EFFECT OF SODIUM CHLORIDE CONCENTRATION IN AN AGAR MEDIUM ON GROWTH OF HEAT-SHOCKED STAPHYLOCOCCUS AUREUS.

The numbers of Staphylococcus aureus 196E surviving heat treatment in milk for various times at 60 C were determined by plate count with normal and modified Staphylococcus Medium No. 110 (S-110), with Plate Count Agar (PCA), and by milk enrichment techniques. Portions of specific heated samples appeared to contain lower populations of S. aureus 196E when the survivors were enumerated with normal S-110 than with PCA. Similarly, the times at 60 C needed for total destruction of the culture suspension in the test milk appeared to be shorter when survival was determined with normal S-110 agar. The apparently lower thermal death times were found to be related to the NaCl content of the S-110 medium, because use of S-110 agar containing lesser concentrations of NaCl resulted in growth of larger numbers of heat-shocked S. aureus 196E.