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

Abstract

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 18to 24-h subculture isolates. These rapid results were clinically relevant and enabled physicians to make more timely and cost-effective decisions about antibiotic therapy.

Species-Specific and Ubiquitous-DNA-Based Assays for Rapid Identification ofStaphylococcus aureus

“…These methods include coagulase tests (9), a panel of commercial agglutination tests (7,13,34), a hybridization test for rRNA (8), and an enzymatic test for the detection of thermostable nuclease (18,23). Although identification with the thermonuclease enzyme test has shown an excellent correlation with the conventional identification of S. aureus isolates (18,23), false-positive results due to thermonuclease activity in some strains of coagulase-negative staphylococci may occur (6,10,17). In addition, some streptococcal isolates may give a positive thermonuclease test (20).…”

Comparison of tests designed to identify Staphylococcus aureus thermostable nuclease

“…Previously, we have tested additional non-S. aureus isolates, some of which were also positive in the thermonuclease test (4,5,9). Although the thermonuclease test has been used to identify S. aureus isolates from human and veterinary clinical specimens, including same-day identification of blood culture isolates (21,24), environmental or dietary product isolates (14, 23), our results substantiate the lack of specificity of this test for S. aureus. Furthermore, the seroinhibition test based on polyclonal anti-TNase serum failed to confirm the species S. aureus, since this antiserum also inhibited the activity of non-S. aureus TNases to a considerable extent.…”

“…The thermonuclease test for DNA degradation by the thermostable nuclease (TNase) produced by S. aureus, originally described by Lachica et al (19), is regarded as reliable for identification of this bacterium by direct examination of blood cultures (21,24). However, strains of the species S. schleiferi, S. carnosus, S. intermedius, S. hyicus, S. caprae, and S, capitis may produce TNases (10,17,18).…”

Update on detection of bacteremia and fungemia.

“…The susceptibility of S. aureus to lysostaphin was reported to be an excellent way to distinguish this organism from CNS (157,158). Subsequently, testing with thermonuclease, a heat-stable DNase produced by S. aureus, was reported to be a rapid, accurate identification method (102,137). The test could be performed from either standard blood culture broths or BACTEC bottles with a positive growth index (144).…”