Staphylococcus aureus, thermostable nuclease and staphylococcal enterotoxins in raw ewes' milk Manchego cheese

Growth and survival of two enterotoxigenic strains of Staphylococcus aureus were studied during manufacture and ripening of eight batches of raw ewes' milk Manchego cheese. Only 2–3 generations of Staph. aureus occurred in the vat and during pressing. The death rate of Staph. aureus (mean decrease in log cfu/g/week of ripening) from day 1 to day 60 was 0.421 in cheese made with 1% Streptococcus lactis starter and 0.404 in cheese made without starter. Thermostable nuclease was produced in the vat by growing Staph. aureus cells; it was inactivated by rennet during the first 24 h and synthesized again by surviving cells of Staph. aureus from day 1 to day 60. Staphylococcal enterotoxins A, B, C and D were not detected in any batches of cheese, even though Staph. aureus counts exceeded 10⁷ cfu/g.