大肠杆菌临床分离株多重耐药过程中的主动外排机制

目的　探讨临床分离大肠杆菌多重耐药机制。方法　应用荧光法测定临床分离大肠杆菌对环丙沙星的主动外排功能 ;PCR及Southernblot测定主动外排系统AcrAB结构基因acrAB ;RT PCR测定acrAB表达水平 ;自动荧光测序法测定acrAB基因扩增产物DNA序列。结果　临床分离大肠杆菌多重耐药株细胞内环丙沙星稳态浓度显著低于敏感株 (0 .73mg/L± 0 .0 4mg/L比 2 .0 0mg/L± 0 .0 7mg/LA660 ,P <0 .0 0 1) ;临床分离大肠杆菌无acrAB缺失 ;多重耐药株acrAB表达水平显著高于其他菌株 ;多重耐药株以及敏感株acrAB基因扩增产物无点突变和缺失。结论　主动外排系统acrAB的高表达导致临床分离大肠杆菌产生多重耐药性 ;acrAB的表达可能受多重耐药操纵子调控。

Active efflux of antibiotics as multiple-antibiotic-resistance mechanism in clinical strains of escherichia coli

OBJECTIVE: To investigate multiple-antibiotic-resistance mechanism in clinical strains of Escherichia coli. METHODS: Accumulation of ciprofloxacin in clinical isolates of Escherichia coli was measured by fluorometry, and acrAB gene was identified by PCR and Southern blot. The levels of acrAB gene expression were measured by RT-PCR. DNA fragments were sequenced by automated fluorescence sequencing. RESULTS: The state concentration of ciprofloxacin in multiple-antibiotic-resistant (Mar) strains was significantly lower than that in susceptible stsains (0.73 mg/L +/- 0.04 mg/L vs 2.00 mg/L +/- 0.07 mg/L A(660), P < 0.001). The level of acrAB gene expression in Mar strains was significantly higher than that in other strains. No deletion or point mutation in acrAB gene were found in Mar and susceptible clinical Escherichia coli isolates. CONCLUSIONS: High expression of acrAB gene leads to multiple-antibiotic-resistance in clinical strains of Escherichia coli, and Mar operon may contribute to the regulation of acrAB gene expression.