Rapid detection of methicillin resistant Staphylococcus aureus bacteremia using a combined three-hour short-Incubation-MALDI-ToF identification and the Alere culture colony PBP2a detection test.

Meticillin-resistant Staphylococcus aureus (MRSA) bloodstream infection is responsible for significant morbidity, with mortality rates as high as 60% if not treated appropriately. We describe a rapid method to detect MRSA in blood cultures using a combined three-hour short incubation BRUKER matrix-assisted laser desorption/ionization time-of-flight MS BioTyper protocol and a qualitative immunochromatographic assay, the Alere Culture Colony Test PBP2a detection test. We compared this combined method with a molecular method detecting the nuc and mecA genes currently performed in our laboratory. One hundred and seventeen S. aureus blood cultures were tested of which 35 were MRSA and 82 were meticillin-sensitive S. aureus (MSSA). The rapid combined test correctly identified 100% (82/82) of the MSSA and 85.7% (30/35) of the MRSA after 3 h. There were five false negative results where the isolates were correctly identified as S. aureus, but PBP2a was not detected by the Culture Colony Test. The combined method has a sensitivity of 87.5%, specificity of 100%, a positive predictive value of 100% and a negative predictive value of 94.3% with the prevalence of MRSA in our S. aureus blood cultures. The combined rapid method offers a significant benefit to early detection of MRSA in positive blood cultures.