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目的：评价铜绿假单胞菌在亚抑制浓度（ SIC）的左氧氟沙星作用下毒力因子表型及基因表达的变化并探索其可能的调控途径。方法用临床标准菌株PAO1及其密度感应系统（ QS）的基因突变株，测定不同浓度下菌株生长曲线，以不影响细菌生长的最高抗菌素浓度为亚抑制浓度。分别测定各菌株在SIC的抗菌素作用下生物膜形成、绿脓菌素和鼠李糖脂的变化。用实时定量聚合酶链式反应（ RT－PCR）测定菌株毒力蛋白编码基因以及QS基因在SIC的左氧氟沙星作用下表达的变化。用生物发光法测定QS信号分子在SIC的抗菌素作用下的变化。结果在SIC的左氧氟沙星作用下，PAO1的毒力因子编码基因和QS调控基因（lasR、rhlR）表达均显著增加，PAO1野生株的毒力因子也增加，但lasR、rhlR突变株无此变化，同时QS信号分子水平也无显著变化。结论亚抑制浓度的左氧氟沙星促进铜绿假单胞菌毒力因子的产生，这一效应是通过lasR和rhlR调节实现的，但这一调控作用可能并不是直接通过AHL信号分子完成。“,”Objective To explore the effect of levofloxacin on the viru-lence factors of Pseudomonas aeruginosa at subinhibitory concentration ( SIC) and gene expression as well as the potential regulatory approa-ches.Methods Pseudomonas aeruginosa PAO1 and lasR/rhlR mutant strains of its quorum sensing ( QS ) were grown in SIC of levofloxacin.Strains growth curves were measured at different concentrations, and the highest concentration of antibiotic without affecting bacterial growth was considered as SIC.The biofilm formation, pyocyanin and rhamnolipid production were determined.The real -time quantitative PCR ( RT -PCR) method was adopted to determine virulence protein coding genes and expression changes of QS genes under SIC of levofloxacin.The level of QS signals were determined by bioluminescence assay.Results The expression of genes coding for virulence factor, for example, lasB and rhlA, were up-regulated in response to SIC of levofloxacin.The expres-sion of regulators in QS system increased significantly in the presence of levofloxacin, with a growing production of virulence factors in PAO1 wild type strain.But there were no significant changes in the production of biofilm and pyocyanin for lasR or rhlR mutant strain.No significant change of N-acyl-homoserine lactone( AHL) signal level was observed on SIC of levofloxacin.Conclusion SIC of levofloxacin augments virulence production in Pseudomonas aeruginosa through the regulations of lasR and rhlR, but this regulation may not be achieved directly through AHL signals.