Value of Xpert MRSA/SA blood culture assay on the Gene Xpert® Dx System for rapid detection of Staphylococcus aureus and coagulase-negative staphylococci in patients with staphylococcal bacteremia

Abstract The Xpert MRSA/SA BC assay was examined prospectively in patients with staphylococcal bacteremia including 6 patients with blood culture bottles inoculated with biological fluid (synovial fluid in 4 cases and peritoneal fluid in 2 cases). Among the 56 Staphylococci species isolated, 80.3% were coagulase-negative staphylococci (CoNS) and 19.7% were S . aureus . Methicillin susceptibility test results showed that 77.8% of isolates were methicillin-resistant CoNS (MRCoNS) and 22.2% of isolates were methicillin-susceptible CoNS (MSCoNS). Of 11 S . aureus isolates, 63.7% were methicillin-susceptible S . aureus (MSSA) and 36.3% were methicillin-resistant S . aureus (MRSA). Xpert MRSA/SA BC results showed that genotypic results were in concordance with phenotypic results in 94.6% of cases versus 5.4% of discordant cases. Of these 3 discordant cases, 1 S . aureus isolate had an MRSA phenotype and an SPA + mec + SCCmec − genotype and another S . aureus isolate was phenotypically MSSA and genotypically SPA + mec + SCCmec − , and 1 S . epidermidis isolate was phenotypically MSCoNS and genotypically SPA − mec + SCCmec − .