Escherichia coli O157 in Ground Beef from Local Retail Markets in Pachuca, Mexico

Abstract

Escherichia coli O157 strains have been recognized as pathogenic bacteria, of which raw beef is a known vehicle. An evaluation was done of the presence of E. coli O157 in ground beef from local retail markets in Pachuca, Hidalgo State, Mexico. A total of 120 ground beef samples (500 g) were tested for E. coli O157 by simultaneous application of the U. S. Department of Agriculture, Food Safety and Inspection Service (FSIS)'s Microbiology Laboratory Guidebook culture procedure 5.05, and two commercial kits, Reveal for E. coli O157:H7 and Visual Immunoprecipitate Assay (VIP) Gold for enterohemorrhagic E. coli. Two incubation times (8 and 20 h) were used with the commercial kits. Presence of stx1, stx2, and eaeA loci was determined by multiplex PCR. Of 360 subsamples (120 per procedure), 12 samples were found to be E. coli O157 positive by the FSIS culture method. With VIP, 73 subsamples were presumptive positive after 8 h of enrichment, and 60 were presumptive positive after 20 h of enrichment. Of these, only 6 (8 h) and 8 (20 h) subsamples were confirmed true positives with the FSIS method. With Reveal, 60 subsamples were presumptive positive after 8 h of enrichment and 50 were presumptive positive after 20 h of enrichment. Of these, only 6 (8 h) and 8 (20 h) subsamples were confirmed as true positives with the FSIS method. A total of 57 E. coli O157:H7 and 21 E. coli O157 strains were isolated. None of the O157 or O157:H7 strains had stx1 or stx2 loci, and only one had the eaeA locus. To our knowledge, this is the first report of the presence of E. coli O157 in commercial ground beef from Mexico, and the first report of isolation of a large number of stx-negative E. coli O157 and E. coli O157:H7 strains in Mexico.

Variation in Heat and Pressure Resistance of Verotoxigenic and Nontoxigenic Escherichia coli

“…E. coli 0157 is the most commonly reported serotype of VTEC in North America; however, not all E. coli 0157 isolates harbor genes coding for Stx (22,25,53). Moreover, VTEC of other serotypes (non-0157 VTEC) cause 50% or more of VTEC illness in the United States and Canada (5,13,48).…”

Frecuencia de contaminación y de serotipos de Salmonella enterica y Escherichia coli en una operación integrada de matanza y deshuese de bovinos

“…Estos hallazgos coinciden con investigaciones previas (13) en las que se detectaron serovariedades (O157 y no O157) asociadas con cepas STEC (n= 146), pero sólo dos de éstas portaban los factores de virulencia característicos. Esta tendencia se mantiene en estudios posteriores, en los cuales se reportan tasas bajas (<1 %) de contaminación con cepas patógenas de E. coli en canales y carne molida de bovinos en México (9,40,41) . Tal comportamiento podría obedecer a múltiples factores.…”