Prevalence of Listeria monocytogenes and other listerias in Italian-made soft cheeses.

The frequency of L. monocytogenes and other listerias was determined in different types of Italian-made soft cheeses purchased from retail outlets (shops and supermarkets) located in different areas and different towns of central Italy. Of the 164 examined samples, eight proved to be positive for L. monocytogenes (4.9%), seven strains belonged to serotype 1, and one strain to serotype 4. Thirty-six samples were positive for the presence of other listeria species (22%); of these, L. innocua was prevalent (72% of positive samples). The cheeses bought in supermarkets displayed a higher and statistically significant (Fisher's exact test: 0.0016) positivity for Listeria spp. than those sold by the shops, independently of the type of cheese. One particular type of cheese proved to be frequently contaminated (Fis. ex. test: 0.0013). Technical, analytical and epidemiological aspects are discussed.