Initial antimicrobial treatment for bacteraemia is often based on the results of the gram stain from a positive blood culture, with confirmatory culture results and susceptibilities available within 24-48 hours. Empirical treatment with glycopeptides is common, resulting in undesirable selection pressures for the development and spread of vancomycin resistance as well as colonisation or infection by organisms such as vancomycin-resistant Enterococci. Although vancomycin is indicated for methicillin-resistant S. aureus (MRSA) bacteraemia, it is less effective for methicillin-susceptible S. aureus (MSSA) bacteraemia than β-lactam antibiotics but the latter are often only commenced once methicillin-susceptible status is known. Therefore, the rapid identification of MSSA/MRSA bacteraemia not only allows clinicians to switch to a more appropriate and effective treatment regime earlier, but also potentially decreases in-hospital transmission of MRSA by expediting initiation of appropriate infection control measures.
The challenge is to provide this information in real-time as blood cultures signal positive rather than as a batched process. Many molecular methods developed for this purpose are unable to be performed out of routine working hours due to costs and processing time required. The BD MAX™ provides a simplified molecular platform with minimal hands on time that would technically allow processing of positive blood cultures as they signal.
We assessed the application of using the BD MAX™ Staph SR kit with 200 consecutive positive blood cultures, which demonstrated gram positive cocci resembling staphylococci on gram stain, to rapidly identify MRSA and MSSA, and compared these results to culture.
Initial results indicate that 12.5% of the clinical blood cultures tested using the BD MAX™ Staph SR were positive for MRSA, with a further 8.3% identified as MSSA. The remaining 79.2% were negative for all targets (except the SPC target). No discrepant results were noted when compared to culture. Less than 5 min hands on time was required to achieve results (obtained within 2 h) and the process is easily incorporated into blood culture processing.