[Detection of methicillin-resistant Staphylococcus aureus by in vitro enzymatic amplification of mecA and femA genes].

In the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection, rapid detection of MRSA is extremely important. The mecA gene codes the new drug resistant polypeptides called penicillin-binding protein 2a (PBP2a) or 2'(PBP2'), which mediates the clinically relevant resistance to all beta-lactam antibiotics. This gene could be beneficial in the detection of MRSA using the polymerase chain reaction (PCR). However, the identical mecA gene has been found in both coagulase-positive and coagulase-negative Staphylococcus with the appropriate methicillin-resistant phenotype. The second gene related to the expression of methicillin-resistance has been called femA. In this study, we amplified both mecA and femA genes by PCR in 97 strains and 32 clinical specimens. The mecA gene was positive in all 63(100%) MRSA strains and 2(6%) of the 34 methicillin-sensitive Staphylococcus aureus (MSSA) strains. Two strains with the methicillin-sensitive phenotype and the mecA gene resulted in methicillin-resistance when cultured on an agar plate containing 4.5% NaCl. The mecA gene was also present in all 10(100%) coagulase-negative Staphylococcus strains with the methicillin-resistant phenotype. The femA gene was positive in all 97(100%) MRSA and MSSA strains. On the other hand, the femA gene was absent from coagulase -negative Staphylococcus strains with the methicillin-resistant phenotype. Although the mechanism by which the product of femA gene influences the expression of methicillin-resistance is unknown, the gene appears to be restricted only in coagulase-positive Staphylococcus, regardless of methicillin-resistance. In conclusion, in vitro enzymatic amplification of both mecA and femA genes would lead to rapid and definite diagnosis of the MRSA infection.