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Growth and Production of Enterotoxin A by Staphylococcus aureus in Cream

Department of Food Science and The Food Research Institute, University of Wisconsin-Madison, Madison 53706

ABSTRACT

Behavior of Staphylococcus aureus strains 100-A, 196-E, 254, 473, 505, and 521 in sweet (18 to 80% milk fat) and neutralized sour cream was studied. Cream was inoculated to contain approximately 10³ to 10⁴ S. aureus/ml, depending on milk fat content, and was incubated at 4, 22, or 37°C. Determinations were made of aerobic plate count, S. aureus count, and pH. When growth in cream exceeded 10⁷ S. aureus/ml, enterotoxin analysis was done. Sweet and neutralized sour cream supported growth of all strains of S. aureus tested. Strains 100-A, 196-E, 473, 505, and 521 grew sufficiently to produce enterotoxin in sweet cream of 18 or 32% milk fat held at 37°C for 18 h or at 22°C for 52 h. Populations of strains 100-A, 196-E, 505, and 521 exceeded 106 cells/ml in sweet cream of 36% milk fat held for 18 h at 37°C. Strains 100-A and 521 grew to more than 10⁶ cells/ml in sweet cream of 40% milk fat held for 18 h at 37°C. No strain of S. aureus grew to levels associated with detectable enterotoxin production at 4°C within 14 d in any cream. Incubation temperature, milk fat content of cream, and variation among strains influenced the ability of S. aureus to grow and produce enterotoxin.