Abstract
Shiga toxin-producing Escherichia coli (STEC) are zoonotic enteric pathogens 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. A total of 240 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. Serotype O157:H7 isolates with the virulence genes stx2, eae, and ehxA were identified in 40% (26/65) of the recovered isolates from cattle, sheep and chicken feces. Pulse-field gel electrophoresis (PFGE) analysis grouped most O157:H7 isolates into two clusters with 98.6% homology. The use of multiple-locus variable-number tandem repeat analysis (MLVA) differentiated isolates that were indistinguishable by PFGE. Analysis of the allelic diversity of MLVA loci suggested that the O157:H7 isolates from this region were highly related. In contrast to O157:H7 isolates, 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 represented 35.4% (23/65) of the recovered isolates. In particular, 18.5% (12/65) of all the isolates were serotype O75:H8, which 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. Most non-O157 isolates were ehxA-positive (86.5%, 32/37) but only 10.8% (4/37) harbored eae. These findings indicate that zoonotic STEC with genotypes associated with human illness are present in animals on small farms within rural communities in the Culiacan Valley and emphasize the need for the development of control measures to decrease risks associated with zoonotic STEC.
Highlights
Shiga toxin-producing Escherichia coli (STEC) is a group of foodand water-borne pathogens that are known to cause human gastrointestinal illnesses with diverse clinical spectra, ranging from watery and bloody diarrhea to hemorrhagic colitis [1,2]
Disease symptoms result in the life-threatening, hemolytic uremic syndrome (HUS), and it is thought that Shiga toxins (Stx1 and Stx2) are the key virulence factors contributing to the development of HUS
The aim of the present study was to identify both O157 and non-O157 STEC recovered from feces of domestic farm animals in the Culiacan Valley, a region in Northwest Mexico
Summary
Shiga toxin-producing Escherichia coli (STEC) is a group of foodand water-borne pathogens that are known to cause human gastrointestinal illnesses with diverse clinical spectra, ranging from watery and bloody diarrhea to hemorrhagic colitis [1,2]. Recent epidemiological studies have recognized additional non-O157 serogroups, 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 countries of Latin America [3,4,5,6,7]. Epidemiological studies have shown that not all STEC strains producing Stx are clinically relevant. Many of the strains implicated in bloody diarrhea and HUS in humans are eae-positive; eae is recognized as an important risk factor for HUS [1,12]. 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 [16,17]
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