Preliminary Study On Resistant Mechanisms Of Staphylococcus Epidermidis To Fluoroquinolones

Objective:To understand the resistant mechanisms of Staphylococcus epidermidis to fluoroquinolones by studying the correlation of the function and gene expression of active efflux transporter in Staphylococcus epidermidis.To give references for inhabiting Staphylococcus epidermidis resistant to antibiotics.Methods:(1)Clinical strains of Staphylococcus epidermidis were collected,antibiotic sensitive test wasconducted by means of disc diffusion method(Kirby-Bauer),and resistant strains and sensitive strains were selected,standard strains ATCC 12228 were regarded as control. (2)NorA gene in all clinical Staphylococcus epidermidis were amplified by means of PCR,the nucleotide sequences were analyzed by sequencing. (3)The total RNA were extracted from Staphylococcus epidermidis,and the expression levels of norA gene was analyzed by Real-time fluorogenetic quantitative PCR;and the expression of norA between the sensitive and resistant group were compared.(4)The accumulation of ofloxacin in Staphylococcus epidermidis and the effects of NaN₃ on accumulation were measured by a fluorescence method.Results:(1)Clinical isolates of Staphylococcus epidermidis had a higher rate of fluoroquinolones resistance,more than 80%of them were resistant to one or more fluoroquinolones.(2)The norA gene was detected in 48 Staphylococcus epidermidis strains,the positive rate was 98%. Sequence comparison revealed that three resistant strains contained nucleotide 386-C bp deletion.(3)The expression levels of norA gene in resistant strains was obviously higher than those in sensitive strains with significant difference(P<0.05).(4)The steady-state accumulation concentration of ofloxacin fluoroquinolones sensitive organisms was higher than that of resistant strains with significant difference(P<0.05), NaN₃ had different influence on accumulation concentration of different strains and the effect on that of SE40 was the most obvious;After adding sodium azide,the accumulation of ofloxacin in intracellular increased.Conclusion:There was obvious cross-resistance to fluoroquinolones in Staphylococcus epidermidis,to remind clinicians using antibiotics correctly to reduce the emergence of drug-resistant strains.The increase of expression level of norA and the effiuxing enhanced lead to the decreasing of the accumulation of fluoroquinolones,which may be an important reason of Staphylococcus epidermidis resistant to fluoroquinolones.The deletion of 386-C bp in promoter region of norA may be also associated with higher levels of norA gene transcription.