Thermonuclease test for same-day identification of Staphylococcus aureus in blood cultures

We used a thermonuclease test to presumptively identify Staphylococcus aureus directly in blood cultures on the same day that a smear of the broth showed gram-positive cocci in clusters. There were no discrepancies between the identification of S. aureus directly from 250 blood cultures and identification by the tube coagulase test which was performed on the 18- to 24-h subculture isolates. These rapid results were clinically relevant and enabled physicians to make more timely and cost-effective decisions about antibiotic therapy.