Comparison of Agar screen and duplex-PCR methods in determination of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from nasal carriage

Abstract

Methicillin-resistant Staphylococcus aureus strains (MRSA) have become a serious health issue in engendering nosocomial infections. Due to the heterogeneity of this type of resistance, the conventional antibiotic susceptibility tests may fail to detect MRSA strains. The purpose of this research was to compare the phenotypic agar screen method with polymerase chain reaction (PCR) for detection of MRSA strains isolated from the nasal samples of hospital personnel. Totally, 52 coagulase positive S. aureus strains were isolated from nasal samples of 204 hospital personnel of Hajar Hospital affiliated to Shahrekord University of Medical Sciences. Susceptibility to oxacillin in the strains was evaluated by the phenotypic agar screen method. The presence of the methicillin resistance gene, mec A, was studied through duplex PCR method. The results of both methods were compared and the sensitivity and specificity of the methods were determined. Totally, 23 out of the 52 isolated S. aureus (44%) were phenotypically resistant to oxacillin, but 27 (52%) carried mecA gene. The sensitivity and specificity of the phenotypic agar screen method for determination of MRSA strains were found to be 81.5 and 96%, respectively. As compared to duplex PCR, oxacillin agar screen method is a simple, inexpensive, and practical phenotypic method with relatively low false positive results and thus may be suitable for verification of suspicious MRSA strains. However, for the relatively high false negative results, it may not be recommended for the primary screening of MRSA strains from the nasal samples of healthy carriers working at hospitals. Key words: Nosocomial infections, methicillin resistance Staphylococcus aureus(MRSA), polymerase chain reaction (PCR)