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Staphylococcus aureus growth and enterotoxin production in co-culture with Lactococcus garvieae were studied in laboratory medium as a function of incubation temperature and pH values. Doehlert experimental design was used to study the effect of L. garvieae concentration, temperature, and pH on S. aureus growth in laboratory medium. The mathematical model obtained was validated in cheeses. The inhibition of S. aureus growth by L. garvieae was more important during the first 6 hours of incubation, and its effect increased when its concentration increased. After 24 and 48 hours, the effect of L. garvieae decreased, and the growth of S. aureus was positively influenced by higher temperature and pH values. Staphylococcal enterotoxins were detected in only one experimental set after 48 hours of incubation at 30 degrees C at pH 6.8. Our results argue in favor of adding antagonist strain early in the cheese-making process.

Staphylococcus aureus growth and enterotoxin production during the manufacture of model Saint-Nectaire, Registered Designation of Origin Saint-Nectaire, and Registered Designation of Origin Salers cheeses, three types of uncooked, semihard, raw milk cheese, were investigated. Coagulase-positive staphylococci (SC+) grew rapidly during the first 6 h. Between 6 and 24 h, counts increased by less than 0.5 log CFU/ml. Raw milk counts ranged from undetectable (<10 CFU/ml) to 3.03 log CFU/ml. Maximal levels reached in cheese on day 1 ranged from 2.82 to 6.84 log CFU/g. The level of SC+ after 24 h was mainly influenced by the milk baseline SC+ level (correlation coefficient, r > 0.80) but pH at 6 h influenced the SC+ growth observed between 6 and 24 h (r > 0.70). Thus, the initial level of SC+ in raw milk should be maintained below 100 CFU/ml and best below 40 CFU/ml. To limit growth, acidification should be managed to obtain pH values around or below 5.8 at 6 h in Saint-Nectaire cheeses and around or below 6.3 at 6 h in Salers cheeses. Enterotoxins were only detected in two Salers cheeses whose SC+ counts on day 1 were 5.55 log CFU/g and 5.06 log CFU/g, respectively, and whose pH values at 6 h were high (approximately 6.6 and 6.5, respectively).