[Study on the correlation between resistance phenotype and expression level of femA of Staphylococcus aureus].

Objective: To detect the expression level of femA of Staphylococcus aureus strains with different phenotype.

Methods: 15 strains of the non-beta-lactamase-producing clinical isolates with different phenotype by agar dilution and by nitrocephin paper strip method were chosen as the object of test, in addition to 4 donative strains (BB270, BB308, BB586, COL). Total RNA were extracted and analysed by agarose gel electrophoresis. Real time fluorescent quantitative PCR was performed to quantify the expression of femA gene. The expression level of femA of BB270 was set to be standard(100%).

Results: The expressions of femA were observed in all the tested strains. The amount of femA-specific mRNA in the mutant strain BB308 was approximately 37.82% and that of stain BB586 was 240.50%, homogeneous resistant strain COL was 862.61%. The amounts in MSSA strains were from 0.00353% to 29.92%, that in low-level MRSA strains were from 0.00554% to 310%, otherwise that in high-level MRSA strains were from 13.88% to 55000%, which were different among these groups. There was no significant difference in amount of femA-mRNA between MSSA and low-level MRSA strains (P1 = 0.83) but marked between high-level MRSA and low-level MRSA/MSSA strains (P2 = 0.006, P3 = 0.01)).

Conclusion: Expression level of femA in high-level MRSA was significant higher than that in low-level MRSA and MSSA. femA was essential for the expression of high-level methicillin resistance in MRSA.