Influenza delle diverse condizioni colturali sullo sviluppo e tossinogenesi di Staphylococcus aureus.

Staphylococcus aureus is a major cause of foodborne diseases in many Countries. S. aureus can multiply readily in many foods and dairy products are probably the most frequently involved. Staphylococcal food poisoning is caused by the ingestion of enterotoxins produced in foods by some strains of S. aureus. Enterotoxins are generally produced in the late exponential or stationary phase of growth. This investigation was undertaken to determine how the production of enterotoxin of S. aureus is affected when staphylococci are grown in milk and in different pH and temperature conditions and in fresh cheeses. Growth and enterotoxin production were studied in milk at different pH (4.5, 5.0, 6.0 and 6.7) and different temperature conditions (10, 25 and 37 deg C). In unfavourable conditions the enterotoxin is detectable only with very high levels of staphylococcal contamination. Fresh cheese was artificially contaminated with S. aureus and it was demonstrated that the acid pH of this matrix acts positively both on bacterial growth and on enterotoxin production also when time-temperature conditions are favourable for a massive development. Our data confirm that the presence of a rich lactic microflora combined to a low level of pH and temperature can effectively limit the growth and above all the enterotoxin production of S. aureus