The enumeration of sublethally injured populations of Staphylococcus aureus in foods

Substantiating earlier investigations, pure cultures of Staphylococcus aureus were found to be equally well recovered on Baird‐Parker agar at 37°C as at 42°C, whereas Micrococcus spp. are suppressed at the latter temperature to an extent exceeding 5 log10 cycles. It was also established that egg yolk dissimilation by Staph. aureus is intensified at 42°C. Heat treated (60°C) populations of Staph aureus were quantitatively recovered on Baird‐Parker agar at 42°C, though acid‐injured populations were not. Acid‐injury (2% lactic acid at 37°C) could be completely restored by solid medium repaiar during at least 6 h at 23°C on tryptone soya peptone yeast extract egg yolk pyruvate agar. Pure culture studies were confirmed in surveys on trade samples of foods.