Authors: Khawaja A , Arshad F , Asif M , Ahmad S , Yunus N , Hameed A

Abstract

Background and Objective: The versatility of Staphylococcus aureus has been transformed as “Methicillin resistant Staphylococcus aureus”. Among phenotypic methods for detection of MRSA, feasible technique, i.e., cefoxitin disc diffusion test and/or oxacillin disc diffusion test can significantly contribute to-wards reliable detection. The objective of the study is to determine methicillin resistance in Staphylococcus aureus by disc diffusion methods; and to evaluate their accuracy with mecA gene PCR for MRSA detection.
Methods: A total of 750 staphylococcus aureus isolates were screened with oxacillin disk (1 g) and cefoxitin disk (30 g) by Kirby-Bauer method using CLSI guideline (2016); to get 105 continuous, nonrepetitive clinical isolates of MRSA. All the methicillin resistant staphylococcus aureus isolates were further amplified by polymerase chain reaction for mecA gene detection.
Results: All the 105 MRSA isolates were resistant by both oxacillin and cefoxitin disk diffusion tests. On PCR amplification, out of 105 MRSA (oxacillin resistant) isolates, 83 (79.04%) isolates were positive for mecA gene. Among 105 MRSA (cefoxitin resistant) isolates, 89 (84.76%) were mecA gene positive, by PCR amplification. The sensitivity (96.73%) and diagnostic accuracy (94.28%) of cefoxitin disc diffusion method was higher than oxacillin disc diffusion technique, with reference to PCR as a gold standard.
Conclusion: Cefoxitin disc diffusion method can be employed reliably for detection of mecA gene in MR-SA isolates in settings with limited resources, where molecular methods are not available. This can efficiently reduce the misdiagnosis and dissemination of resistant strains.

Keywords: Methicillin resistant Staphylococcus aureus, Oxacillin, Cefoxitin, PCR.