Comparison of tests designed to identify Staphylococcus aureus thermostable nuclease

The thermonuclease test has been employed for same-day identification of Staphylococcus aureus in blood cultures and a seroinhibition test to confirm S. aureus thermonuclease (TNase) by using polyclonal anti-S. aureus TNase antiserum. However, strains of non-S. aureus staphylococci may produce TNases which are neutralized by the antiserum. This study evaluated alternative reagents and confirmatory tests for the S. aureus TNase. The tests included seroinhibition by a monoclonal antibody (MAb) against S. aureus TNase, MAb-based detection of the TNase in a sandwich ELISA, and a polymerase chain reaction for amplification of the nuc gene encoding the S. aureus TNase. All these tests discriminated between TNase produced by S. aureus and TNase produced by strains of the species S. caprae, S. carnosus, S. simulans, S. capitis, and S. intermedius. Specificity for the S. aureus TNase was confirmed by an inhibition ELISA for two out of three MAbs tested. Thus, the MAb- and nuc-based tests will be useful to discriminate between TNases from S. aureus and non-S. aureus staphylococci.