Effect of growth of a commercial starter culture on growth of Staphylococcus aureus and thermonuclease and enterotoxins (C1 and C2) production in broth cultures.

Staphylococcus aureus strains FRI 137 (enterotoxin C1 producer) and FRI 361 and L 2 (enterotoxin C2 producers) were grown alone and in the presence of a mixed commercial starter culture (Streptococcus lactis, Streptococcus cremoris and Streptococcus lactis subsp. diacetylactis). Lactic acid bacteria had a slight inhibitory effect on S. aureus population and only during the late stages of growth. In contrast, enterotoxin synthesis was strongly inhibited, inhibition at 18 h being 89% (FRI 137), 80% (FRI 361) and 69% (L 2). Enterotoxin C1 was produced and accumulated during all phases of growth in pure and mixed culture, but associative growth resulted in reduction of enterotoxin C2 after 24-36 h. In mixed culture, high producers of thermonuclease (FRI 137 and L 2) showed an early decrease in enzyme activity followed by an increase, but it never reached levels attained in pure culture. Thermonuclease was detected whenever enterotoxin was detected, but production curves did not parallel each other.