Field handling conditions of raw milk sold in vending machines: experimental evaluation of the behaviour of Listeria monocytogenes, Escherichia coli O157:H7, Salmonella Typhimurium and Campylobacter jejuni

The direct sale by farmers of raw milk for human consumption has been allowed in Italy since 2004. The aim of this study was to evaluate the behaviour of selected foodborne pathogens in raw milk sold in vending machines, in field handling conditions, during shelf-life from production to consumption. Temperature of raw milk from 33 farms authorized to produce and sell raw milk were investigated together with consumer habits in one Province of the Emilia-Romagna Region (Northern Italy). Failure to maintain appropriate low temperatures during shelf-life was recorded and 43% of consumers did not boil milk before consumption. Listeria monocytogenes, Escherichia coli O157:H7, Salmonella Typhimurium and Campylobacter jejuni strains were inoculated into raw milk samples, and the best (4°C as fixed by law) and worst temperature storage conditions detected (variable temperature) were simulated. Boiling tests were performed for each pathogen considered at high and low contamination levels. Results showed an increase in L. monocytogenes in milk stored at 4°C and at variable temperatures recorded in shelf-life monitoring, an increase in E. coli O157:H7 and S. Typhimurium at variable temperatures but not at 4°C, and a decrease of C. jejuni in all storage conditions. Milk boiling is effective to make the milk safe for consumers. This study provides evidence that appropriate handling of raw milk maintaining low temperatures and consumer education on boiling raw milk before consumption are key factors in preventing foodborne infections linked to raw milk consumption and contribute to assess the risk of foodborne infection linked to raw milk consumption.