Occurrence of Listeria monocytogenes and Escherichia coli in raw sheep milk from farm bulk tanks in Central Italy

In relation to milk hygiene and safety, the milking phase is considered a critical moment since it represents a probable pathway for the introduction of unwanted microorganisms in the dairy chain. In particular, Listeria monocytogenes (L. monocytogenes) and Escherichia coli ( E. coli ) are known as possible microbial contaminants of raw sheep milk although extensive knowledge regarding their contamination dynamics in sheep farms is still lacking. This study aimed to examine the occurrence and concentration of these microorganisms in milk samples collected from farm bulk tanks in the region of Lazio (Central Italy) and investigate the related risk factors. Over a period of one year, we collected 372 milk samples from 87 sheep farms and administered a questionnaire in order to acquire information regarding relevant farm management variables. The results showed that L. monocytogenes was not present in any of the samples, suggesting that the contamination of sheep bulk tank milk with this pathogen has a low probability. Meanwhile, E. coli was found in almost two thirds of milk samples (61%) but was quantified below 10 2 CFU/ml in most of them (around 75%). Statistical analysis indicated that the presence of E. coli tends to be more probable and counts are significantly higher during the warmest seasons. Unexpectedly, milk collected by hand milking resulted in lower level of contamination. We believe that, although further studies are necessary to clarify some aspects, the reported data contributed to deepen the knowledge about the occurrence of L. monocytogenes and E. coli in raw sheep milk and provided useful data for future risk assessments.