet digital PCR (MuSIC ddPCR) assay capable of detecting the co-occurrence of the stx and eae genes in a single bacterial cell was developed. This method requires: (1) dispersal of intact bacteria into droplets; (2) release of genomic DNA (gDNA) by heat lysis; and (3) amplification and detection of genetic targets (stx and eae) using standard TaqMan chemistries with ddPCR. Performance of the method was tested with panels of EHEC and non-target E. coli. By determining the linkage (i.e., the proportion of droplets in which stx and eae targets were both amplified), samples containing EHEC (typically greater than 20% linkage) could be distinguished from samples containing mixtures of eae-negative STEC and eae-positive E. coli (0–2% linkage). The use of intact cells was necessary as this linkage was not observed with gDNA extracts. EHEC could be accurately identified in enrichment broth cultures containing excess amounts of background E. coli and in enrichment cultures derived from ground beef/pork and leafy-green produce samples. To our knowledge, this is the first report of dual-target detection in single bacterial cells using ddPCR. The application of MuSIC ddPCR to enrichment-culture screening would reduce false-positives, thereby improving the cost, speed, and accuracy of current methods for EHEC detection in foods.

A study on association of virulence determinants of verotoxic Escherichia coli isolated from cattle calves

AIM

The present study was conducted to find the association among virulence determinants of verotoxic Escherichia coli (VTEC) isolated from cattle calf feces.

MATERIALS AND METHODS

A total of 216 cattle calf fecal samples were collected aseptically and processed under required conditions for the isolation of E. coli. The isolates were further subjected to multiplex polymerase chain reaction (mPCR) for the detection of virulent genes. All the VTEC isolates were serotyped at the Central Research Institute, Kasauli, Himachal Pradesh. The VTEC isolates were observed for the enterohemolysin production on washed sheep blood agar (wSBA).

RESULTS

A total of 177 presumptive E. coli were isolated from 216 calf fecal samples revealing an overall prevalence of E. coli to be 81.94%. A total of 32 (14.81%) isolates were detected as VTEC through mPCR. The prevalence of verotoxin genes vt1, vt2, and combination of vt1+vt2 in the VTEC isolates was found to be 12 (37.5%), 14 (43.75%), and 6 (18.75%), respectively. Other virulent genes eaeA and hlyA were found in 6 and 11 VTEC strains with prevalence values of 18.75% and 34.37%, respectively. A total of 13 different O serogroups were revealed in serotyping of 32 VTEC isolates. Out of 32 VTEC strains, only 26 (81.25%) were enterohemolytic on wSBA as they produced the characteristic small, turbid zone of hemolysis around the streaking line. Although enterohemolysin production has been attributed to the presence of hlyA gene, only 11 of 26 enterohemolysin producing VTEC were found to be harboring the hlyA gene (11/26) 42.03%.

CONCLUSION

The present study concludes that there might be an association between the presence of verotoxin genes and enterohemolysin production in VTEC group of E. coli.

Comparison of Agar Media for Detection and Quantification of Shiga Toxin-Producing Escherichia coli in Cattle Feces

The isolation and quantification of non-O157 Shiga toxin-producing Escherichia coli (STEC) from cattle feces are challenging. The primary objective of this study was to evaluate the performance of selected agar media in an attempt to identify an optimal medium for the detection and quantification of non-O157 STEC in cattle feces. Comparison studies were performed using CHROMagar STEC, Possé differential agar (Possé), Possé modified by the reduction or addition of antimicrobials, STEC heart infusion washed blood agar with mitomycin C (SHIBAM), and SHIBAM modified by the addition of antimicrobials. Fourteen STEC strains, two each belonging to serogroups O26, O45, O103, O111, O121, O145, and O157, were used to test detection in inoculated fecal suspensions at concentrations of 10(2) or 10(3) CFU/g. One STEC strain from each of these seven serogroups was used to estimate the concentration of recovered STEC in feces inoculated at 10(3), 10(4), or 10(5) CFU/g. Significantly more suspensions (P < 0.05) were positive for STEC when plated on Possé containing reduced concentrations of novobiocin and potassium tellurite compared with SHIBAM, but not SHIBAM modified by containing these same antimicrobials at the same concentrations. Numerically, more suspensions were positive for STEC by using this same form of modified Possé compared with Possé, but this difference was not statistically significant. More suspensions were positive for STEC cultured on CHROMagar STEC compared with those on Possé (P < 0.05) and on modified Possé (P = 0.05). Most inoculated fecal suspensions below 10(4) CFU/g of feces were underestimated or not quantifiable for the concentration of STEC by using CHROMagar STEC or modified Possé. These results suggest that CHROMagar STEC performs better than Possé or SHIBAM for detection of STEC in bovine feces, but adjustments in the concentrations of novobiocin and potassium tellurite in the latter two media result in significant improvements in their performance.

Comparison of Droplet Digital PCR and qPCR for the Quantification of Shiga Toxin-Producing Escherichia coli in Bovine Feces

Cattle are considered to be the main reservoir for Shiga toxin-producing Escherichia coli (STEC) and are often the direct or indirect source of STEC outbreaks in humans. Accurate measurement of the concentration of shed STEC in cattle feces could be a key answer to questions concerning transmission of STEC, contamination sources and efficiency of treatments at farm level. Infected animals can be identified and the contamination level quantified by real-time quantitative PCR (qPCR), which has its specific limitations. Droplet digital PCR (ddPCR) has been proposed as a method to overcome many of the drawbacks of qPCR. This end-point amplification PCR is capable of absolute quantification independent from any reference material and is less prone to PCR inhibition than qPCR. In this study, the qPCR-based protocol described by Verstraete et al. (2014) for Shiga toxin genes stx1 and stx2 and the intimin gene eae quantification was optimized for ddPCR analysis. The properties of ddPCR and qPCR using two different mastermixes (EMM: TaqMan(®) Environmental Master Mix 2.0; UMM: TaqMan(®) Universal PCR Master Mix) were evaluated, using standard curves and both artificial and natural contaminated cattle fecal samples. In addition, the susceptibility of these assays to PCR-inhibitors was investigated. Evaluation of the standard curves and both artificial and natural contaminated cattle fecal samples suggested a very good agreement between qPCR using EMM and ddPCR. Furthermore, similar sensitivities and no PCR inhibition were recorded for both assays. On the other hand, qPCR using UMM was clearly prone to PCR inhibition. In conclusion, the ddPCR technique shows potential for the accurate absolute quantification of STEC on the farms, without relying on standardized reference material.

The response of foodborne pathogens to osmotic and desiccation stresses in the food chain

In combination with other strategies, hyperosmolarity and desiccation are frequently used by the food processing industry as a means to prevent bacterial proliferation, and particularly that of foodborne pathogens, in food products. However, it is increasingly observed that bacteria, including human pathogens, encode mechanisms to survive and withstand these stresses. This review provides an overview of the mechanisms employed by Salmonella spp., Shiga toxin producing E. coli, Cronobacter spp., Listeria monocytogenes and Campylobacter spp. to tolerate osmotic and desiccation stresses and identifies gaps in knowledge which need to be addressed to ensure the safety of low water activity and desiccated food products.

The significance of clean and dirty animals for bacterial dynamics along the beef chain

This study investigated the bacterial dynamics along the beef chain for clean and dirty cattle in the slaughter and processing lines, using classic quantitative methods and molecular analyses. In addition, the Norwegian national guidelines for Good Hygiene Practices in Norway were evaluated. In these guidelines, cattle presented for slaughter are categorised according to hide cleanliness, resulting in separate processing lines for meat from very dirty animals and reduced prices to farmers. The study was conducted in two commercial abattoirs in Norway. Two groups were compared; 40 visually clean cattle and 40 visually dirty cattle presented for slaughter, with 20 from each group at each abattoir. The same animals were sampled at five sampling sites: hides, carcass surfaces after dehiding, just before chilling, after chilling, and meat trimmings. Meat trimmings were sampled in only one abattoir. Three hundred and sixty samples were collected by swabbing 100 cm(2) of the brisket area at the first four sampling sites, and sampling 200 g of meat trimmings at the fifth site. The results showed that the hides of dirty cattle had more Enterobacteriaceae and higher Aerobic Plate Counts (APC) than visually clean cattle (P<0.05), however there was no significant difference for Escherichia coli. For the other sampling sites, there were no differences between the dirty and the clean group. An effect of chilling/drying of the carcass surfaces was demonstrated by the significant reduction in the number of carcasses on which E. coli and Enterobacteriaceae were detected; from 11% and 39% before chilling to 1% and 16% after chilling, respectively. Enterobacteriaceae and E. coli were detected in only three and one of the meat trimming samples, respectively. Amplification and sequencing of the 16S rRNA gene from 643 Enterobacteriaceae colonies derived from 107 samples demonstrated that Escherichia/Shigella were dominant within this family on the hides. However, after dehiding, after grading, and after chilling, the genera Citrobacter and Enterobacter dominated. The meat trimmings were dominated by the genera Kluyvera, Hafnia, and unclassified Enterobacteriaceae. The relative proportions of Escherichia/Shigella were higher for dirty animals than for clean animals, and were higher on hides than from sampling sites further down the chain (P<0.05). The minor differences in contamination on carcass surfaces and meat trimmings between clean and dirty cattle indicate that separate processing lines in Norwegian abattoirs seem to be unnecessary.

Genetic Diversity of the fliC Genes Encoding the Flagellar Antigen H19 of Escherichia coli and Application to the Specific Identification of Enterohemorrhagic E. coli O121:H19

Enterohemorrhagic Escherichia coli (EHEC) O121:H19 belong to a specific clonal type distinct from other classical EHEC and major enteropathogenic E. coli groups and is regarded as one of the major EHEC serogroups involved in severe infections in humans. Sequencing of the fliC genes associated with the flagellar antigen H19 (fliCH19) revealed the genetic diversity of the fliCH19 gene sequences in E. coli. A cluster analysis of 12 fliCH19 sequences, 4 from O121 and 8 from non-O121 E. coli strains, revealed five different genotypes. All O121:H19 strains fell into one cluster, whereas a second cluster was formed by five non-O121:H19 strains. Cluster 1 and cluster 2 strains differ by 27 single nucleotide exchanges in their fliCH19 genes (98.5% homology). Based on allele discrimination of the fliCH19 genes, a real-time PCR test was designed for specific identification of EHEC O121:H19. The O121 fliCH19 PCR tested negative in 73 E. coli H19 strains that belonged to serogroups other than O121, including 28 different O groups, O-nontypeable H19, and O-rough:H19 strains. The O121 fliCH19 PCR reacted with all 16 tested O121:H19 strains and 1 O-rough:H19 strain which was positive for the O121 wzx gene. A cross-reaction was observed only with E. coli H32 strains which share sequence similarities in the target region of the O121 fliCH19 PCR. The combined use of O-antigen genotyping (O121 wzx) and the detection of O121 fliCH19 allele type contributes to improving the identification and molecular serotyping of EHEC O121:H19 motile and nonmotile strains and variants of these strains lacking stx genes.

Shiga toxin-producing Escherichia coli O157, O26 and O111 in cattle faeces and hides in Italy

INTRODUCTION

Ruminants are regarded as the natural reservoir for Shiga toxin-producing Escherichia coli (STEC), especially of serogroup O157.

MATERIALS AND METHODS

During 2011 and 2012, 320 samples (160 faecal samples from the rectum and 160 hide samples from the brisket area) were collected from 160 cattle at slaughter in Northern Italy during warm months (May to October). Cattle were reared in different farms and their age at slaughter ranged between nine months and 15 years, most of them being culled cattle (median age: six years; average age: 4.6 years). Samples were tested by immunomagnetic-separation technique for E coli O157 and O26 and by a screening PCR for stx genes followed by cultural detection of STEC. The virulence genes stx1, stx2, eae, and e-hlyA were detected and among stx2-positive isolates the presence of the stx2a and stx2c variants was investigated.

RESULTS

Twenty-one of 160 cattle (13.1 per cent; 95 per cent CI 8.3 to 19.4 per cent) were found to be faecal carriers of STEC. STEC O157 was found in 10 (6.3 per cent) samples, STEC O26 in six (3.8 per cent) and STEC O111 in one (0.6 per cent). Four isolates (2.5 per cent) were O not determined (OND). Six out of 160 (3.8 per cent; 95 per cent CI 1.4 to 8.0 per cent) hide samples were positive for STEC; four hides (2.5 per cent) were contaminated by STEC O157 and two (1.3 per cent) by STEC O26. In three cattle (1.9 per cent) STEC from both faeces and hides were detected. Among STEC O157, 87.5 per cent of them carried the stx2c gene and 12.5 per cent carried both stx1 and stx2c genes. No O157 isolate harboured stx2a variant. STEC O26 and O111 carried the stx1 gene only. One OND strain carried both the stx2a and stx2c genes.

CONCLUSIONS

This study shows that STEC O157 from cattle can harbour the stx2c variant, which is associated with haemolytic uraemic syndrome in humans, and that cattle hides may be a source of human pathogenic STEC O157 and O26 in the slaughterhouse environment.