Lactic acid bacteria as biocontrol agents to reduce Staphylococcus aureus growth, enterotoxin production and virulence gene expression

The capacity of six lactic acid bacteria (LAB) strains to decrease both the growth of Staphylococcus aureus UCLM-1 and the production of staphylococcal enterotoxins growing in co-culture in sheep's milk, was evaluated. During incubation of the cultures, samples were taken to monitor LABs and Staphylococcus growth, pH, production of organic acids, presence of the staphylococcal enterotoxins A, B, C, D, and E and the expression of 11 staphylococcal genes involved in virulence and enterotoxin production. Strains Lactiplantibacillus plantarum UCLM-101 and UCLM-56 yielded the highest decreases of both Staphylococcus aureus viable cell counts and pH, followed by the strain Levilactobacillus brevis UCLM-99. Analysis of organic acids and enterotoxins production by these three strains displayed that the main acid produced was lactic acid, while enterotoxins were not detected in the co-cultures with any of them. In addition, a decrease in the expression of some staphylococcal genes was observed, which varied depending on the LAB strain and the incubation time. Results allow us to propose the use of any of these three strains as biocontrol agents in the manufacture of “free of preservatives” dairy products, to avoid the risk of staphylococcal foodborne infections.