Behaviour and adhesion capacity of Listeria monocytogenes on Mozzarella di Bufala Campana PDO cheese and in fluids involved in the production process

Listeria monocytogenes is a foodborne pathogen for humans. It can be found in ready-to-eat (RTE) products and its presence represents one of the biggest food safety concerns. Most of the cases of cheese contamination reported by the Rapid Alert System for Food and Feed (RASFF) in the last 10 years did not involve Mozzarella di Bufala Campana (MBC) Protected Designation of Origin (PDO) cheese. Suddenly, in the last years, RASFF has disposed of the withdrawn from the market of this product contaminated with L. monocytogenes on two different occasions (RASFF 2018/1198 and 2018/2459), and the Canadian Food Inspection Agency disposed one withdrawn in 2019. Following these events, this study aimed to evaluate the behaviour of L. monocytogenes in Mozzarella di Bufala Campana PDO cheese. First of all, the adhesion capacity of the pathogen to MBC cheese was studied through microbial challenge tests simulating the passage of MBC in hardening water and in covering liquid used for cheese storage during the production process. In addition, the ability of L. monocytogenes to grow in MBC cheese and covering liquid during shelf life, at refrigerated condition, was evaluated also this time employing microbial challenge tests. Results demonstrated that L. monocytogenes can adhere to the surface of the cheese and be released during the contact of contaminated cheese with other fluids. However, the presence of an abundant microbiota on the cheese exerted a protective role against this pathogen preventing the growth of L. monocytogenes. Indeed, the pathogens artificially contaminating the covering liquid at 2 log CFU/mL and 4 log CFU/mL remained at the inoculum level during 32 days of storage at 4 °C.