Modelling the dynamics of coagulase-positive staphylococci in artisanal raw milk cheese during ripening: Influence of microbiological and intrinsic factors

The aim of this study was to model the population of coagulase-positive staphylococci in an artisanal raw milk cheese, throughout the ripening period, to assess which microbiological and intrinsic parameters influence the dynamic of coagulase-positive staphylococci counts along the production process. Coagulase-positive staphylococci were enumerated in 144 samples through a longitudinal sampling of 12 batches of raw milk cheese produced at the same processing plant, using raw milk supplied by two dairy cattle farms. The samples tested were raw milk and raw milk cheese after 7, 45 and 90 days of ripening. The 354 colonies randomly collected from the enumerated samples were identified as Staphylococcus aureus. The model outputs showed that the initial coagulase-positive staphylococci population in raw milk represents the primary driver influencing the dynamics of coagulase-positive staphylococci counts throughout the production process, up to the end of ripening period. The model further showed that a one unit increase in pH during production resulted in a 16.73% increase in coagulase-positive staphylococci Log10 counts in the overall production. In contrast, a 1 Log10 increase of Lactic Acid Bacteria counts along the process corresponded to only a limited increase in coagulase-positive staphylococci Log10 values. The outputs of the model highlight the critical importance of monitoring the coagulasepositive staphylococci counts in raw milk and the cheese pH to limit the growth of coagulase-positive staphylococci throughout the raw milk cheese production process.