Occurrence of Listeria monocytogenes, Salmonella spp., Escherichia coli and E. coli O157:H7 in vegetable salads

Abstract

The occurrence of Listeria monocytogenes, Salmonella spp., Escherichia coli and E. coli O157:H7 in 63 vegetable salads served at 31 food service facilities (four supermarkets, 14 fast food chain restaurants, and 13 family restaurants) was examined. Homogenized salad samples were incubated in half-strength TSB for 6 h, then in specific selective enrichment media for each bacterial species. After cultures were streaked onto sets of selective agar plates, bacterial colonies with characteristic features were confirmed biochemically and immunologically. Escherichia coli was detected in eight salad samples and L. monocytogenes in one sample. The contaminated salads were purchased from one supermarket, two fast food chain restaurants and two family restaurants tested. Vegetable salads served in the other 26 food service facilities contained none of the four pathogens. Therefore, the production and maintenance of safe, quality vegetable salads in supermarkets, family restaurants and fast food chain restaurants is achievable.