Optimizing Detection of MEC-Mediated Methicillin Resistance in Coagulase Negative Staphylococcus Species

Abstract Introduction/Objective Parenteral therapy for invasive staphylococcal infections often comprises lipo/glycopeptides methicillin resistant (MR) organisms, with extended spectrum penicillins reserved those confirmed as susceptible (MS). While phenotypic antimicrobial susceptibility testing (AST) using cefoxitin has high accuracy differentiating MR/MS S. aureus, the same, simple approach does not reliably distinguish resistance among all coagulase negative Staphylococcus species (CoNS). As such, clinicians may work under an assumption that MS CoNS cannot be predicted by laboratories, leading to lipo/glycopeptide therapeutic use caused both MR and isolates. To better inform laboratory practice, this study aimed establish of multiple genotypic tests differentiation commonly recovered producing infections. Methods/Case Report A convenience sample 155 unique isolates historic Vitek 2 and/or disc diffusion (DD) AST results (~50% MR) were retrieved from frozen storage tested by: (1) oxacillin DD, (2) a lateral flow immunoassay PBP2a without beta-lactam induction, (3) lab-developed PCR mecA. commercial real-time mecA/C was also employed subset Results (if Case Study enter NA) total 144 belonging 11 taxa evaluated after accounting missing, non-viable, incorrectly cataloged Using detection reference standard, categorical agreement status 95.5% (127/133) original GP75 results, 98.6% (142/144) DD interpreted updated, species-specific CLSI guidelines, 100% (144/144) assay. Six five different repeatedly mecA-negative mecA/C-positive Conclusion Although methods sufficient accuracy, definitive determination is best achieved off-label/lab-developed mec or PBP2a.