Mura, Elia (2013) Studio della contaminazione da Listeria monocytogenes in caseifici ovini industriali. Doctoral Thesis.
Listeria monocytogenes (Lm) is the causal agent of listeriosis, a foodborne disease that exhibits a high mortility rate (20-30%).Listeriosis outbreaks are linked to the consumption of ready-to-eat food and some dairy products have been clearly identified as a primary source of infection. Lm post-process contaminations in cheese from thermized/pasteurized milk or in whey cheese can be tracked to the cheese-making plants environment. The present study evaluated Lm prevalence and distribution in sheep’s cheese factories. In two plants located in Sardinia (Italy) were carried-out 7 sampling, representative of seasonal evolution of the production activities. The samples were collected from the environment (570), from Pecorino Romano (PR) rind (47) and Ricotta salata (RS) surface (32 RS). Each sample was analyzed according to ISO 11290-1:2005. PFGE and multiplex PCR serotyping, were carried out on 70 Lm isolates, to track the contaminations to sites from the dairy plants environment. Lm prevalence ranged between 23%-12.4% in samples collected from the environment and 26%-9.5% from PR rind, all RS samples were negative. The most contaminated environmental areas were the washing and the ripening premises. Serotyping generated three serovars: 1/2a, 1/2b, 4b. PFGE analysis allowed to classify the Lm isolates into 8 clusters. The same strains were detected in the PR rind and in the environmental surfaces, suggesting a clear route of contamination for Lm and its niches into dairy plants.
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