Reassessment of the coagulase and thermostable nuclease tests as means of identifying Staphylococcus aureus.

A total of 91 enterotoxigenic strains of Staphylococcus auerus isolated from foods and tested for production of coagulase and thermostable nuclease and the ability to ferment glucose and mannitol showed, with the exception of four strains, a complete correlation among these properties. A similar correlation was observed with 103 cultures of S. aureus isolated from clinical material. In all instances, the coagulase reactions were sufficiently strong to be scored at either the 3+ or 4+ levels. Presumptive staphylococcal cultures isolated during routine examination of foods and yielding 2+ coagulase reactions or lower were invariably negative for thermostable nuclease production. It is suggested that the thermostable nuclease test be performed on cultures with doubtful coagulase reactions before classifying them as S. aureus.