Expression of hes, iha, and tpsA codified in locus of adhesion and autoaggregation and their involvement in the capability of shiga toxin-producing Escherichia coli strains to adhere to epithelial cells.

OBJECTIVES: Shiga toxin-producing Escherichia coli strains LAA-positive are important cause of human infection. The capability to adhere to epithelial cells is a key virulence trait, and genes codified in LAA pathogenicity island could be involved in the adhesion during the pathogenesis of LAA-positive STEC strains. Thus, our objectives were to compare hes-negative and hes-positive STEC strains in their adherence capability to epithelial cells (HEp-2) and to evaluate the expression levels of the hes, iha, and tpsA in the bacteria adhered and non-adhered to HEp-2 cells. These genes are encoded in LAA, and are virulence factors that participate in adhesion and autoaggregation. RESULTS: We could not observe differences between the adhesion of strains but also in the expression level of of hes, iha, and tpsA. Genes encoded in LAA contribute to the adhesion phenotype though the expression of STEC adhesins is a coordinated event that depends not only the strain but also on the environment as well as its genetic background. Therefore, the results of this study suggest that LAA ,the most prevalent PAI among LEE-negative STEC strains, plays a role in pathogenesis.

Molecular and Genetic Characterization of Colicinogenic Escherichia coli Strains Active against Shiga Toxin-Producing Escherichia coli O157:H7.

The objective of this work was to molecularly and genotypically characterize and test the inhibitory activity of six colicinogenic Escherichia coli strains (ColEc) and their partially purified colicins against STEC O157:H7 isolated from clinical human cases. Inhibition tests demonstrated the activity of these strains and their colicins against STEC O157:H7. By PCR it was possible to detect colicins Ia, E7, and B and microcins M, H47, C7, and J25. By genome sequencing of two selected ColEc strains, it was possible to identify additional colicins such as E1 and Ib. No genes coding for stx1 and stx2 were detected after analyzing the genome sequence. The inhibitory activity of ColEc against STEC O157:H7 used as an indicator showed that colicins are potent growth inhibitors of E. coli O157:H7, being a potential alternative to reduce the presence of pathogens of public health relevance.

Caracterización molecular de aislamientos de Escherichia coli productores de toxina Shiga obtenidos en 2 establecimientos ganaderos del Paraguay Caracterización molecular de aislamientos de STEC de ganado bovino paraguayo / Molecular characterization of Shiga toxin producing Escherichia coli isolated from 2 livestock establishments of Paraguay

Resumen Escherichia coli productora de toxina Shiga (STEC) es un patógeno de importancia alimentaria en los humanos, el bovino es su principal reservorio. El objetivo de este estudio fue determinar la portación de STEC en bovinos del Paraguay y analizar el perfil de virulencia y los serotipos de los aislados reunidos. Se estudiaron 197 muestras de hisopado rectal de bovinos y un promedio de 5 a 50 colonias por bovino positivo a genes stx 1 /stx 2. Se amplificaron por PCR los genes stx 1, stx 2, saa, ehxA y eae. El 84,8% de los bovinos resultaron portadores de STEC. Los perfiles de virulencia predominantes fueron stx 2 y stx 2 /saa/ehxA. La serotipificación se realizó por reacciones de aglutinación en 60 aislamientos seleccionados, se encontró un aislamiento del serogrupo O103, capaz de producir infecciones en humanos. Este trabajo muestra los primeros datos de portación de STEC de ganado bovino paraguayo y señala la necesidad de efectuar otros estudios con mayor cobertura territorial, para lograr una visión completa de este fenómeno.

Abstract Shiga toxin-producing Escherichia coli (STEC) is a food-borne pathogen in humans, with cattle being the main reservoir. The objective of this study was to determine the carrying of STEC in Paraguayan bovines and to analyze the virulence profile and serotypes of these isolates. A total of 197 samples of bovine fecal samples and an average of 5 to 50 colonies from stx 1 /stx 2 positive samples were studied. The stx 1 , stx 2 , saa, ehxA and eae genes were amplified by PCR. 84.8% of the cattle were carriers of STEC. The predominant virulence profiles were stx 2 and stx 2 /saa/ehxA. The serotyping was performed by agglutination reactions for 60 selected isolates, resulting in isolation of serogroup O103, which could produce infections in humans. This work shows the first data of STEC carriers in Paraguayan cattle, and indicates the need for other studies with greater territorial coverage for a complete vision of this phenomenon.

[Molecular characterization of Shiga toxin producing Escherichia coli isolated from 2 livestock establishments of Paraguay]. / Caracterización molecular de aislamientos de Escherichia coli productores de toxina Shiga obtenidos en 2 establecimientos ganaderos del Paraguay.

Shiga toxin-producing Escherichia coli (STEC) is a food-borne pathogen in humans, with cattle being the main reservoir. The objective of this study was to determine the carrying of STEC in Paraguayan bovines and to analyze the virulence profile and serotypes of these isolates. A total of 197 samples of bovine fecal samples and an average of 5 to 50 colonies from stx1/stx2 positive samples were studied. The stx1, stx2, saa, ehxA and eae genes were amplified by PCR. 84.8% of the cattle were carriers of STEC. The predominant virulence profiles were stx2 and stx2/saa/ehxA. The serotyping was performed by agglutination reactions for 60 selected isolates, resulting in isolation of serogroup O103, which could produce infections in humans. This work shows the first data of STEC carriers in Paraguayan cattle, and indicates the need for other studies with greater territorial coverage for a complete vision of this phenomenon.

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.

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

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 24h and the quantification of the biofilm carried out at 48h of incubation. These conditions could be used in future studies on biofilm formation.

Antimicrobial Resistance in Class 1 Integron-Positive Shiga Toxin-Producing Escherichia coli Isolated from Cattle, Pigs, Food and Farm Environment.

The aim of this study was to investigate the presence of class 1 integrons in a collection of Shiga toxin-producing Escherichia coli (STEC) from different origins and to characterize pheno- and genotypically the antimicrobial resistance associated to them. A collection of 649 isolates were screened for the class 1 integrase gene (intI1) by Polymerase chain reaction The variable region of class 1 integrons was amplified and sequenced. Positive strains were evaluated for the presence of antimicrobial resistance genes with microarray and for antimicrobial susceptibility by the disk diffusion method. Seven out of 649 STEC strains some to serogroups, O26, O103 and O130 isolated from cattle, chicken burger, farm environment and pigs were identified as positive for intl1. Different arrangements of gene cassettes were detected in the variable region of class 1 integron: dfrA16, aadA23 and dfrA1-aadA1. In almost all strains, phenotypic resistance to streptomycin, tetracycline, trimethoprim/sulfamethoxazole, and sulfisoxazole was observed. Microarray analyses showed that most of the isolates carried four or more antimicrobial resistance markers and STEC strains were categorized as Multridrug-resistant. Although antimicrobials are not usually used in the treatment of STEC infections, the presence of Multridrug-resistant in isolates collected from farm and food represents a risk for animal and human health.

Development of gluten-free muffins utilizing squash seed dietary fiber.

Gluten-free muffins with squash seed flour (SSF) were developed for contribute to reduce nutritional deficiencies and improving the health of the celiac population. Physicochemical and sensory properties of muffins were evaluated. SSF was incorporated at two levels (10 and 20% w/w) in commercial gluten-free premix (control). Incorporation of SSF increased total dietary fiber content, protein and unsaturated fatty acids. The addition of SSF at 10% resulted in a muffin that did not differ significantly from the control muffin; and also that formulations with SSF at 20% caused an increase in the browning index. Browning was favored by the increase of SSF with higher levels of fiber content. Incorporation of SSF at 20% had a significant effect on the textural parameters (firmness and chewiness) of the muffin. Also, both formulations containing SSF showed a higher overall acceptability, particularly muffins with 20% of SSF that rendered the highest scores for sponginess, texture, taste and colour.

First report of the distribution of Locus of Adhesion and Autoaggregation (LAA) pathogenicity island in LEE-negative Shiga toxin-producing Escherichia coli isolates from Argentina.

Shiga toxin-producing Escherichia coli (STEC) are important foodborne pathogens that can cause severe disease. The ability to adhere to epithelial cells is an important virulence trait and pathogenicity islands (PAIs) play an important role. Recently, researchers identified a member of the Heat-resistant agglutinin family and characterized this antigen named Hemagglutinin from Shiga toxin-producing E. coli (Hes). More importantly, they showed that hes and other genes such as iha, pagC and agn43 were integrated in each of the four modules present in the new PAI named Locus of Adhesion and Autoaggregation (LAA) whose presence is associated with severe disease linked to with LEE-negatives STEC. The distribution of LAA among STEC strains isolates from different origins between 2000 and 2015 from cattle, the farm environment, and food and harboring diverse virulence was investigated. The STEC strains were characterized by PCR to detect three modules of LAA and agn43 (as marker of module IV), and phylogenetic groups were determined. LAA was found in 46% of LEE-negative STEC corresponding to serogroups O91, O174, O113, O171, O178, O130 and others. The presence of this PAI is associated with strains harboring stx2 (56%) and belonging to phylogroup B1 (91%). LAA is a novel pathogenicity island associated with strains isolated from Hemolytic Uremic Syndrome cases. Therefore, the results of this study contribute to a better understanding regarding the pathogenicity of this emergent subset of STEC strains harboring LAA as a predictor of virulence of LEE-negative STEC strains.

Detection and Characterization of Salmonella Serotypes in the Production Chain of Two Pig Farms in Buenos Aires Province, Argentina.

The aim of the present study was to determine the prevalence of Salmonella in the pork production chain and to characterize Salmonella isolates. From 764 samples, 35 (4.6%) were positive for Salmonella spp., as determined by biochemical tests and the presence of the invA gene. From these, 2.6, 2.0, 8.8, and 8.0% corresponded to samples collected from farms, slaughterhouses, boning rooms and retail markets, respectively. Salmonella strains were classified into five serotypes and distributed as follows: S. Typhimurium in the pork production chain, S. Kentucky in farms and slaughterhouses, S. Brandenburg in slaughterhouses, S. Livingstone in farms and S. Agona in boning rooms and retail markets. Interestingly, the antimicrobial susceptibility testing indicated that all 35 Salmonella spp.-positive isolates were resistant to at least one antimicrobial agent, and 30 were multidrug-resistant (MDR) and resistant to different classes of antibiotics. The enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) analysis showed clonal relatedness among strains isolated from farms, boning rooms and retail markets. The presence of antibiotic-resistant Salmonella in food poses a potential health hazard to consumers.

Efecto inhibitorio de Lactobacillus spp. sobre bacterias implicadas en enfermedades transmitidas por alimentos / Inhibitory capacity of Lactobacillus spp. against pathogens involved in foodborne diseases

El género Lactobacillus despierta día a día un creciente interés entre microbiólogos y tecnólogos, quienes intentan descubrir nuevas aplicaciones biotecnológicas y propiedades probióticas. El objetivo de este trabajo fue evaluar la capacidad inhibitoria de Lactobacillus spp. frente a patógenos implicados en enfermedades de transmisión alimentaria (ETA), como Escherichia coli O157:H7, Salmonella spp. y Staphylococcus aureus. Para ello se tomaron muestras de las distintas etapas de la cadena productiva porcina. De dichas muestras se aislaron en total 78 cepas bacterianas, de las cuales 27 (34,61%) tuvieron características fenotípicas y genotípicas correspondientes al género Lactobacillus spp.; el 85,18% de ellas presentó capacidad inhibitoria frente a por lo menos una de las cepas patógenas evaluadas. Estos resultados indican que los microorganismos aislados representan una potencial alternativa para inactivar a los patógenos presentes en los alimentos y así brindar alimentos más seguros a los consumidores.

The genus Lactobacillus daily generates a growing interest among microbiologists and technologists, who try to discover new biotechnological applications and probiotic properties. The main goal of this study was to evaluate the inhibitory capacity of Lactobacillus spp. against pathogens (Escherichia coli O157:H7, Salmonella spp., Staphylococcus aureus) involved in foodborne diseases. For this purpose, samples were collected at different stages of the pork production chain. Seventy eight bacterial strains were isolated. Twenty seven (27) of these strains (37.18%) had genotypic and phenotypic characteristics corresponding to Lactobacillus spp. whereas 85.18% of them showed inhibitory capacity. These data showed that the studied strains represent a potential alternative to inactivate foodborne pathogens and thus provide safe food to consumers.

Variation in the Distribution of Putative Virulence and Colonization Factors in Shiga Toxin-Producing Escherichia coli Isolated from Different Categories of Cattle.

Shiga toxin-producing Escherichia coli (STEC) are pathogens of significant public health concern. Several studies have confirmed that cattle are the main reservoir of STEC in Argentina and other countries. Although Shiga toxins represent the primary virulence factors of STEC, the adherence and colonization of the gut are also important in the pathogenesis of the bacteria. The aim of this study was to analyze and to compare the presence of putative virulence factors codified in plasmid -katP, espP, subA, stcE- and adhesins involved in colonization of cattle -efa1, iha- in 255 native STEC strains isolated from different categories of cattle from different production systems. The most prevalent gene in all strains was espP, and the less prevalent was stcE. katP was highly detected in strains isolated from young and rearing calves (33.3%), while subA was predominant in those isolated from adults (71.21%). Strains from young calves showed the highest percentage of efa1 (72.46%), while iha showed a high distribution in strains from rearing calves and adults (87.04 and 98.48% respectively). It was observed that espP and iha were widely distributed throughout all strains, whereas katP, stcE, and efa1 were more associated with the presence of eae and subA with the eae-negative strains. A great proportion of eae-negative strains were isolated from adults -dairy and grazing farms- and from rearing calves -dairy and feedlot-, while mostly of the eae-positive strains were isolated from dairy young calves. Data exposed indicate a correlation between the category of the animal and the production systems with the presence or absence of several genes implicated in adherence and virulence of STEC.

[Inhibitory capacity of Lactobacillus spp. against pathogens involved in foodborne diseases]. / Efecto inhibitorio de Lactobacillus spp. sobre bacterias implicadas en enfermedades transmitidas por alimentos.

The genus Lactobacillus daily generates a growing interest among microbiologists and technologists, who try to discover new biotechnological applications and probiotic properties. The main goal of this study was to evaluate the inhibitory capacity of Lactobacillus spp. against pathogens (Escherichia coli O157:H7, Salmonella spp., Staphylococcus aureus) involved in foodborne diseases. For this purpose, samples were collected at different stages of the pork production chain. Seventy eight bacterial strains were isolated. Twenty seven (27) of these strains (37.18%) had genotypic and phenotypic characteristics corresponding to Lactobacillus spp. whereas 85.18% of them showed inhibitory capacity. These data showed that the studied strains represent a potential alternative to inactivate foodborne pathogens and thus provide safe food to consumers.

α-Galactosides present in lupin flour affect several metabolic parameters in Wistar rats.

The aim of this study is to evaluate the influence of α-galactosides present in a lupin diet on metabolic parameters in growing Wistar rats. Lupin (Lupinus albus) is a rich source of non-digestible carbohydrates called α-galactosides whose beneficial health effects have been widely reported. For our investigation, twenty male Wistar rats were fed with two different diets: control (C) and lupin flour (L) for a 60-day period. The fermentation of these α-galactosides was monitored by measuring the following indicators: changes in the dynamic lactobacilli and enterobacteriaceae population, cecal content pH, generation of short chain fatty acids (SCFA), Ca and P absorption, and serum lipid (triglycerides and cholesterol) contents. The body weight was lower in the L diet than that in the control with significant differences (p < 0.05). The microbial analyses showed an increase of total lactobacilli counts and a decrease of enterobacteriaceae counts in the L diet when compared to the control, with significant differences (p < 0.05). The fermentations of α-galactosides were also confirmed by decrease in pH levels and the formation of relevant SCFA in the cecal content. The total content of SCFA (µmol per g) at the end of the assay period reached values of 13.58 and 3.64 for L and C rats, respectively. This significant increase of total SCFA in the L diet is responsible for a low pH of the cecal content that in turn prevents the growth and development of potentially pathogenic bacteria (p < 0.05). Regarding lipids, serum triglycerides and cholesterol levels were significantly reduced in the case of animals fed with lupin flour with respect to C animals (p < 0.05). Finally, the L rats showed higher values of an apparent Ca absorption percentage and bone volume percentage with respect to the C animals (p < 0.05). All these results confirm that lupin flour which contains α-galactosides could possibly be considered as a functional ingredient with health promoting properties.

From Farm to Table: Follow-Up of Shiga Toxin-Producing Escherichia coli Throughout the Pork Production Chain in Argentina.

Pigs are important reservoirs of Shiga toxin-producing Escherichia coli (STEC). The entrance of these strains into the food chain implies a risk to consumers because of the severity of hemolytic uremic syndrome. This study reports the prevalence and characterization of STEC throughout the pork production chain. From 764 samples, 31 (4.05%) were stx positive by PCR screening. At farms, 2.86% of samples were stx positive; at slaughter, 4.08% of carcasses were stx positive and at boning rooms, 6% of samples were stx positive. These percentages decreased in pork meat ready for sale at sales markets (4.59%). From positive samples, 50 isolates could be characterized. At farms 37.5% of the isolates carried stx1/stx2 genes, 37.5% possessed stx2e and 25%, carried only stx2. At slaughter we detected 50% of isolates positive for stx2, 33% for stx2e, and 16% for stx1/stx2. At boning rooms 59% of the isolates carried stx1/stx2, 14% stx2e, and 5% stx1/stx2/stx2e. At retail markets 66% of isolates were positive for stx2, 17% stx2e, and 17% stx1/stx2. For the other virulence factors, ehxA and saa were not detected and eae gene was detected in 12% of the isolates. Concerning putative adhesins, agn43 was detected in 72%, ehaA in 26%, aida in 8%, and iha in 6% of isolates. The strains were typed into 14 E. coli O groups (O1, O2, O8, O15, O20, O35, O69, O78, O91, O121, O138, O142, O157, O180) and 10 H groups (H9, H10, H16, H21, H26, H29, H30, H32, H45, H46). This study reports the prevalence and characterization of STEC strains through the chain pork suggesting the vertical transmission. STEC contamination originates in the farms and is transferred from pigs to carcasses in the slaughter process and increase in meat pork at boning rooms and sales markets. These results highlight the need to implement an integrated STEC control system based on good management practices on the farm and critical control point systems in the food chain.

Genetic characterization of Shiga toxin-producing Escherichia coli O26:H11 strains isolated from animal, food, and clinical samples.

The Shiga-toxin producing Escherichia coli (STEC) may cause serious illness in human. Here we analyze O26:H11 strains known to be among the most reported STEC strains causing human infections. Genetic characterization of strains isolated from animal, food, and clinical specimens in Argentina showed that most carried either stx 1a or stx 2a subtypes. Interestingly, stx 2a-positive O26:H11 rarely isolated from cattle in other countries showed to be an important proportion of O26:H11 strains circulating in cattle and food in our region. Seventeen percent of the isolates harbored more than one gene associated with antimicrobial resistance. In addition to stx, all strains contained the virulence genes eae-ß, tir, efa, iha, espB, cif, espA, espF, espJ, nleA, nleB, nleC, and iss; and all except one contained ehxA, espP, and cba genes. On the other hand, toxB and espI genes were exclusively observed in stx 2-positive isolates, whereas katP was only found in stx 1a-positive isolates. Our results show that O26:H11 STEC strains circulating in Argentina, including those isolated from humans, cattle, and meat products, present a high pathogenic potential, and evidence that cattle can be a reservoir of O26:H11 strains harboring stx 2a.

Antibiotic resistance and integrons in Shiga toxin-producing Escherichia coli (STEC).

Shiga toxin-producing Escherichia coli (STEC) cause hemorrhagic colitis (HC) and hemolytic-uremic syndrome in humans (HUS). Cattle are the main reservoir of STEC and transmission to humans occurs through contaminated food and water. Antibiotics are used in pig production systems to combat disease and improve productivity and play a key role in the dissemination of antibiotic resistance genes to the bacteria. Integrons have been identified in resistant bacteria allowing for the acquisition and dissemination of antibiotic resistance genes. STEC strains isolated from humans and animals have developed antibiotic resistance. In our laboratory, 21 non-157 STEC strains isolated from pigs were analyzed to detect class 1 and 2 integrons by PCR. Eight carried integrons, 7 of them harbored intl2. In another study 545 STEC strains were also analyzed for the presence of intl1 and intl2 . Strains carrying intl1 belonged to isolates from environment (n = 1), chicken hamburger (n = 2), dairy calves (n = 4) and pigs (n = 8). Two strains isolated from pigs harbored intl2 and only one intl1 / intl2 , highlighting the presence of intl2 in pigs. The selection for multiresistant strains may contribute to the emergence of antibiotic resistant pathogens and facilitate the spreading of the mobile resistance elements to other bacteria.

Antibiotic resistance and integrons in Shiga toxin-producing Escherichia coli (STEC)

Shiga toxin-producing Escherichia coli (STEC) cause hemorrhagic colitis (HC) and hemolytic-uremic syndrome in humans (HUS). Cattle are the main reservoir of STEC and transmission to humans occurs through contaminated food and water. Antibiotics are used in pig production systems to combat disease and improve productivity and play a key role in the dissemination of antibiotic resistance genes to the bacteria. Integrons have been identified in resistant bacteria allowing for the acquisition and dissemination of antibiotic resistance genes. STEC strains isolated from humans and animals have developed antibiotic resistance. In our laboratory, 21 non-157 STEC strains isolated from pigs were analyzed to detect class 1 and 2 integrons by PCR. Eight carried integrons, 7 of them harbored intl2. In another study 545 STEC strains were also analyzed for the presence of intl1 and intl2. Strains carrying intl1 belonged to isolates from environment (n = 1), chicken hamburger (n = 2), dairy calves (n = 4) and pigs (n = 8). Two strains isolated from pigs harbored intl2 and only one intl1/intl2, highlighting the presence of intl2 in pigs. The selection for multiresistant strains may contribute to the emergence of antibiotic resistant pathogens and facilitate the spreading of the mobile resistance elements to other bacteria.

[Survival of VTEC O157 and non-O157 in water troughs and bovine feces]. / Supervivencia de VTEC O157 y no-O157 en agua de bebederos y materia fecal de bovinos.

Verotoxin-producing Escherichia coli (VTEC) is the etiologic agent of hemolytic-uremic syndrome (HUS), which typically affects children ranging in age from six months to five years old. Transmission is produced by consumption of contaminated food, by direct contact with animals or the environment and from person to person. In previous studies we determined that the environment of a dairy farm is a non-animal reservoir; thus, we proposed to study the survival of 4 VTEC isolates (O20:H19; O91:H21; O157:H7 and O178:H19) in sterile water troughs and bovine feces by viable bacteria count and detection of virulence genes by PCR. It was demonstrated that the survival of different VTEC isolates (O157 and non-O157) varied in terms of their own characteristics as well as of the environmental conditions where they were found. The main differences between isolates were their survival time and the maximal counts reached. The competitive and adaptive characteristics of some isolates increase the infection risk for people that are visiting or working on a farm, as well as the risk for reinfection of the animals and food contamination.