Genotypic analyses of Shiga toxin-producing Escherichia coli O157 and non-O157 recovered from feces of domestic animals in rural farms in Mexico

Authors: AMEZQUITA-LOPEZ, BIANCA - Center For Research In Food And Development (CIAD); Quinones, Beatriz; Cooley, Michael; LEON-FELIX, JOSEFINA - Center For Research In Food And Development (CIAD); CASTRO-DEL CAMPO, NOHELIA - Center For Research In Food And Development (CIAD); Mandrell, Robert; JIMENEZ, MARIBEL - Center For Research In Food And Development (CIAD); CHAIDEZ, CRISTOBAL - Center For Research In Food And Development (CIAD)

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2012
Publication Date: 12/10/2012
Citation: Amezquita-Lopez, B.A., Quinones, B., Cooley, M.B., Leon-Felix, J., Castro-Del Campo, N., Mandrell, R.E., Jimenez, M., Chaidez, C. 2012. Genotypic analyses of Shiga toxin-producing Escherichia coli O157 and non-O157 recovered from feces of domestic animals in rural farms in Mexico. PLoS One. 7(12):e51565. doi:101371/journal.pone.0051565.

Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) is a food- and water-borne pathogen that is known to cause human gastrointestinal illnesses with a diverse clinical spectra, ranging from watery and bloody diarrhea to hemorrhagic colitis. In rare cases, disease symptoms result in the life-threatening, hemolytic uremic syndrome (HUS), and it is thought that production of Shiga toxins (Stx1 and Stx2) are key virulence factors that contribute to the development of HUS. Although more than 200 different serotypes of STEC have been isolated, serotype O157:H7 has been most commonly-associated with HUS in North America. Recent epidemiological studies have recognized additional non-O157 serotypes, including O26, O45, O91, O103,O104, O111, O113, O121, and O145, among STEC strains that were linked to severe human disease in the United States, Europe and parts of Latin America. Epidemiological studies have shown that not all STEC strains producing Stx are clinically relevant. Thus, it is believed that accessory STEC genes may also contribute to human disease. E.coli strains, recovered from animal reservoirs and harboring stx, eae, and/or ehxA genes, are thought to represent a subpopulation of STEC strains that may pose a higher risk to human health. STEC strains have been isolated from a variety of animals, and it is considered that the major carrier for STEC strains is cattle. However, recent evidence has indicated that small domestic ruminants, including sheep and goats, have been implicated as key reservoirs of STEC. In particular, sheep and their products have been documented as reservoirs for STECs with a diverse set of non-O157 serogroups that also harbor genes encoding key virulence factors that have been implicated in human disease. STEC strains can be also carried by other domestic and wild animals, such as cats, dogs, rodents, deer, birds, feral pigs, chickens, and insects. Only few recent studies have examined the prevalence of O157 and non-O157 STEC strains in products derived from animals or in animal fecal samples at various locations in Mexico. In particular, a greater prevalence of E. coli O157 was found in swine feces (2.1%) than cattle feces (1.25%), recovered from eight different large farms localized throughout central Mexico. Furthermore, the presence of O157 as well as non-O157 on beef carcasses was confirmed at slaughter plants in northeast and western Mexico. Surveillance studies recovered non-O157 strains in a large proportion of ready-to eat meals in Mexico City, suggesting that non-O157 could be a potential source of infection in humans. Thus, additional studies are needed on the isolation, sources, and prevalence of STEC strains in other relevant locations in Mexico. To determine relevant animal reservoirs for toxigenic E. coli in Mexico, the present study employed a protocol for the selective enrichment of STEC in feces of domestic animals found in small rural farms within the Culiacan Valley. The Culiacan Valley, located in Northwest Mexico, has large and fertile agricultural fields and a successful packaging industry, known for implementing antimicrobial validations for horticultural commodities (tomatoes, cucumbers, and bell peppers). The rural farms, where sampling was performed in the present study, were located in communities that appear to not follow good agricultural practices and where livestock raising is commonly performed for local consumption within the rural communities. The recovered STEC isolates were further examined for O-and H-antigens and some important virulence factors. Furthermore, the generic relatedness of the isolates were analyzed by employing the genotyping methods pulse-field gel electrophoresis (PFGE) and multiple-locus variable-number tandem repeat analysis (MLVA) to obtain a better understanding of the geographical distribution and relevant sources of zoonotic STEC in the Culiacan V

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) is a zoonotic enteric pathogen associated with human gastroenteritis worldwide. Cattle and small ruminants are important animal reservoirs of STEC. The present study investigated animal reservoirs for STEC in small rural farms in the Culiacan Valley, an important agricultural region located in Northwest Mexico. Fecal samples from domestic animals were collected from five sampling sites in the Culiacan Valley and were subjected to an enrichment protocol followed by either direct plating or immunomagnetic separation before plating on selective media. erotype O157:H7 was identified in 40% of the recovered E. coli isolates from cattle, sheep and chicken feces with the virulence genes stx2, eae, and ehxA. Pulse-field gel electrophoresis (PFGE) analysis demonstrated that most O157:H7 isolates grouped into two clusters with 98.6% homology. The use of multiple-locus variable-number tandem repeat analysis (MLVA) allowed the discrimination of isolates that were indistinguishable by PFGE. Analysis of the allelic diversity of 10 MLVA loci suggested that the O157:H7 isolates from this region were highly related. Furthermore, a greater genotypic diversity was observed in the non-O157 isolates, resulting in 23 PFGE types and 14 MLVA types. The relevant non-O157 serotypes O8:H19, O75:H8, O111:H8 and O146:H21 were identified in 35% of the STEC isolates. In particular, serotype O75:H8, detected in 32 % of the non-O157 isolates, was the most variable serotype by both PFGE and MLVA. The non-O157 isolates were predominantly recovered from sheep and were identified to harbor either one or two stx genes additionally, most non-O157 isolates were positive for ehxA and/or eae genes. These findings have indicated the prevalence of zoonotic STEC with genotypes associated with human illness in small farms within rural communities in the Culiacan Valley and have provided relevant information for the development of on-farm control measures of risk factors associated with zoonotic STEC.