Evaluation of real-time PCR assay for rapid detection of Methicillin-Resistant Staphylococcus aureus (MRSA) directly from positively flagged blood cultures

Authors: Bharathikumar Sivakumar, Deepika K A, Benedict Vinothini A, Meerabai Manoharan, Madhan Sugumar, Apurba Sastry

DOI: 10.18231/j.ijmr.13288.1761802869

Keywords: MRSA, BSI, real time PCR from broth, conventional PCR, agreement

Abstract: Background: Methicillin-resistant Staphylococcus aureus (MRSA) represents a leading cause of bloodstream infections (BSIs), often associated with increased morbidity, mortality, and prolonged hospital stays. Timely and accurate detection of MRSA is essential for initiating appropriate antimicrobial therapy and implementing infection control measures. Phenotypic methods are time-consuming and cause a delay in the treatment decision. Such drawbacks can be overcome by the rapid detection of MRSA by real-time PCR from blood culture broth directly. This study aimed to evaluate the concordance between detection of mecA gene directly from blood culture broth flagged-positive for Staphylococcus aureus using real-time PCR and from the colony using conventional PCR. Methods: A total of 100 positively flagged blood culture bottles identified as S. aureus by MALDI-TOF were subjected to real-time PCR to detect the mecA gene. After colony growth, conventional PCR was carried out on confirmed S. aureus colonies. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and kappa agreement were calculated to assess diagnostic performance of real time PCR from broth. Phenotypic data, oxacillin MIC and cefoxitin disc diffusion, were also collected to assess their concordance to real time PCR. Results: The sensitivity and specificity of real time PCR was 100% and 96.7% respectively. The total agreement of real time PCR from positively flagged blood culture broth to conventional PCR and cefoxitin disk diffusion was found to be 98%, and 95% for oxacillin microbroth dilution. Conclusion: Real-time PCR is a highly sensitive and efficient molecular diagnostic tool, for the direct detection of MRSA from blood culture broth. Alongside cefoxitin DD as the phenotypic method, discrepancies in real time PCR were significantly reduced.