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United States Department of Agriculture

Agricultural Research Service

Research Project: Molecular Biology of Human Pathogens Associated with Food

Location: Produce Safety and Microbiology Research

Title: Genotypic Characterization of Shiga Toxin-Producing Escherichia coli (STEC) Strains Recovered from Farm Animal Feces in Mexico

Authors
item Amezquitq-Lopez, B.A. -
item Quiñones, Beatriz
item Leon-Felix, J. -
item Castro Del Campo, N. -
item Martinez, C. -
item Gaxiola, M.G. -
item Lugo-Celchor, Y. -
item Chaidez, C. -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 28, 2011
Publication Date: N/A

Technical Abstract: Technical Abstract and Interpretive Summary: Provide electronically in Word. Sixty-three strains of Shiga toxin-producing Escherichia coli (STEC) were recovered from farm animal feces in distinct regions in the Culiacan Valley, an important agricultural region in Mexico for horticultural crops that are exported to the United States. The aim of the present study was to characterize the genetic composition of STEC strains in the Culiacan Valley by identifying different virulence determinants that code for adhesins, proteases, cytotoxins, and effectors and that are considered to be necessary for STEC strains to be pathogenic. The isolation and identification of STEC strains were performed using immunomagnetic separation, culturing methods and polymerase chain reaction (PCR). The strains were analyzed by using PCR with sequence-specific primers to determine the presence of genes encoding intimin (eae), enterohemolysin (ehxA), serine protease (espP), catalase peroxidase (katP), the type II secretion system (etpD), subtilase cytotoxin (subA), autoagglutinating adhesion (saa), type III secreted effectors encoded in the genomic islands OI-122 (ent/espL2), Ol-71 (nleH1-2 and nleA) and the distinct variants of Shiga toxin (stx1, stx1c, stx1d, stx2, stx2c, stx2d, stx2act, stx2e, stx2f, stx2g). STEC strains were analyzed using a Vero cell line (Vero-d2EGFP) that produced a fluorescent signal to monitor the activity of Shiga toxin. The results from the PCR analysis showed that strains were positive for the following genes: 57 (90.5%) for ehxA, 33 (52.4%) for espP and stx2c genes, 32 (50.8%) for eae gene, 30 (47.6%) for ent/espL2 and nleH1-2 genes, 28 (44.4%) for etpD, katD and per genes, 27 (42.9%) for stx1, 25 (39.7%) for nleA gene, 24 (38.1%) for stx1c, 23 (36.5%) for stx2d gene, 5 (7.9%) for saa, subA and stx2 genes and 3 (4.8%) for stx2dact gene. The activity of Shiga toxins on Vero-d2EGFP showed 27.9% strains with high activity (0=20% of EGFP signal), 24.6% with moderate activity (20=40%) and 47.5% low activity (40=70%). In conclusion, the STEC strains, recovered from agricultural regions in the Culiacan´s Valley, were found to be diverse in their genetic composition, and this analysis proved to be an important evaluation of the prevalence and risks of pathogenic E. coli in food production environments.

Last Modified: 9/1/2014
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