Evaluation of accuracy of Phenotypic methods in the detection of Methicillin Resistant Staphylococcus aureus

Abstract: Methicillin resistant Staphylococcus aureus (MRSA) is a variant of Staphylococcus aureus; responsible for a significant share of the infectious load. Objective: The current study was conducted to evaluate the accuracy of already in vogue phenotypic methods of identification of MRSA keeping in view the gold standard method of mec-A gene detection using Polymerase chain reaction (PCR) and to compare the sensitivity and specificity of different phenotypic methods (Cefoxitin Disc Diffusion, Oxacillin Disc Diffusion, Oxacillin Screen Agar, and MIC of Oxacillin by Agar Dilution Method) with the genotypic method (PCR). Method: A descriptive cross-sectional study was carried out at Microbiology Lab, Pakistan Railway Hospital, Rawalpindi from October 2021 to September 2022, after attaining the formal approval from Institutional Ethical Review Committee (Riphah/IIMC/IRC/21/73), using non-probability sampling technique. A total of 222 samples of Staphylococcus aureus were isolated from all the clinical specimens received at Microbiology lab at Pakistan Railway Hospital. Among those isolates, 150(67.5%) were Methicillin sensitive Staphylococcus aureus (MSSA) and 72(32.4%) were Methicillin Resistant Staphylococcus aureus (MRSA). The results of Phenotypic methods were compared with the results of PCR by using Chi-square formula. The sensitivity and specificity of Cefoxitin Disc Diffusion method was 62.5% and 96.6%, Oxacillin Disc Diffusion method was 65.3% and 93.3%, Oxacillin Screen Agar technique was 81.9% and 96% while that of Oxacillin MIC by Agar Dilution was 91.6% and 89.3% respectively. Oxacillin screen agar demonstrates the better phenotypic technique for detection of MRSA in routine practice.