Combined effects of water activity and pH on growth and enterotoxin A, B and C production by Staphylococcus aureus

Abstract

Combined effects of pH (4.5-7.4) and water activity (a_w, 0.99-0.88) on the growth and enterotoxin production by five Staphylococcal strains 100, S-6, 361, K858 and T7436, producing enterotoxins A, B, C, AB, and AC, respectively, were studied in Brain Heart Infusion broth for 48hr. At 35C, Staphylococcal enterotoxin A (SEA) was produced at a_w>0.92 or at pH>4.5, but no SEA was produced at a_w 0.92 and pH 5.3. SEB and SEC were produced at a_w>0.96 and pH>5.3 and a_w>0.96 and pH>4.5, respectively. No SEB was produced at a_w 0.96 and pH 5.3. No growth occurred at a_w<0.92 and pH 4.5. The enterotoxin production changed depending on the interaction of these factors. SEA production was much less affected by a_w and pH than was SEB and SEC. The enterotoxin production by the strains K858 and T7436 producing respectively SEA plus SEB and SEA plus SEC were both affected.