Incidence and coincidence of Listeria spp., motile aeromonads and Yersinia enterocolitica on ready-to-eat fleshfoods

A survey for the presence of Listeria spp., Yersinia enterocolitica and motile aeromonads in 203 samples of ready-to-eat fleshfoods purchased from retail outlets was conducted. Overall, 39.4%, 3.4% and 23.2% of samples were positive for the presence of Listeria spp., Y. enterocolitica and motile aeromonads respectively. Two factors have been identified as contributing to contamination of fleshfoods by these cold-tolerant bacteria. These are (i) the method of sale; delicatessen-bought foods were notably more contaminated than similar products bought pre-packaged, and (ii) the method of preservation. For motile aeromonads fermented foods were the least contaminated, whereas smoked and cooked products had similar incidence rates. For L. monocytogenes, significantly more (41.9%) smoked products were contaminated than fleshfoods preserved by other methods. For Y. enterocolitica, only cooked products were contaminated. In the case of cooked fleshfoods it must be assumed that most contamination occurs post-cooking and that contamination rates are increased by poor food handling procedures. Of the three possible pairwise combinations of these organisms, the coincidence of Y. enterocolitica and motile aeromonads was the only one that differed significantly from a random distribution (P less than 0.001), indicating that fleshfoods contaminated with Y. enterocolitica are probably also contaminated by motile aeromonads.