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

Characterization of diarrheagenic Escherichia coli from different cattle production systems in Brazil

Diarrheagenic E. coli (DEC) can cause severe diarrhea and is a public health concern worldwide. Cattle are an important reservoir for this group of pathogens, and once introduced into the abattoir environment, these microorganisms can contaminate consumer products. This study aimed to characterize the distribution of DEC [Shiga toxin-producing E. coli (STEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), and enteroaggregative E. coli (EAEC)] from extensive and intensive cattle production systems in Brazil. Samples (n = 919) were collected from animal feces (n = 200), carcasses (n = 600), meat cuts (n = 90), employee feces (n = 9), and slaughterhouse water (n = 20). Virulence genes were detected by PCR in 10% of animal samples (94/919), with STEC (n = 81) as the higher prevalence, followed by EIEC (n = 8), and lastly EPEC (n = 5). Animals raised in an extensive system had a higher prevalence of STEC (average 48%, sd = 2.04) when compared to animals raised in an intensive system (23%, sd = 1.95) (Chi-square test, P < 0.001). From these animals, most STEC isolates only harbored stx2 (58%), and 7% were STEC LEE-positive isolates that were further identified as O157:H7. This study provides further evidence that cattle are potential sources of DEC, especially STEC, and that potentially pathogenic E. coli isolates are widely distributed in feces and carcasses during the slaughter process.

Study of the transfer of Shiga toxin-producing Escherichia coli during the slaughter of cattle using molecular typing combined with epidemiologic data

Investigation on the distribution and biological characteristics of Shiga-toxin producing Escherichia coli (STEC) during beef processing is essential for in-plant critical control points and food safety risk assessment. Serogroups and subtypes of stx genes of STEC strains isolated from beef processing lines were first investigated. Identification to cross-contamination among different sampling sites was further conducted by combining multilocus sequence typing (MLST) with the previous distribution and characterization data. The PCR-positive rate for STEC in 435 samples from two slaughter plants in China was 14.3% and the isolation rate for the 62 PCR positive and the entire set of 435 samples were 26% and 3.68% respectively. The existence of serotype O157:H7 (33%) and serogroups O121 (42%) and O26 (21%) as well as the high detection rate of high pathogenic gene stx2a (68%) in these serogroups indicated potential risk to the safety of beef. Traceability analysis showed that hide plays a critical role in cross-contamination between feces, lairage pens and post-washing carcasses from a molecular perspective. Intervening measures revolves around de-hiding should be involved in the in-plant safety control policy according to the tracing analysis.

Broad time-dependent transcriptional activity of metabolic genes of E. coli O104:H4 strain C227/11Φcu in a soil microenvironment at low temperature

In the current study, metabolic genes and networks that influence the persistence of pathogenic Escherichia coli O104:H4 strain C227/11Φcu in agricultural soil microenvironments at low temperature were investigated. The strain was incubated in alluvial loam (AL) and total RNA was prepared from samples at time point 0, and after 1 and 4 weeks. Differential transcriptomic analysis was performed by RNA sequencing analysis and values obtained at weeks 1 and 4 were compared to those of time point 0. We found differential expression of more than 1500 genes for either time point comparison. The two lists of differentially expressed genes were then subjected to gene set enrichment of Gene Ontology terms. In total, 17 GO gene sets and 3 Pfam domains were found to be enriched after 1 week. After 4 weeks, 17 GO gene sets and 7 Pfam domains were statistically enriched. Especially stress response genes and genes of the primary metabolism were particularly affected at both time points. Genes and gene sets for uptake of carbohydrates, amino acids were strongly upregulated, indicating adjustment to a low nutrient environment. The results of this transcriptome analysis show that persistence of C227/11Φcu in soils is associated with a complex interplay of metabolic networks.

Sporadic Detection of Escherichia coli O104:H4 Strain C227/11Φcu in the Edible Parts of Lamb's Lettuce Cultured in Contaminated Agricultural Soil Samples

In the current study, we demonstrate that E. coli O104:H4 strain C227/11Φcu, a derivative of the 2011 enterohemorrhagic/enteroaggregative (EHEC/EAEC) E. coli outbreak strain, migrated into the edible portion of lamb's lettuce plants upon contamination of the surrounding soil. Seeds were surface-sterilized and cultivated on Murashige-Skoog agar or in autoclaved agricultural soil. Migration into the edible portions was investigated by inoculating the agar or soil close to the plants with 108 colony-forming units (CFU). The edible parts, which did not come into contact with the contaminated medium or soil, were quantitatively analyzed for the presence of bacteria after 2, 4 and 8 weeks. Strain C227/11Φcu could colonize lamb's lettuce when contamination of medium or soil occurs. The highest recovery rate (27%) was found for lettuce cultivated in agar, and up to 1.6 × 103 CFU/g lettuce was detected. The recovery rate was lower for the soil samples (9% and 13.5%). Although the used contamination levels were high, migration of C227/11Φcu from the soil into the edible parts was demonstrated. This study further highlights the risk of crop plant contamination with pathogenic E. coli upon soil contamination.

Phylogenetic group and virulence profile classification in Escherichia coli from distinct isolation sources in Mexico

Escherichia coli is a leading cause of human enteric diseases worldwide. The rapid and accurate causal agent identification to a particular source represents a crucial step in the establishment of safety and health measures in the affected human populations and would thus provide insights into the relationship of traits that may contribute for pathogen persistence in a particular reservoir. The objective of the present study was to characterize over two hundred E. coli strains from different isolation sources in Mexico by conducting a correspondence analysis to explore associations with the detected phylogenetic groups. The results indicated that E. coli strains, recovered from distinct sources in Mexico, were classified into phylogroups B1 (35.8%), A (27.8%), and D (12.3%) and were clustered to particular clades according to the predicted phylogroups. The results from correspondence analysis showed that E. coli populations from distinct sources in Mexico, belonging to different phylogroups, were not dispersed randomly and were associated with a particular isolation source. Phylogroup A was strongly associated with human sources, and the phylogroup B1 showed a significant relationship with food sources. Additionally, phylogroup D was also related to human sources. Phylogroup B2 was associated with herbivorous and omnivorous mammals. Moreover, common virulence genes in the examined E. coli strains, assigned to all phylogroups, were identified as essential markers for survival and invasion in the host. Although virulence profiles varied among the detected phylogroups, E. coli strains belonging to phylogroup D, associated with humans, were found to contain the largest virulence gene repertoire conferring for persistence and survival in the host. In summary, these findings provide fundamental information for a better characterization of pathogenic E. coli, recovered from distinct isolation sources in Mexico and would assist in the development of better tools for identifying potential transmission routes of contamination.

The "Big Six": Hidden Emerging Foodborne Bacterial Pathogens

Non-O157 Shiga toxin-producing Escherichia coli (STEC) are emerging serogroups that often result in diseases ranging from diarrhea to severe hemorrhagic colitis in humans. The most common non-O157 STEC are O26, O45, O103, O111, O121, and O145. These serogroups are known by the name "big six" because they cause severe illness and death in humans and the United States Department of Agriculture declared these serogroups as food contaminants. The lack of fast and efficient diagnostic methods exacerbates the public impact of the disease caused by these serogroups. Numerous outbreaks have been reported globally and most of these outbreaks were caused by ingestion of contaminated food or water as well as direct contact with reservoirs. Livestock harbor a variety of non-O157 STEC serovars that can contaminate meat and dairy products, or water sources when used for irrigation. Hence, effective control and prevention approaches are required to safeguard the public from infections. This review addresses the disease characteristics, reservoirs, the source of infections, the transmission of the disease, and major outbreaks associated with the six serogroups ("big six") of non-O157 STEC encountered all over the globe.

Super Shedding in Enteric Pathogens: A Review

Super shedding occurs when a small number of individuals from a given host population shed high levels of a pathogen. Beyond this general definition, various interpretations of the shedding patterns have been proposed to identify super shedders, leading to the description of the super shedding phenomenon in a wide range of pathogens, in particular enteric pathogens, which are of considerable interest. Several underlying mechanisms may explain this observation, including factors related to the environment, the gut microbiota, the pathogen itself (i.e., genetic polymorphism), and the host (including immune factors). Moreover, data suggest that the interplay of these parameters, in particular at the host-pathogen-gut microbiota interface, is of crucial importance for the determination of the super shedding phenotype in enteric pathogens. As a phenomenon playing an important role in the epidemics of enteric diseases, the evidence of super shedding has highlighted the need to develop various control strategies.

Investigation of Escherichia coli O157 and Listeria monocytogenes presence and antibiotic susceptibility isolated from ruminant feces and feeds in Balikesir province

In this study, which was conducted for the first time in Balıkesir, it was purposed to determine the existense, virulence factors and antibiotic susceptibility of Escherichia coli O157, which is zoonotic in ruminant feces and feed, and the pathogen Listeria monocytogenes, which causes diseases in humans and animals, and to use these results as epidemiological data in our province, region and country. Feces and animal feed samples were analyzed simultaneously for in order of E. coli O157 and L. Monocytogenes according to ISO 16654: 2001 / Amd 1: 2017 and ISO 11290-1. 38 E.coli O157 was isolated from a total of one hunderd stool samples. 18 L. monocytogenes were isolated from a total of one hunderd stool samples. 6 L. monocytogenes were isolated from 50 silage samples. Three of these isolates were isolated from faeces and silage samples taken from the same farm with L. monocytogenes isolates isolated from sheep feces. E. coli O157 could not be isolated from a total of 100 silage and feed samples. All L. monocytogenes isolates were susceptible to sulfamethoxazole / trimethoprim, tetracycline, streptomycin, meropenem and erythromycin. The highest resistance was detected against Sulbactam / ampicillin. 3 E. coli O157 isolates were found resistant to Gentamicin and 7 isolates to Tobramycin. 21 isolates were resistant to erythromycin, and 12 isolates were intermediate. According to PCR results of fliCH7, Stx1, Stx2, eaeA and EhlyA genes, EhlyA gene was found in 20 E. coli O157 isolates. Of these isolates, 4 were isolated from sheep feces and 16 from calf feces. The stx1 gene was found in a total of 5 E. coli O157 isolates, one from sheep feces and four from calf feces. EhlyA gene was also found in all isolates with stx1 gene. The stx2 gene was found in a total of 3 E. coli O157 isolates, one from sheep dung and two from calf dung. Intimin gene was found in 8 E. coli O157 isolates, two of which are sheep faeces and six calf faecal isolates. EhlyA gene was found in all isolates with intimin gene. In this study, enterohaemolysin is the predominant virulence factor among the isolates. Epidemiologically, silage was thought to be the main source of L. monocytogenes contamination, and recently, silage contamination continued in Balikesir.

Management-intensive grazing impacts on total Escherichia coli, E. coli O157:H7, and antibiotic resistance genes in a riparian stream

The impacts of management-intensive grazing (MIG) of cattle on concentrations of total Escherichia coli, total suspended solids (TSS), and nitrate-nitrite nitrogen (NO₃ + NO₂-N), and occurrence of E. coli O157:H7 and selected antibiotic resistance genes (ARGs) in stream water and/or sediments were evaluated. Cattle were grazed for two-week periods in May in each of three years. Overall, grazing increased total E. coli in downstream water by 0.89 log₁₀ MPN/100 mL (p < 0.0001), and downstream total E. coli concentrations were higher than upstream over all sampling intervals. Downstream TSS levels also increased (p ≤ 0.0294) during grazing. In contrast, there was a main effect of treatment for downstream NO₃ + NO₂-N to be lower than upstream (3.59 versus 3.70 mg/L; p = 0.0323). Overwintering mallard ducks increased total E. coli and TSS concentrations in January and February (p < 0.05). For precipitation events during the 24 h before sampling, each increase of 1.00 cm of rainfall increased total E. coli by 0.49 log₁₀ MPN/100 mL (p = 0.0005). In contrast, there was no association of previous 24 h precipitation volume on TSS (p = 0.1540), and there was a negative linear effect on NO₃ + NO₂-N (p = 0.0002). E. coli O157:H7 prevalence was low, but the pathogen was detected downstream up to 2½ months after grazing. Examination of ARGs sul1, ermB, bla_ctx-m-32, and intI1 identified the need for additional research to understand the impact of grazing on the ecology of these resistance determinants in pasture-based cattle production. While E. coli remained higher in downstream water compared to upstream, MIG may reduce the magnitude of the downstream E. coli concentrations. Likewise, the MIG strategy may prevent large increases in TSS and NO₃ + NO₂-N concentrations during heavy rain events. Results indicate that MIG can limit the negative effects of cattle grazing on stream water quality.

Prevalence and Whole-Genome Sequence-Based Analysis of Shiga Toxin-Producing Escherichia coli Isolates from the Recto-Anal Junction of Slaughter-Age Irish Sheep

Shiga toxin-producing Escherichia coli (STEC) organisms are a diverse group of pathogenic bacteria capable of causing serious human illness, and serogroups O157 and O26 are frequently implicated in human disease. Ruminant hosts are the primary STEC reservoir, and small ruminants are important contributors to STEC transmission. This study investigated the prevalence, serotypes, and shedding dynamics of STEC, including the supershedding of serogroups O157 and O26, in Irish sheep. Recto-anal mucosal swab samples (n = 840) were collected over 24 months from two ovine slaughtering facilities. Samples were plated on selective agars and were quantitatively and qualitatively assessed via real-time PCR (RT-PCR) for Shiga toxin prevalence and serogroup. A subset of STEC isolates (n = 199) were selected for whole-genome sequencing and analyzed in silico. In total, 704/840 (83.8%) swab samples were Shiga toxin positive following RT-PCR screening, and 363/704 (51.6%) animals were subsequently culture positive for STEC. Five animals were shedding STEC O157, and three of these were identified as supershedders. No STEC O26 was isolated. Post hoc statistical analysis showed that younger animals are more likely to harbor STEC and that STEC carriage is most prevalent during the summer months. Following sequencing, 178/199 genomes were confirmed as STEC. Thirty-five different serotypes were identified, 15 of which were not yet reported for sheep. Serotype O91:H14 was the most frequently reported. Eight Shiga toxin gene variants were reported, two stx₁ and six stx₂, and three novel Shiga-toxin subunit combinations were observed. Variant stx_1c was the most prevalent, while many strains also harbored stx_2b. IMPORTANCE Shiga toxin-producing Escherichia coli (STEC) bacteria are foodborne, zoonotic pathogens of significant public health concern. All STEC organisms harbor stx, a critical virulence determinant, but it is not expressed in most serotypes. Sheep shed the pathogen via fecal excretion and are increasingly recognized as important contributors to the dissemination of STEC. In this study, we have found that there is high prevalence of STEC circulating within sheep and that prevalence is related to animal age and seasonality. Further, sheep harbor a variety of non-O157 STEC, whose prevalence and contribution to human disease have been underinvestigated for many years. A variety of Stx variants were also observed, some of which are of high clinical importance.

Survival of Enterohemorrhagic Escherichia coli O104:H4 Strain C227/11Φcu in Agricultural Soils Depends on rpoS and Environmental Factors

The consumption of contaminated fresh produce caused outbreaks of enterohemorrhagic (EHEC) Escherichia coli. Agricultural soil might be a reservoir for EHEC strains and represent a contamination source for edible plants. Furthermore, the application of manure as fertilizer is an important contamination route. Thus, the German fertilizer ordinance prohibits the use of manure 12 weeks before crop harvest to avoid pathogen transmission into the food chain. In this study, the survival of E. coli O104:H4 strain C227/11Φcu in soil microenvironments with either diluvial sand or alluvial loam at two temperatures was investigated for more than 12 weeks. It was analyzed whether the addition of cattle manure extends EHEC survival in these microenvironments. The experiments were additionally performed with isogenic ΔrpoS and ΔfliC deletion mutants of C227/11Φcu. The survival of C227/11Φcu was highest at 4 °C, whereas the soil type had a minor influence. The addition of cattle manure increased the survival at 22 °C. Deletion of rpoS significantly decreased the survival period under all cultivation conditions, whereas fliC deletion did not have any influence. The results of our study demonstrate that EHEC C227/11Φcu is able to survive for more than 12 weeks in soil microenvironments and that RpoS is an important determinant for survival.

Epidemiological investigations identified an outbreak of Shiga toxin-producing Escherichia coli serotype O26:H11 associated with pre-packed sandwiches

In October 2019, public health surveillance systems in Scotland identified an increase in the number of reported infections of Shiga toxin-producing Escherichia coli (STEC) O26:H11 involving bloody diarrhoea. Ultimately, across the United Kingdom (UK) 32 cases of STEC O26:H11 stx1a were identified, with the median age of 27 years and 64% were male; six cases were hospitalised. Among food exposures there was an association with consuming pre-packed sandwiches purchased at outlets belonging to a national food chain franchise (food outlet A) [odds ratio (OR) = 183.89, P < 0.001]. The common ingredient identified as a component of the majority of the sandwiches sold at food outlet A was a mixed salad of Apollo and Iceberg lettuce and spinach leaves. Microbiological testing of food and environmental samples were negative for STEC O26:H11, although STEC O36:H19 was isolated from a mixed salad sample taken from premises owned by food outlet A. Contamination of fresh produce is often due to a transient event and detection of the aetiological agent in food that has a short-shelf life is challenging. Robust, statistically significant epidemiological analysis should be sufficient evidence to direct timely and targeted on-farm investigations. A shift in focus from testing the microbiological quality of the produce to investigating the processes and practices through the supply chain and sampling the farm environment is recommended.

Molecular detection of Shiga toxin-producing Escherichia coli (STEC) O157 in sheep, goats, cows and buffaloes

BACKGROUND

Shiga toxin-producing E. coli (STEC) are important foodborne pathogens that causing serious public health consequences worldwide. The present study aimed to estimate the prevalence ratio and to identify the zoonotic potential of E. coli O157 isolates in slaughtered adult sheep, goats, cows and buffaloes.

MATERIALS AND METHODS

A total of 400 Recto-anal samples were collected from two targeted sites Rawalpindi and Islamabad. Among them, 200 samples were collected from the slaughterhouse of Rawalpindi included sheep (n = 75) and goats (n = 125). While, 200 samples were collected from the slaughterhouse of Islamabad included cows (n = 120) and buffalos (n = 80). All samples were initially processed in buffered peptone water and then amplified by conventional PCR. Samples positive for E. coli O157 were then streaked onto SMAC media plates. From each positive sample, six different Sorbitol fermented pink-colored colonies were isolated and analyzed again via conventional PCR to confirm the presence of rfbE O157 gene. Isolates positive for rfbE O157 gene were then further analyzed by multiplex PCR for the presence of STEC other virulent genes (sxt1, stx2, eae and ehlyA) simultaneously.

RESULTS

Of 400 RAJ samples only 2 (0.5%) showed positive results for E. coli O157 gene, included sheep 1/75 (1.33%) and buffalo 1/80 (1.25%). However, goats (n = 125) and cows (n = 120) found negative for E. coli O157. Only 2 isolates from each positive sample of sheep (1/6) and buffalo (1/6) harbored rfbE O157 genes, while five isolates could not. The rfbE O157 isolate (01) of sheep sample did not carry any of STEC genes, while the rfbE O157 isolate (01) of buffalo sample carried sxt1, stx2, eae and ehlyA genes simultaneously.

CONCLUSION

It was concluded that healthy adult sheep and buffalo are possibly essential carriers of STEC O157. However, rfbE O157 isolate of buffalo RAJ sample carried 4 STEC virulent genes, hence considered an important source of STEC infection to humans and environment which should need to devise proper control systems.

Size Matters: Biological and Food Safety Relevance of Leaf Damage for Colonization of Escherichia coli O157:H7 gfp

This study examined the biological and food safety relevance of leaf lesions for potential invasion of food pathogens into the plant tissue (internalization). This was done by determining the role of artificial leaf damage in terms of damaged leaf area on proliferation of E. coli O157:H7 gfp+. In a two-factorial experiment, unwashed fresh baby leaf spinach (Spinacia oleracea L.) was subjected to four damage levels (undamaged, low, moderate, high damage; factor 1) and three incubation intervals (0, 1, 2 days post-inoculation; factor 2). Individual leaves were immersed for 15 s in a suspension loaded with E. coli O157:H7 gfp+ (10⁶ CFU × mL^–1). The leaves were analyzed individually using image analysis tools to quantify leaf area and number and size of lesions, and using confocal laser scanning and scanning electron microscopy to visualize leaf lesions and presence of the introduced E. coli strain on and within the leaf tissue. Prevalence of E. coli O157:H7 gfp+ was assessed using a culture-dependent technique. The results showed that size of individual lesions and damaged leaf area affected depth of invasion into plant tissue, dispersal to adjacent areas, and number of culturable E. coli O157:H7 gfp+ directly after inoculation. Differences in numbers of the inoculant retrieved from leaf macerate evened out from 2 days post-inoculation, indicating rapid proliferation during the first day post-inoculation. Leaf weight was a crucial factor, as lighter spinach leaves (most likely younger leaves) were more prone to harbor E. coli O157:H7 gfp+, irrespective of damage level. At the high inoculum density used, the risk of consumers’ infection was almost 100%, irrespective of incubation duration or damage level. Even macroscopically intact leaves showed a high risk for infection. These results suggest that the risk to consumers is correlated with how early in the food chain the leaves are contaminated, and the degree of leaf damage. These findings should be taken into account in different steps of leafy green processing. Further attention should be paid to the fate of viable, but non-culturable, shiga-toxigenic E. coli on and in ready-to-eat leafy vegetables.

An Overview of Shiga-Toxin Producing Escherichia coli Carriage and Prevalence in the Ovine Meat Production Chain

Shiga-toxin producing Escherichia coli (STEC) are zoonotic foodborne pathogens that are capable of causing serious human illness. Ovine ruminants are recognized as an important source of STEC and a notable contributor to contamination within the food industry. This review examined the prevalence of STEC in the ovine food production chain from farm-to-fork, reporting carriage in sheep herds, during abattoir processing, and in raw and ready-to-eat meats and meat products. Factors affecting the prevalence of STEC, including seasonality and animal age, were also examined. A relative prevalence can be obtained by calculating the mean prevalence observed over multiple surveys, weighted by sample number. A relative mean prevalence was obtained for STEC O157 and all STEC serogroups at multiple points along the ovine production chain by using suitable published surveys. A relative mean prevalence (and range) for STEC O157 was calculated: for feces 4.4% (0.2-28.1%), fleece 7.6% (0.8-12.8%), carcass 2.1% (0.2-9.8%), and raw ovine meat 1.9% (0.2-6.3%). For all STEC independent of serotype, a relative mean prevalence was calculated: for feces 33.3% (0.9-90.0%), carcass 58.7% (2.0-81.6%), and raw ovine meat 15.4% (2.7-35.5%). The prevalence of STEC in ovine fleece was reported in only one earlier survey, which recorded a prevalence of 86.2%. Animal age was reported to affect shedding in many surveys, with younger animals typically reported as having a higher prevalence of the pathogen. The prevalence of STEC decreases significantly along the ovine production chain after the application of postharvest interventions. Ovine products pose a small risk of potential STEC contamination to the food supply chain.

Pathogenic potential of Escherichia coli O157 and O26 isolated from young Belgian dairy calves by recto-anal mucosal swab culturing

AIMS

The purpose of this study was to investigate the occurrence of Escherichia coli O157 and O26 on Belgian dairy cattle farms, the presence of virulence genes in the confirmed isolates and the association of E. coli O26 presence with calf diarrhoea.

METHODS AND RESULTS

In total, 233 recto-anal mucosal swabs (RAMS) were obtained from healthy and diarrheic dairy calves on three farms, each alternately visited three consecutive times. RAMS were analysed for presence of E. coli O157 and O26, and stx1, stx2 and eae virulence genes. Overall, 19% of RAMS tested positive for E. coli O157, while 31% tested positive for E. coli O26. The majority of isolates possessed both stx and eae, denoting a high pathogenic potential to humans. While both serogroups persisted at farm level, persistence within the same animal over time appeared to be relatively rare. Interestingly, E. coli O26 was already abundantly present at a younger age compared to E. coli O157. Calf diarrhoea could not be associated with presence of E. coli O26.

CONCLUSIONS

Young dairy calves are important on-farm reservoirs of potentially pathogenic E. coli O157 and O26. A role of E. coli O26 in calf diarrhoea could not be confirmed.

SIGNIFICANCE AND IMPACT OF THE STUDY

O157 and O26 are responsible for the majority of human STEC infections. Gaining more epidemiological information regarding their occurrence and persistence on cattle farms will contribute to a better understanding of STEC ecology and risk of human transmission.

Prevalence and serotypes of Shiga toxin-producing Escherichia coli (STEC) in dairy cattle from Northern Portugal

The prevalence of Shiga toxin (Stx)-producing Escherichia coli (STEC) was determined by evaluating its presence in faecal samples from 155 heifers, and 254 dairy cows in 21 farms at North of Portugal sampled between December 2017 and June 2019. The prevalence of STEC in heifers (45%) was significantly higher than in lactating cows (16%) (p<0.05, Fisher exact test statistic value is <0.00001). A total of 133 STEC were isolated, 24 (13.8%) carried Shiga-toxin 1 (stx1) genes, 69 (39.7%) carried Shiga-toxin 2 (stx2) genes, and 40 (23%) carried both stx1 and stx2. Intimin (eae) virulence gene was detected in 29 (21.8%) of the isolates. STEC isolates belonged to 72 different O:H serotypes, comprising 40 O serogroups and 23 H types. The most frequent serotypes were O29:H12 (15%) and O113:H21 (5.2%), found in a large number of farms. Two isolates belonged to the highly virulent serotypes associated with human disease O157:H7 and O26:H11. Many other bovine STEC serotypes founded in this work belonged to serotypes previously described as pathogenic to humans. Thus, this study highlights the need for control strategies that can reduce STEC prevalence at the farm level and, thus, prevent food and environmental contamination.

Identification of Shigatoxigenic and Enteropathogenic Escherichia coli Serotypes in Healthy Young Dairy Calves in Belgium by Recto-Anal Mucosal Swabbing

Enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli (EPEC), and Shigatoxigenic E. coli (STEC) are carried by healthy adult cattle and even more frequently by young calves in their intestinal tract, especially at the height of the recto-anal junction. The purpose of the present study was to assess the presence of ten EHEC, EPEC, and/or STEC O serotypes (O5, O26, O80, O103, O111, O118, O121, O145, O157, and O165) in calves sampled via recto-anal mucosal swabs (RAMS) at three dairy farms in Belgium. A total of 233 RAMS were collected on three consecutive occasions from healthy <6-month-old Holstein-Friesian calves and submitted to a PCR targeting the eae, stx1, and stx2 genes after non-selective overnight enrichment growth. The 148 RAMS testing positive were streaked on four (semi-)selective agar media; of the 2146 colonies tested, 294 from 69 RAMS were PCR-confirmed as EHEC, EPEC, or STEC. The most frequent virulotype was eae+ EPEC and the second one was stx1+ stx2+ STEC, while the eae+ stx1+ and eae+ stx1+ stx2+ virulotypes were the most frequent among EHEC. The majority of EHEC (73%) tested positive for one of the five O serotypes detected (O26, O103, O111, O145, or O157) vs. 23% of EPEC and 45% of STEC. Similarly, more RAMS (73%) harbored EHEC isolates positive for those five serotypes compared to EPEC (53%) or STEC (52%). This survey confirms that (i) healthy young dairy calves are asymptomatic carriers of EHEC and EPEC in Belgium; (ii) the carrier state rates, the virulotypes, and the identified O serotypes differ between farms and in time; and (iii) a majority of EPEC belong to so far unidentified O serotypes.

Microbial detection and identification methods: Bench top assays to omics approaches

Rapid detection of foodborne pathogens, spoilage microbes, and other biological contaminants in complex food matrices is essential to maintain food quality and ensure consumer safety. Traditional methods involve culturing microbes using a range of nonselective and selective enrichment methods, followed by biochemical confirmation among others. The time-to-detection is a key limitation when testing foods, particularly those with short shelf lives, such as fresh meat, fish, dairy products, and vegetables. Some recent detection methods developed include the use of spectroscopic techniques, such as matrix-assisted laser desorption ionization-time of flight along with hyperspectral imaging protocols.This review presents a comprehensive overview comparing insights into the principles, characteristics, and applications of newer and emerging techniques methods applied to the detection and identification of microbes in food matrices, to more traditional benchtop approaches. The content has been developed to provide specialist scientists a broad view of bacterial identification methods available in terms of their benefits and limitations, which may be useful in the development of future experimental design. The case is also made for incorporating some of these emerging methods into the mainstream, for example, underutilized potential of spectroscopic techniques and hyperspectral imaging.

Occurrence and characterization of Shiga toxin-producing Escherichia coli (STEC) isolated from Chinese beef processing plants

In order to investigate the prevalence, O serogroup, virulence genes and antibiotic resistance of Shiga toxin-producing Escherichia coli (STEC) in two beef plants in China, a total of 600 samples collected from 6 sites (feces, hide, pre-evisceration carcasses, post-washing carcasses, chilled carcasses and meat, 50 samples per site in each plant) were screened for the existence of Shiga toxin-encoding genes by PCR. STEC strains in positives were isolated and characterized for serogroup and antibiotic sensitivity. The PCR prevalence rate in each site was 45.0%, 31.0%, 14.0%, 13.0%, 9.0% and 18.0%, respectively. Sixteen O serogroups including O157, O146 and O76 which are associated with disease were identified. The existence of both stx₁ and stx₂ genes was the most common among the isolated strains (42.3%). Among the overall 26 isolates, seven and three were resistant to at least three and ten antibiotics, indicating a high antibiotic resistance in STEC strains isolated from the study.

Investigation of the Causes of Shigatoxigenic Escherichia coli PCR Positive and Culture Negative Samples

Molecular methods may reveal the presence of pathogens in samples through the detection of specific target gene(s) associated with microorganisms, but often, the subsequent cultural isolation of the pathogen is not possible. This discrepancy may be related to low concentration of the cells, presence of dead cells, competitive microflora, injured cells and cells in a viable but non-culturable state, free DNA and the presence of free bacteriophages which can carry the target gene causing the PCR-positive/culture-negative results. Shiga-toxigenic Escherichia coli (STEC) was used as a model for studying this phenomenon, based on the phage-encoded cytotoxins genes (Stx family) as the detection target in samples through real-time qPCR. Stx phages can be integrated in the STEC chromosome or can be isolated as free particles in the environment. In this study, a combination of PCR with culturing was used for investigating the presence of the stx1 and stx2 genes in 155 ovine recto-anal junction swab samples (method (a)-PCR). Samples which were PCR-positive and culture-negative were subjected to additional analyses including detection of dead STEC cells (method (b)-PCR-PMA dye assay), presence of Stx phages (method (c)-plaque assays) and inducible integrated phages (method (d)-phage induction). Method (a) showed that even though 121 samples gave a PCR-positive result (78%), only 68 samples yielded a culturable isolate (43.9%). Among the 53 (34.2%) PCR-positive/culture-negative samples, 21 (39.6%) samples were shown to have STEC dead cells only, eight (15.1%) had a combination of dead cells and inducible stx phage, while two samples (3.8%) had a combination of dead cells, inducible phage and free stx phage, and a further two samples had Stx1 free phages only (3.8%). It was thus possible to reduce the samples with no explanation to 20 (37.7% of 53 samples), representing a further step towards an improved understanding of the STEC PCR-positive/culture-negative phenomenon.

Molecular subtyping and clonal relatedness of human and cattle verotoxin-producing Escherichia coli O157:H7 isolates

Verotoxin-producing Escherichia coli O157:H7 is the dominant serotype isolated from patients with hemolytic-uremic syndrome (HUS) and, Argentina has the highest rate of HUS in the world. However, not all O157:H7 isolates have the same ability to infect and cause disease in humans. It has been postulated that O157:H7 strains integrate subpopulations related to the origin and virulence. In order to study the population structure and genetic diversity of VTEC O157:H7 from Argentina, a combination of molecular subtyping methods such as multiple loci VNTR analysis (MLVA), single nucleotide polymorphisms (SNP) and phylogroups assignment were used. According to MLVA, high genetic diversity was found among strains isolated from cattle, humans and food. On the other hand, 92% of the isolates presented the allele tir 255 T > A T and 95% were assigned to phylogroup E. We did not find a significant association between the isolates origin and the allele T presence (P > 0,05) postulated as significantly overrepresented in human isolates. Our results show that human and cattle VTEC O157:H7 isolates from Argentina are a homogeneous group and, although it presents high genetic diversity in relation to their MLVA and virulence profiles, it is not possible to distinguish divergent populations. The presence in all the strains of a high number of T3SS effectors genes and the no association of genetic subtypes with strain source, is an alert about the potential risk in public health that VTEC O157:H7 cattle strains possess and, at less, a partial explication about the high incidence of HUS in Argentina.

A quantitative real time PCR assay to detect and enumerate Escherichia coli O157 and O26 serogroups in sheep recto-anal swabs

A quantitative PCR method is described for the detection and quantification of E. coli O157 and O26 in sheep recto-anal junction swabs. The method incorporated a short enrichment step (5 h) and the use of a developed standard calibration curve relating the real time PCR cycle threshold (Ct) values to the initial concentration of pathogen in the sheep sample.