Serovars of Listeria monocytogenes and Listeria innocua from food.

The increase of listeriosis outbreaks in recent years has mainly been due to the consumption of contaminated dairy products. This prompted a revision of prevention and control measures. Cheese and other foods (meat, poultry meat) were investigated. For isolation, samples were prepared and investigated according to the recommendations of the FDA with some modifications including, in particular, sub-enrichment. Suspicious colonies were tested biochemically followed by serological identification with factor sera. Out of 100 chicken (95 broilers, 5 layers) Listeria monocytogenes was isolated from 85 carcases. The contamination rate for minced beef and pork (n = 76) was approximately 30%. That for selected ripened soft cheeses (n = 89) was 9%. The counts of Listeria in red meat were usually very low (approximately 10/g). Serovar 1/2a was predominant (78 out of 102 strains). Further serovars detected were: 1/2b, 1/2c, 3a, 4a, 4b, 4d. For comparison, isolated strains of L. monocytogenes and Listeria innocua were inoculated into chicken embryos. In contrast to the former, L. innocua did not kill the embryos.