Evaluation of the BD Phoenix system for detection of methicilin resistance in Staphylococcus aureus isolates in comparison to BD GeneOhm MRSA assay.

Background: In order to identify methicillin-resistant Staphylococcus aureus isolates quickly, automated and semiautomated systems, commercial media, and identification kits are widely used. The Phoenix system (BD, Sparks, MD, USA) has been available since 2004 in our laboratory. This study evaluated the reliability of the Phoenix system for the detection of methicillin resistance in Staphylococcus aureus isolates in comparison to BD GeneOhm MRSA assay (Becton Dickinson Diagnostics GeneOhm, CA, USA).

Methods: A total of 206 clinically significant Staphylococcus aureus isolates, submitted to the clinical microbiology laboratory between March 2011 and May 2013, were included in the study. Phoenix panels were studied for identification and susceptibility testing according to manufacturers' instructions. The detection of MRSA was performed using the BD GeneOhm MRSA assay (Becton Dickinson Diagnostics GeneOhm, CA, USA). The assay is a qualitative real-time PCR method.

Results: The Phoenix system results and mecA gene pozitivity were concordant for 134 methicillin-resistant and 71 methicillin-susceptible strains. One discordant isolate, identified as mecA negative by the PCR method, was methicillin-resistant Staphylococcus aureus positive by the Phoenix system (oxacilline MIC = 2 microg/mL; cefoxitin MIC = 8 microg/mL). In this study, Phoenix automated system's sensitivity, specificity, negative predictive value, and positive predictive value are found as 100%, 100%, 100%, and 100%, respectively.

Conclusions: As a result of our study, use of the Phoenix automated identification method for the detection of methicillin-resistant Staphylococcus aureus isolates is a practical and reliable approach for daily clinical laboratory procedures.