Comparison of mecA Gene Detection with Susceptibility Testing Methods in Coagulase Negative Staphylococcus According to the New NCCLS Guidelines(1999)

Nam, Myung Hyun; Woo, Hee Yeon; Lee, Jang Ho; Lee, Nam Yong

Abstract

BACKGROUND
Coagulase negative staphylococcus (CNS) spp. is a major pathogenic organism of nosocomial and community-acquired urianry tract infections, and causes infrctions in the immunocompromised host, and in particular, bloodstream infetions in patent with indwelling devices. High prevalance of methicillin resistance has been noticed in CNS which also have been recongnized as an important multidrug resistant pathogen. The optimal phenotypic method for detecting methicillin resistance still remains controversial, and new guidelines for detecting methicillin resistance of CNS was proposed by NCCLS in January 1999. We evaluated the relationship between mecA gene by PCR method and antimicrobial susceptibility tests according to the new NCCLS guidelines.
METHODS
A total of 82 CNS isolates were examined for MICs and penicillin MICs by disk diffusion and agar dilution method according to NCCLS guidelines, and detections, and detection of mecA gene by PCR. RESULT: In disk diffusion method, 66 strains (80.5%) and 63 strains (76.8%) showed resistance to penicillin and oxacillin, respectively, and in agar dilution method, 71 strains(86.6%) and 53 strains (64.6%), respectively. In PCR method, mecA genes were detected in 49 strains(59.8%). Comparing with mecA gene detection by PCR method, the sensitivity of disk diffusion and agar dilution method was 95.8% and 89.8%, repectively. However, the sensitivity of disk diffusion and agar dilution method was 65.3% and 75.5%, respectively using previous NCCLS criteria.
CONCLUSION
The new criteria of NCCLS detects the methicillin resistance induced by mecA gene more sensitively than previous one.