ARS | Publication request: Distinct PFGE and MLVA Genotypes of Shiga Toxin-Producing Escherichia coli (STEC)Recovered from Feces of Farm Animals in the Culiacan Valley, Mexico(Abstract)

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 23, 2012
Publication Date: N/A

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) is a food- and water-borne pathogen that is known to cause human gastrointestinal illnesses. The major reservoirs for STEC are sheep and cattle feces. This study investigated the prevalence and genetic diversity of STEC genotypes from animal feces of rural farms near the rivers of the Culiacan Valley, northwestern region of Mexico. Methods: Animal feces were collected during one year of sampling. Two different isolation methods were used to recover STEC strains. The first sampling method was without immunomagnetic separation (IMS) and the second one was with IMS. The strains were examined by PCR for presence of O-antigen, H-antigen, intimin (eae), enterohemolysin (ehxA), Shiga toxin 1 (stx1) and Shiga toxin 2 (stx2) genes, associated with human illness. Also, the genomic diversity of STEC strains was assessed by pulse-field gel electrophoresis (PFGE) and multi-locus variable-number-tandem-repeat analysis (MLVA). Results: Sixty-five STEC strains were recovered from cattle, sheep and chicken feces in several farms within distinct regions in the Culiacan Valley. The results showed that 40% of the strains belonged to serotype O157:H7 and were positive for genes stx2, eae and ehxA. Twenty-six E. coli O157:H7 strains were characterized by MLVA, revealing 8 unique MLVA types when compared to only 5 PFGE types with more than 90% of similarity. Other serotypes were isolated that could be considered as important human pathogens. E. coli O111:H8 (3%) and serogroup O8 (H19 and H?) (9.2%) were detected in cattle and sheep feces; these strains also harbored stx1, eae and ehxA virulence genes. Other serotypes not linked to human disease were also isolated. The 37 non-O157 STEC strains were genotyped into 14 different MLVA types; however, the PFGE analysis for non-O157 STEC strains identified 23 types with a 60% similarity. Conclusions: STEC strains with serotypes and virulence genes linked to human illness were identified in animal feces in the Culiacan Valley. Sheep feces were more a significant source for isolation of STEC strains in this region. In contrast to discrimination of MLVA compared to PFGE analysis of genomic diversity of O157:H7 strains, the examination of non-O157 strains by MLVA was less discriminating than PFGE for genotyping