Listeria monocytogenes in raw milk and artificially contaminated aliquots

In Italy cow’s raw milk can be sold in vending machine since 2004 and it could be consider a Ready-To-Eat food. However, raw milk was not exempt from biological hazards, in fact Italian legislation dictated that the statement “to be consumed prior boiling” should be posted on vending machines to protect public health. A brief heat treatment of raw milk could be a higher risk for the public health. Therefore, the European legislation imposed that L. monocytogenesmust not exceed the limit of 100 CFU/mL, corresponding to Food Safety Objective (FSO), for non risk group population, and the absence of the pathogen for the immune-compromised individuals and neonates. This study compares the efficiency of the Surface Spread Plate (SSP) and the Most Probable Number (MPN) techniques in recovering L. monocytogenes from artificially contaminated raw milk samples. Moreover L. monocytogenesis enumerated from raw milk samples using the same techniques and the colony count at 30°C is determined in raw milk purchased from vending machines in Northern Italy. The MPN technique was able to recover L. monocytogenes in the artificially contaminated raw milk aliquots at different times of analysis and for different values of inoculums with a major frequency than the SSP technique. The techniques did not show the same efficiency in recovering L. monocytogenes from artificially contaminated raw milk aliquots. The SSP technique did not always detect concentration of the pathogen that exceed the Food Safety Objective (FSO) (absent in 25 g) for the at risk population groups. The food safety of cow’s raw milk contaminated with low level of L. monocytogenescould not be guaranteed for at risk population when consuming such product. Both techniques reported a similar efficiency in the detection of L. monocytogenes from raw milk aliquots for concentration value higher than 100 CFU/mL and thus above the FSO. However the SSP technique proved to be more efficient in detecting Listeriain cow’s raw milk.