The role of femA regulating gene on methicillin-resistant Staphylococcus aureus clinical isolates

The authors investigated the role of femA regulating gene on methicillin-resistant Staphylococcus aureus (MRSA).

High-level MRSA, low-level MRSA, and methicillin-susceptible Staphylococcus aureus (MSSA) were determined by agar diffusion methods. β-lactamase was then detected by nitrocefin and the presence of mecA was determined by PCR. Only β-lactamase-negative but mecA-positive isolates were included in further studies. The femA gene and its 250 bp upstream sequence were amplified by PCR. Expression levels of femA were determined by real-time fluorescent quantitative PCR. The 250 bp upstream sequence of femA was labeled by BrightStar Psoralen-Biotin and was detected by electrophoretic mobility shift assay (EMSA).

The expression levels of femA in the three different groups (MSSA, low-level MRSA, and high-level MRSA) ranged from 3.53×10-3% to 29.91%, 5.54×10-3% to 3.1×102%, and 13.88% to 5.50×104%, respectively. EMSA could detect the signal shift in 55 high-level MRSA isolates but not in four low-level MRSA and four MSSA strains.

The expression levels of femA in high-level MRSA (non-β-lactamase-producing) were higher than in low-level MRSA and MSSA. The femA regulating gene probably lies in the 250 bp upstream sequence in MRSA. High-level expression of femA seems to be essential for high-level MRSA.