Staphylococcus aureus and Enterotoxin A in Cream and Butter

Cream was a satisfactory growth medium for Staphylococcus aureus at 37 C but supported enly minimal growth at 23 C for 16 hr. After 24 hr at 37 C, > 1 /~g enterotoxin A per 100 g cream was detected. When butter initially contained l0 s to 106 staphylococci per gram, some growth occurred with 1% or less salt at 23 C. Growth was not evident in butter with 1.5~o salt but staphylococci remained stable at 23 C for 14 days. However, this environment was detrimental to the organism during incubation at 10 C for 60 days. Whipping of butter had little effect on staphylococcal behavior over that in unwhipped butter stored at 23 C. At 10 C, the number of viable staphylococci in whipped butter remained nearly constant or increased slightly dmSng 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 16:1.