Comparison of Different Phenotypic Methods of Detection of Methicillin-Resistant Staphylococcus aureus with Polymerase Chain Reaction

Objectives: The objective of the current study was to compare the diagnostic methods of Oxacillin Disk Diffusion, Cefoxitin Disk Diffusion, Oxacillin Resistance Screening Agar Base, and CHROM Agar MRSA with the gold-standard method of Polymerase Chain Reaction for detection of Methicillin-resistant Staphylococcus aureus. Methods: Two hundred pus samples were included in the study from which Staphylococcus strains were evaluated. The isolates of Staphylococcus aureus were subjected to the Oxacillin Disk Diffusion test, Cefoxitin Disk Diffusion test, Oxacillin Resistance Screening Agar Base, and CHROM Agar MRSA to detect MRSA with PCR, the reference standard. The diagnostic techniques were compared to their sensitivity, specificity, positive predictive, and negative predictive values. Results: The sensitivity of the Cefoxitin Disk Diffusion test was 100%, followed by CHROM Agar MRSA at 96.7%, Oxacillin Disk Diffusion at 90%, and Oxacillin Resistance Screening Agar Base at 86.7%. Most specific was the Cefoxitin Disk Diffusion test (99.4%), followed by Oxacillin Resistance Screening Agar Base (98.8%), CHROM Agar MRSA (97.7%), and the least specific was the Oxacillin Disk Diffusion test (96.5%). Conclusion: The Cefoxitin Disk Diffusion test was the most sensitive and specific of all four methods, next to the Polymerase Chain Reaction. However, future multicentric studies are recommended to test this method across all prevalent centers of methicillin resistance. J Microbiol Infect Dis 2022; 12(3):116-126.