An evaluation of the advandx Staphylococcus aureus/CNS PNA FISH assay

A study was conducted to compare the S. aureus/CNS PNA FISH Culture Identification Kit (AdvanDx, Woburn MA) to standard microbiology identification methods for presumptive identification of S. aureus and coagulase-negative staphylococcus (CNS) in positive blood cultures.

Blood cultures (n=301) that signaled positive on the BacT/Alert 3D (bioMerieux, Durham NC) automated blood culture system and had gram-positive cocci in clusters on Gram stain were processed using standard microbiology methods and were analyzed with the S. aureus/CNS PNA FISH assay. The S. aureus/CNS PNA FISH assay was performed in accordance with the manufacturer's instructions.

Overall agreement was 96.7%. Sensitivity for S. aureus was 96.5% (83/86). Specificity for S. aureus was 100% (215/215). Sensitivity for CNS was 96.6% (201/208). Specificity for CNS was 96.8% (90/93). Three cultures reported as S. aureus were identified as CNS by S. aureus/CNS PNA FISH. Three cultures that reported only S. aureus were positive for both S. aureus and CNS by S. aureus/CNS PNA FISH. One S. viridans was identified as CNS by S. aureus/CNS PNA FISH. Seven cultures that reported CNS were negative by S. aureus/CNS PNA FISH.

When used in conjunction with Gram stain and culture the S. aureus/CNS PNA FISH assay may be beneficial in terms of reducing time to correct therapy, thereby decreasing mortality and costs associated with S. aureus bacteremia.