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Abstract

This study investigates whether specific pathogens are more prevalent in retail meat sold by supermarkets compared to locally sourced markets. Ground beef samples were obtained from conventional ‘big box’ supermarkets and from local, farmers’ markets and examined for the presence of two pathogens, Escherichia coli O157,H7 and Salmonella. For the detection of E. coli O157,H7, homogenized meat samples were enriched overnight in modified EC medium with novobiocin. The enriched cultures were selected onto MacConkey agar with sorbitol, cefixime and tellurite. Presumptive positive colonies were subcultured onto tryptic soy agar with yeast extract and further tested for positive indole and motility, and negative oxidase reactions. For Salmonella detection, homogenized meat samples were incubated first in universal pre-enrichment broth, then enriched overnight in Rappaport-Vassiliadis broth, and further plated onto Salmonella selective medium. Presumptive Salmonella colonies were further incubated on triple sugar iron agar and lysine iron agar to confirm glucose fermentation, sulfide production, and lysine decarboxylase. Oxidase assays were conducted on all presumptive strains. Presumptive colonies of both E. coli and Salmonella were subjected to rapid identification assays and serological tests to confirm identity. Isolates were then tested for antibiotic sensitivity using the Kirby-Bauer assay. The presence of E. coli O157 was observed in one sample of meat sourced from a supermarket, and Salmonella was isolated from ground beef purchased from a different retail supermarket. Neither pathogen was detected from ground beef sourced from farmers’ markets. Our preliminary results demonstrate a potential difference in the prevalence of both E. coli O157 and Salmonella species based upon food source.

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