Enzymatic detection of the growth of Staphylococcus aureus in foods.

A specific method has been developed for the extraction and measurement of staphylococcal nuclease in foods in which Staphylococcus aureus has grown. The method was used to compare staphylococcal growth with nuclease production in foods under varying conditions of temperature, aerobiosis, and competition from other microorganisms. It was concluded that the nuclease is produced under any conditions that permit growth of S. aureus, and little or no interference with the test was encountered either from mixed, natural populations or from a variety of pure, laboratory cultures. Nuclease and enterotoxin A production were shown to vary in synchrony for the 234 (Casman) strain of S. aureus, and the sensitivity of the enzymatic detection of nuclease was comparable to the sensitivity of serological detection of enterotoxin A. It was found that 15 min at 121 C was required to reduce the nuclease activity in slurries of contaminated ham below the level present in the unheated slurry. The extraordinary heat resistance of the nuclease permits its detection even in foods heated subsequent to the growth of S. aureus. The nuclease analysis requires about 3 hr to complete and requires no unusual equipment or reagents.