Listeria in food

: Since some outbreaks of listeriosis have been traced to various foods, the contamination rate of the foodstuffs is of great interest. Out of 1708 samples of milk and milk products, 105 samples (6.1%) proved to contain Listeria spp. L. monocytogenes was isolated from 54 specimens (3.0%). The isolation rate among 496 samples of meat and raw meat products was 38.9%. L. monocytogenes was found in 14.1% of these samples. Salads and vegetables proved to be contaminated by Listeria spp. in 6.4%; 2.1% of the strains were identified as L. monocytogenes. 57.4% of food samples contained less than 10 Listeria spp. per gram, while in the other samples the Listeria count ranged between 10 and 10(3)/g. In only one sample of cheese was more than 10(3) Listeria/g found. In contrast to cheese, where the contamination normally occurs during the ripening process and must be considered a hygiene problem, meat is already contaminated during slaughtering and processing. Beside these findings, there are further differences in the listerial microbiology of cheese and raw meat products. Additional studies are needed to determine the bearing of these factors on the epidemiology of human listeriosis.