Growth and Production of Enterotoxins A and D by Staphylococcus aureus in Salad Bar Ingredients and Clam Chowder

Growth and production of enterotoxins A and D (SEA, SED) by two strains of Staphylococcus aureus were determined in salad bar ingredients and clam chowder. Salad bar ingredients included lettuce, canned black olives, canned green olives, tomato, green pepper, blue cheese salad dressing, blue cheese crumbles, celery, and croutons. Total S. aureus were determined by plate count on Baird-Parker agar. Enterotoxins were quantified by using an ELISA technique. S. aureus did not survive in salad dressing, with pH 4.3. With the exception of olives and blue cheese, S. aureus survived on all ingredients for more than 12 h. After 24 h, the total number of cells decreased on most of the ingredients. S. aureus grew well on green pepper during the first 24 h, reaching 10⁵ CFU/g, but no enterotoxins were detected. S. aureus also increased in moist and dry plain croutons, but there was no detectable production of enterotoxins. S. aureus growth was excellent in clam chowder with cell counts exceeding 10⁸ CFU/g after 12 h at 42°C. Production of SEA and SED began shortly after 3 h. Maximal levels of SEA and SED were 0.29 and 1.6 ng/g, respectively, after 12 h. In brain heart infusion broth, the production of SEA and SED reached 21.9 and 36.3 ng/ml, respectively, after 24 h at 37°C.