Occurrence of Listeria monocytogenes and Escherichia coli in Raw Sheep's Milk from Farm Bulk Tanks in Central Italy.

ABSTRACT: For milk hygiene and safety, the milking phase is a critical moment because it is a probable pathway for the introduction of unwanted microorganisms in the dairy chain. In particular, Listeria monocytogenes and Escherichia coli are known as possible microbial contaminants of raw sheep's milk, although extensive knowledge regarding their contamination dynamics on 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 to investigate the related risk factors. Over a period of 1 year, we collected 372 milk samples from 87 sheep farms and administered a questionnaire to acquire information regarding relevant farm management variables. L. monocytogenes was not found in any of the samples, which indicates a low occurrence of this pathogen in sheep's bulk tank milk. In contrast, E. coli was found in almost two-thirds of milk samples (61%) but at levels below 102 CFU/mL in most of them (approximately 75%). Statistical analysis indicated that, during the warmest seasons, E. coli presence is more probable and counts are significantly higher. Unexpectedly, milk collected by hand milking had a lower level of contamination. Although further studies are necessary to clarify some aspects, the reported data add to the knowledge about the occurrence of L. monocytogenes and E. coli in raw sheep's milk and will be useful for future risk assessments.

Sheep Milk Yogurt from a Short Food Supply Chain: Study of the Microbiological, Chemico-Physical and Organoleptic Parameters in Relation to Shelf-Life.

Aim of this work was to analyse some microbiological, chemico-physical and organoleptic parameters of sheep milk yogurt during and after its declared shelf-life. Five samples of a sheep's milk yogurt of the same lot, collected from a short supply chain ovine dairy farm of the Roman province, were analysed. Declared shelf-life of the product was 30 days. The products were examined at 2, 14, 30, 35 and 40 days from the production date, performing the following microbiological analyses: enumeration of i) colony-forming units characteristic of the yogurt, ii) Enterobacteriaceae, iii) yeasts and/or moulds at 25°C. Microbiological identification was performed by miniature biochemical tests and for the lactic acid bacteria also by PCR. At every test interval, evaluation of organoleptic parameters and pH was also performed. The analysed product maintained an almost constant amount of lactic acid bacteria until the end of the declared shelf-life. Concerning lactic acid bacteria, a 100% concordance of the results observed by using biochemical identification methods and PCR assays was obtained. After 14 days from the production, the presence of yeasts (Candida famata) was revealed, while the presence of moulds was detected after 30 days. Ralstonia picketii, an environmental microorganism, was also isolated. The results obtained in this study indicate that yogurt spoilage is mainly due to the growth of specific microorganisms of spoilage, such as yeasts and moulds.