Combined Effect of Water Activity, pH and Sub‐optimal Temperature on Growth and Enterotoxin Production of Staphylococcus aureus

Staphylococcus aureus growth and enterotoxin production in relation to a, (0.99–0.87), pH (4.0–7.0) and temperature (8–30°C) was determined in Brain‐heart‐infusion broth with respectively NaCl and sucrose as humectants. Growth of S. aureus was not observed at a w 0.85, at pH 4.3 or at 8°C. At 12°C no growth occurred at a, 0.90 or at a, 0.93 in combination with pH < 5.5. At a w 0.96 no growth occurred at pH ≤ 4.9. Production of staphylococcal enterotoxin type A (SEA) occurred under nearly all conditions allowing growth. Production of SEB appears to be determined by a w ; at a w 0.96 SEB was produced at all temperatures allowing growth, while at a, 0.93 SEB was hardly produced. Production of SEC and SEF was affected both by a w and temperaure. Production of these toxins was rarely observed at a, 0.93. No SEC and SEF were produced at 12°C. Extrapolation of these findings to food is discussed.