Selective Enterotoxin Production in Foods by Staphylococcus aureus Strains That Produce More Than One Enterotoxin

Staphylococcus aureus strain S-6, producer of enterotoxins A and B; strain FRI-913, producer of enterotoxins A, C, and E; and strain FRI-196E, producer of enterotoxins A and D, were grown in milk (pH 6.8), potato salad with mayonnaise, and boiled egg white (pH 8.0-8.5). Enterotoxins were detectable in milk incubated at 26°C when colony counts were less than 10⁶. Enterotoxin production by strain S-6 was detectable in potato salad at 10⁶ CFU at both 26 and 37°C. Enterotoxin A production by strain FRI-913 was detectable at approximately 10⁶ CFU/g, whereas enterotoxin C was detectable only when growth reached approximately 10⁸ CFU/g. Production of enterotoxins A and D by strain FRI-196E was detectable when growth was greater than 10⁷ CFU/g. Production of enterotoxins A and B by strain S-6 in boiled egg white was detectable at greater than 10⁶ CFU/g. In most experiments, enterotoxins A and C from strain FRI-913 were detectable when cell counts were greater than 10⁷ CFU/g, whereas enterotoxin A and enterotoxin D production by strain FRI-196E was detectable at counts between 10⁵ and 10⁶ CFU/g. It can be concluded that enterotoxin production is influenced by the time of incubation and the composition and pH of the food.