Evaluating the performance of the Alere PBP2a SA Culture Colony Test with the Vitek 2 Antimicrobial Susceptibility Test Card System as reference standard in coagulase-negative Staphylococcus species

Background: The Alere PBP2a SA Culture Colony Test is an FDA-cleared in vitro immunochromatographic assay for rapid detection of penicillin-binding protein2a (PBP2a) in Staphylococcus aureus. . Methods: We investigated the performance of the PBP2a SA Culture Colony Test with 78 coagulase-negative Staphylococcus (CoNS) isolates from different body sites, with the Vitek 2 Antimicrobial Susceptibility Test (AST) as a reference standard. Results: The CoNS species were 62 S. epidermidis; ; 6 S. lugdenensis; ; 3 S. hominis; ; 2 S. capitis; ; 2 S. haemolyticus; ; and 1 each of S. simulans, S. auricularis, and S. warneri. . Of the 78 CoNS isolates, 68 showed concordance in the PBP2a IC assay and Vitek 2 AST. Discordance was seen for 10 S. epidermidis isolates, which showed negative in the PBP2a assay, despite oxacillin-resistance detection using the Vitek 2 AST (66.7% sensitivity and 100% specificity). All non- S. epidermidis CoNS were identified with 100% concordance using the PBP2a IC assay and Vitek 2 AST. Conclusion: We demonstrated that, while the PBP2a IC assay has low sensitivity in determining the susceptibility of S. epidermidis to oxacillin, it highly accurately predicted the susceptibility of non- S. epidermidis CoNS to oxacillin. The diagnostic accuracy for non- S. epidermidis CoNS needs further assessment with more isolates to confirm our findings.