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.