Detection of Methicillin-resistant Staphylococcus aureus Strains by Comparing Oxacillin and Cefoxitin Disk Diffusion methods and PCR for mecA Gene

Methicillin-resistant Staphylococcus aureus, MRSA strains can pose a serious threat as nosocomial infections in various communities. In detection of these strains, PCR is an expensive method, whereas disk diffusion can provide a simple, inexpensive method with a high specificity. This study attempted to evaluate the disk diffusion method using cefoxitin and oxacillin discs compared with the PCR for detecting mecA gene.

In this study, 150 Staphylococcus aureus isolates were collected from clinical skin samples from the patients and personnel in Qom. Next, methicillin resistance was diagnosed using oxacillin and cefoxitin disk diffusion method. Using PCR, mecA gene was identified in Staphylococcus aureus isolates and the data of both disk diffusion method and PCR were compared.

Among the 150 isolates, 33% were methicillin-resistant in oxacillin disk diffusion, while 28% were methicillin-resistant in cefoxitin disc diffusion. The results revealed that oxacillin disk diffusion yielded false resistance to methicillin by 14% in detection of MRSA strains as compared to cefoxitin disk diffusion.

In laboratories where molecular methods are not employed as a routine procedure for MRSA detection, cefoxitin disk diffusion can provide a simple, low-cost and promising alternative technique for detection of methicillin-resistant isolates. Keywords:MRSA, Cefoxitin, Oxacillin, mecA