Behavior of four main dairy pathogenic bacteria during manufacturing and ripening of pecorino siciliano cheese

Abstract

Background: Consumption of raw cheese may be associated with different diseases. This study aimed to evaluate behavior of four pathogenic bacteria during manufacture and ripening of Protected Designation of Origin (PDO) Pecorino Siciliano cheese. Methods: The experimental cheese groups were inoculated with pathogenic bacteria, including Escherichia coli O157, Listeria monocytogenes, Salmonella Enteritidis, and Staphylococcus aureus. The cheese making processes were monitored from milk curdling until 3 months ripened cheeses and the levels of Lactic Acid Bacteria (LAB) and the four dairy pathogens were evaluated by plate counts. Randomly Amplified Polymorphic DNA (RAPD)-Polymerase Chain Reaction (PCR) analysis was applied to confirm that the colonies isolated during the several steps of production were the same strains added in milk. Statistical analysis was done using XLStat software. Results: The levels of mesophilic and thermophilic coccus and rod LAB in curd were comparable in both trials and reached values between 8-9 log10 Colony Forming Unit (CFU)/g in cheeses at 90 days of ripening. The four pathogenic bacteria were found in experimental curd at levels higher than those inoculated in milk and completely disappeared after 60 days of ripening. The RAPD analysis clearly demonstrated the presence of the added strain during production and confirmed the results of plate counts. Conclusion: This work showed that the production conditions of PDO Pecorino Siciliano cheese decreased growth of E. coli O157, L. monocytogenes, S. Enteritidis, and S. aureus.