Enumeration of sublethally heated staphylococci in some dried foods

Abstract

The effect of 45 substances to restore the salt tolerance of sublethally heat-injured Staphylococcus aureus was tested. Sodium pyruvate, yeast extract, L-histidine, casitone (Difco), ATP and acetyl phosphate were effective. For enumeration a repair medium was first used containing sodium pyruvate and penicillin in 1% skim milk. This step was followed by counting on Baird-Parker agar with penicillinase. This method was selective; fewer than 100 staphylococci/g food could be enumerated and it gave counts about 8 times higher than the method of Giolitti and Cantoni, used as a five-tube most probable number technique. Heat injury sensitized S. aureus to polymyxin.