Effects of heat and pH stresses on the recovery of Staphylococcus aureus on medium-110.

The effects of heat and pH stresses on Staphylococcus aureus strain ATCC 10390 (coagulase positive) and strain ATCC 6020 (coagulase negative) were studied. The coagulase negative strain was more sensitive to heat and low or high pH than the coagulase positive strain. Both strains, however, were injured by heat and by pH 4.5 and 9 as estimated by the decrease in their tolerance to the selective agents (sodium chloride and sodium azide) present in the selective medium. The heat or pH injured cells, however, regained their tolerance to the selective agents if they were pregrown in a non-selective medium before they were plated on the selective medium.