Detection and characterization of foodborne pathogens on bison carcasses

Bison meat is a relatively new, emerging meat species gaining increased popularity in the U.S. and European meat markets, but little is known regarding the microbiological safety of bison meat. The present study evaluated contamination of bison with Salmonella spp., Listeria spp., and Escherichia coli/Escherichia coli O157:H7, as well as their associated resistance and pathogenesis factors to estimate the potential risk of bison meat to the consumer. The results of our study indicate that bison meat may not be a significant source of foodborne pathogens compared to other meat species, with an overall prevalence of 18.3% for Listeria spp, 38.3% for Escherichia coli, 1.13% for E. coli O157:H7, and 3.94% for Salmonella spp. PCR analysis indicated that E. coli O157:H7 and Salmonella isolates possessed virulence properties that may pose a potential health risk to consumers. Although bison is not subjected to subtherapeutic antibiotics and hormones, resistance to a number of antimicrobial agents was observed in these microorganisms. Tetracycline was one of the most prevalent resistance traits among isolates tested. However, the antimicrobial resistance level in microorganisms from bison was generally lower than that reported in other animal species, especially to drugs commonly used for the treatment of human disease, indicating the beneficial impacts of antimicrobial-free feeding practice on reducing antimicrobial resistance. Vectors of antimicrobial resistance, such as plasmids, class 1 integrons or transposons, and antimicrobial resistant genes, were also found in these pathogens. Conjugation studies showed that most of these detected resistance genes could be donated to other bacteria, indicating a potential risk to human consumers. The growth and survival of E. coli O157:H7 was also investigated on whole pieces and minced bison meat at 5°C and 10°C. The results were similar to those reported in beef, which may be due to their similar pH values and background microorganism species. The data generated in our studies will also provide useful data for the development of mathematical models of E. coli O157:H7 bison meat and other food matrices and useful baseline information for further research.