Abstract：
Using rpoS, tolC, ompF, and recA knockouts, we investigated their effect on the physiological response and lethality of ciprofloxacin in E. coli growing at different rates on glucose, succinate or acetate. We have shown that, regardless of the strain, the degree of changes in respiration, membrane potential, NAD+/NADH ratio, ATP and glutathione (GSH) strongly depends on the initial growth rate and the degree of its inhibition. The deletion of the regulator of the general stress response RpoS, although it influenced the expression of antioxidant genes, did not significantly affect the tolerance to ciprofloxacin at all growth rates. The mutant lacking TolC, which is a component of many E. coli efflux pumps, showed the same sensitivity to ciprofloxacin as the parent. The absence of porin OmpF slowed down the entry of ciprofloxacin into cells, prolonged growth and shifted the optimal bactericidal concentration towards higher values. Deficiency of RecA, a regulator of the SOS response, dramatically altered the late phase of the SOS response (SOS-dependent cell death), preventing respiratory inhibition and a drop in membrane potential. The recA mutation inverted GSH fluxes across the membrane and abolished ciprofloxacin-induced H2S production. All studied mutants showed an inverse linear relationship between logCFU ml-1 and the specific growth rate. Mutations shifted the plot of this dependence relative to the parental strain according to their significance for ciprofloxacin tolerance. The crucial role of the SOS system is confirmed by dramatic shift down of this plot in the recA mutant.
摘要：
使用rpoS,tolc,ompF,和recA淘汰赛，我们研究了环丙沙星对不同生长速率的大肠杆菌对葡萄糖的生理反应和致死率的影响,琥珀酸盐或乙酸盐。我们已经证明，不管压力如何，呼吸的变化程度，膜电位，NAD+/NADH比率，ATP和谷胱甘肽（GSH）在很大程度上取决于初始生长速率及其抑制程度。一般应激反应调节因子RpoS的缺失，尽管它影响了抗氧化基因的表达，在所有生长速率下对环丙沙星的耐受性均无显著影响。缺少TolC的突变体,它是许多大肠杆菌外排泵的组成部分，对环丙沙星的敏感性与母体相同。缺乏孔蛋白OmpF减慢了环丙沙星进入细胞的速度，延长生长，并将最佳杀菌浓度转向更高的值。RecA的缺陷，SOS响应的监管者，显著改变了SOS反应的晚期阶段（SOS依赖性细胞死亡），防止呼吸抑制和膜电位下降。recA突变逆转了跨膜的GSH通量，并消除了环丙沙星诱导的H2S产生。所有研究的突变体均显示logCFUml-1与特定生长速率之间呈反线性关系。根据其对环丙沙星耐受性的重要性，突变相对于亲本菌株改变了这种依赖性的图。SOS系统的关键作用通过recA突变体中这一情节的戏剧性下降得到证实。
