[The correlation between expression level of femB and resistance phenotype of methicillin-resistant Staphylococcus aureus (MRSA)].

ABSTRACT

OBJECTIVE: To investigate the correlation between the phenotype and expression level of femB of Staphylococcus aureus (MRSA), to discuss the mechanism of different phenotypes in methicillin-resistant Staphylococcus aureus. METHODS: The minimal inhibitory concentrations (MICs) of oxacillin against 71 clinical isolates of Staphylococcus aureus were determined by agar dilution method according to NCCLS. The production of beta-lactamase was identified by Cefinase paper strip method. The isolation rate of beta-lactamase-producing strains was counted and the correlation between the resistance phenotype and isolation rate of beta-lactamase was analysed by statistics. Real time fluorescent quantitative PCR was used to quantify the mRNA expression of femB of non-beta-lactamase-producing strains. RESULTS: The resistance rate of 71 Staphylococcus aureus to oxacillin was 66.20% (47/71), the isolation rate of beta-lactamase-producing MSSA strains was 58.3%,and that of strains of high- and low-level resistance to oxacillin were 63.15% and 55.56%. The standard curve was performed by series dilution of the heterogeneous resistant strain BB270, and the amount of femB-specific mRNA in strain BB270 was set to be 1. The calculated femB amounts in MSSA strains were from 0.4830-3.3636, while the amounts were from 0.4204-3.3636 in low-level MRSA strains, and 0.0718-16.0000 in high-level MRSA strains. There were no difference in the level of femB among MSSA, high-level MRSA and low-level MRSA. CONCLUSION: The expression level of femB may not be related to the resistance of non-beta-lactamase-producting Staphylococcus aureus to methicillin.