Behavior of Staphylococcus aureus in the Presence of Bacteriocin Producer Enterococcus faecalis in Fresh Soft Cheeses

Introduction: Staphylococcus aureus is a pathogen of major concern in foods, especially milk and cheese, due to the production of thermoresistant enterotoxins. Dairy autochthonous microbiota is mainly composed of lactic acid bacteria (LAB) with recognized antagonistic potential over certain pathogenic and spoilage bacteria. Despite this, the impact of bacteriocin-producing LAB over S. aureus physiology and virulence in foods is still poorly understood.

Purpose: This study aimed at monitoring S. aureus behavior in the presence of bacteriocin-producing E. faecalis during the production of a fresh soft cheese.

Methods: S. aureus ATCC 29213 was inoculated (10³ CFU/ml) alone or in combination with E. faecalis 41FL1 (10⁶ CFU/ml) in 3L of microfiltered milk, yielding 5 cheeses of approximately 60 g each. The kinetics of bacterial growth, bacteriocin and staphylococcal enterotoxin production was monitored during 21 days.

Results: pH values in cheeses inoculated with E. faecalis reached 5.0 from day 0, whereas in cheeses with S. aureus alone pH decrease was observed only at day 7. Kinetics of E. faecalis growth and bacteriocin production was not altered in the presence of S. aureus. In contrast, S. aureus population in mixed culture showed a 3-fold decrease when compared to single culture, accompanied by lack of enterotoxin production. These data suggest a remarkable impairment of S. aureus virulence in the presence of bacteriocin-producing E. faecalis in cheese-mimicking conditions.

Significance: An improved understanding on how S. aureus cope with the presence of LAB in cheese can contribute to the development of new prevention strategies against this major foodborne pathogen.