A Study of the mecI, mecA and femA Genes of Methicillin-Resistant Staphylococci

Ahn, Jee Young; Kim, Won Bae; Lee, Dong Wha; Lee, Kyung Won; Choi, Seok Ho; Kim, Il Soo; Seo, Chae Hyung

Abstract

BACKGROUND
Staphylococcus aures and Staphylococcus epidermidis are those of the important pathogens that have revealed the increase of methicillin resistance. Because of increasing prevalence of staphylococci resistant to one or more antimicrobial agents, it is necessary to determine the antibiotic susceptibility of these microorganisms. Methicillin resistance is due to the production of PBP2', which is encoded by mecA gene in the chromosome. PBP 2' shows low affinity to the all of beta-lactam drugs. Therefore, the determination of gene is considered as a correct method for the antibiotic treatment procedures. METHOD: In order to examine effectiveness of detecting mecA and femA genes for the identification of methicillin resistant S. aureus (MRSA) and mecI gene in high-level-resistant MRSA, the presence of these genes in S. aureus and S. epidermidis was investigated by PCR. The types of genes were compared with phenotype by agar dilution method and investigated with MIC of methicillin.
RESULTS
1. The mecA gene detection was useful for the identification of MRSA with MRSA 100% and methicillin susceptable S. aureus (MSSA) 2.7% (P<0.001); and not useful for the identification of methicillin resistant S. epidermidis (MRSE) with MRSE 93.8% and methicillin susceptable S. epidermidis (MSSE) 52.9% (P>0.001). 2. The femA gene detection was useful for the S. aureus identification (P<0.001) and specificity 100% with MRSA 100% and MSSA 100%, MRSE and MSSE being 0%. 3. The mecI gene detection revealed MRSA 59.4%, and high-level-resistant MRSA was not detected in 39%. There was no validity of existence and nonexistence between the degree of methicillin MIC and the detection of mecI gene (P>0.001).
CONCLUSION
The study concluded that the detection of both the mecA and femA genes from staphylococci by the PCR method had been considered as a correct and useful method in the identification of MRSA. mecI gene has been deemed as a repressor gene for high-level-resistant MRSA that is clinically useful as a standard. However, it is considered that the investigation should be done with later detected nucleotide sequencing of the mecI gene.