Listeria monocytogenes and lactic acid bacteria - Current investigations on the occurrence in prepackaged meat products stored under refrigeration

Listeria were isolated in 5% (4 out of 78) of ready-to-eat retail meat prod ucts which, after pasteurization, had been sliced, prepackaged and stored u nder refrigeration until one week after the end of the indicated "best befo re" date on the package. Two Of the Listeria-positive samples were Bologna- type sausages, one was cooked turkey breast, and one was cooked pork ham. A ll positive samples contained less than 100 listeria/g, but were contaminat ed in all cases with Listeria monocytogenes (L.m.). Genetic fingerprints of the L.m, strains, produced by BOX-rep-APD, showed that three samples conta ined one genotype each while one sample contained two genotypes. Two sample s contained a genotype which can be grouped to a BOX-rep-APD-Cluster domina ted by the L.m. serovar 4b. The pH values of the products were in most case s 5.2 to 5.8. The number of lactic acid bacteria (LAB) exceeded 10(8)/g in the majority of the samples. Phenotypic and genotypic characterization of r epresentative LAB isolates of selected samples showed that the dominant LAB microflora consisted of Lactobacillus sakei (54% of the samples), Leuconos toc carnosum (23%), Lactobacillus curvatus (15%), Weissella viridescens (8% ) and Carnobacterium piscicola (8%) for all samples containing at least 10( 5) LAB/g.