Potential Misidentification of Methicillin Resistant S. Aureus based on Nuc- Specific PCR.

Abstract

PCR based on amplification of nuc gene (encoding staphylococcal thermostable nuclease) is considered as a reliable method for identification of MRSA strains. The aim of this study was to evaluate the efficiency of nuc-specific PCR as the sole molecular method for identification of MRSA. Sixty MRSA strains isolated from clinical samples from outpatients were identified phenotypically and subject to PCR for detecting mecA and 16S rRNA genes. Then, all isolates were subjected to PCR to detect two different regions of nuc gene (270 bp and 430 bp). Resistance to methicillin was investigated by cefoxitin disk diffusion test. The results showed that all tested strains were resistant to cefoxitin and positive for mecA and 16S rRNA genes. Out of 60 isolates, 58 strains exhibited amplification of 423bp and 55 strains showed amplification of 270 bp product of nuc gene. The five strains (8.3%) which failed to amplify 270bp were positive for 423bp product of nuc gene and the two strains (3.3%) which failed to amplify 423bp were positive for 270bp region. The discrepancies between the results indicated that the nuc-specific PCR method is not sufficient alone. Therefore, combination of other species-specific target would be useful to avoid potential false negative results.