Comparison of agar screen and duplex-PCR in determination of methicillin resistant Staphylococcus aureus (MRSA) strains isolated from nose of personnel in Hajar hospital of Shahre-kord, 2007

Methicillin resistant staphylococcus aureus strains are the most important agents of nosocomial infections. The conventional antibiotic susceptibility methods such as disk diffusion are not suitable for detection of these strains due to their heteroresistancy. Therefore, in this study, agar screen and duplex-PCR were compared in determination of methicillin resistant Staphylococcus aureus (MRSA) strains isolated from nose of personnel in Hajar hospital of Shahre-kord, 2007. In this experimental study a total of 204 nasal swabs from personnel of Hajar hospital over a period of 6 months were collected. The specimens were cultured on mannitol salt agar for primary isolation and identification of Staphylococcus aureus strains and their susceptibility pattern to oxacillin was assessed using agar screen method. Finally, using duplex PCR, the isolates were tested for the presence of mecA gene. Results were compared and sensitivity and specificity of the method was determined. In this study, 23 of the 52 (44%) Staphylococcus aureus isolates were resistant to oxacillin using agar screen method. However, mecA gene was detected in 27 of the 52 strains (52%). Our results showed that the sensitivity and specificity of agar screen method in determination of MRSA strains were 81.5% and 96%, respectively comparing with PCR. Oxacillin agar screen, comparing PCR, is an inexpensive, applied and phenotypical method with low false positive and suitable for screening of MRSA. However, due to its relatively high false negative results is not appropriate for screening of MRSA strains isolated from hospital-employed nasal carriers.