Staphylococcus aureus and Enterotoxin A in Cream and Butter

Abstract

Cream was a satisfactory growth medium for Staphylococcus aureus at 37C but supported only minimal growth at 23C for 16 hr. After 24 hr at 37C,>1μg enterotoxin A per 100g cream was detected. When butter initially contained 105 to 106 staphylococci per gram, some growth occurred with 1% or less salt at 23C. Growth was not evident in butter with 1.5% salt but staphylococci remained stable at 23C for 14 days. However, this environment was detrimental to the organism during incubation at 10C for 60 days. Whipping of butter had little effect on staphylococcal behavior over that in unwhipped butter stored at 23C. At 10C, the number of viable staphylococci in whipped butter remained nearly constant or increased slightly during 60 days of storage. In unwhipped butter, viable staphylococci markedly declined so that up to a 400-fold difference in numbers existed between the two products after 60 days. When cream inoculated with S. aureus was incubated and churned, enterotoxin A appeared in the butter. The ratio of toxin in buttermilk: butter was approximately 8 to 16:l.