Direct mecA polymerase chain reaction testing of blood culture bottles growing Gram-positive cocci and the clinical potential in optimizing antibiotic therapy for staphylococcal bacteremia

This study evaluated the performance of direct mecA polymerase chain reaction (PCR) from blood culture bottles growing Gram-positive cocci in clusters and its role in optimization of antibiotic therapy. A total of 266 blood cultures including 121 methicillin-resistant and 122 methicillin-susceptible Staphylococci were tested for mecA. Compared to phenotypic testing, the overall performance of direct mecA PCR was 99% for sensitivity, specificity, positive predictive value, and negative predictive value, respectively. Assessment of antibiotic therapy upon microbiology reporting of direct mecA PCR results from 38 patients prior to (phase I) and 48 patients after implementation of testing and reporting (phase II) showed that the mean time to antibiotic optimization in phase II (0.9 ± 0.9 day) was significantly shorter than that in phase I (2.2 ± 3.2 days) (P < 0.05). Methicillin-susceptible staphylococcal bacteremias had significantly higher frequency of antibiotic adjustment upon direct mecA reporting, compared to methicillin-resistant staphylococcal bacteremias. Our study indicated that direct mecA PCR improved timely antibiotic optimization.