Production of staphylococcal enterotoxins A, B, and C under conditions of controlled pH and aeration.

The production of enterotoxins A, B, and C by nine strains of Staphylococcus aureus has been studied under controlled conditions in a fermenter. The strain to strain differences between staphylococci producing a specific enterotoxin were very marked. Increasing aeration in shake flasks improved both growth and production of all extracellular proteins measured other than that of enterotoxin C, the yield of which was decreased in one strain at high aeration. Silicone antifoam decreased the production of extracellular proteins, although enterotoxin A production from three strains was much less affected than that of enterotoxins B and C. In a detailed study of three strains, production of enterotoxins A and C was considerably greater in a defined amino acid medium than in a casein hydrolysate medium and was optimal for all three enterotoxins between pH 6.5 and 7.3. Changes in the pH or medium used in the fermenter that led to increased enterotoxin production could generally be correlated with a change in growth pattern, showing an extended transition period from exponential to stationary phase. Three out of five enterotoxin-A producing strains produced significantly more enterotoxin at a controlled pH of 6.5 in the fermenter than in shake-flask cultures. The yields with strain 100 were about five times greater than hitherto reported. Since many foods are buffered at pH 6 to 6.5, some strains may, therefore, produce sufficient enterotoxin A to cause food poisoning, although little or none may be produced when grown under normal testing procedures.