Antimicrobial Discovery Center, Department of Biology, Northeastern University, Boston, Massachusetts, USA.
Antimicrob Agents Chemother. 2012 Sep;56(9):4922-6. doi: 10.1128/AAC.00921-12. Epub 2012 Jul 9.
Persisters are dormant phenotypic variants of regular cells that are tolerant to antibiotics and play an important role in recalcitrance of chronic infections to therapy. Persisters can be produced stochastically in a population untreated with antibiotics. At the same time, a deterministic component of persister formation has also been documented in a population of cells with DNA damaged by fluoroquinolone treatment. Expression of the SOS response under these conditions induces formation of persisters by increasing expression of the TisB toxin. This suggests that other stress responses may also contribute to persister formation. Of particular interest is oxidative stress that pathogens encounter during infection. Activated macrophages produce reactive oxygen and nitrogen species which induce the SoxRS and OxyR regulons. Genes controlled by these regulons deactivate the oxidants and promote repair. We examined the ability of oxidative stress induced by paraquat (PQ) to affect persister formation. Preincubation of cells with PQ produced a dramatic increase in the number of persisters surviving challenge with fluoroquinolone antibiotics. PQ did not affect killing by kanamycin or ampicillin. Persisters in a culture treated with PQ that survived a challenge with a fluoroquinolone were also highly tolerant to other antibiotics. PQ induces SoxRS, which in turn induces expression of the AcrAB-TolC multidrug-resistant (MDR) pump. Fluoroquinolones are extruded by this MDR pump, and the effect of PQ on antibiotic tolerance was largely abolished in a mutant that was defective in the pump. It appears that PQ, acting through AcrAB-TolC, reduces the concentration of fluoroquinolones in the cells. This allows a larger fraction of cells to become persisters in the presence of a fluoroquinolone. Analysis of a lexA3 mutant indeed showed a dependence of persister induction under these conditions on SOS. These findings show that induction of a classical resistance mechanism, MDR efflux, by oxidative stress leads to an increase in multidrug-tolerant persister cells.
持久型细菌是常规细胞的休眠表型变异体，对抗生素具有耐受性，并在慢性感染对治疗的抗性中发挥重要作用。在未使用抗生素处理的群体中，持久型细菌可以随机产生。同时，在经氟喹诺酮类药物处理导致 DNA 受损的细胞群体中，也记录到了持久型细菌形成的确定性成分。在这些条件下，SOS 反应的表达通过增加TisB 毒素的表达诱导持久型细菌的形成。这表明其他应激反应也可能有助于持久型细菌的形成。特别值得关注的是病原体在感染过程中遇到的氧化应激。激活的巨噬细胞会产生活性氧和氮物种，从而诱导 SoxRS 和 OxyR 调控子。受这些调控子控制的基因会使氧化剂失活并促进修复。我们研究了百草枯 (PQ) 诱导的氧化应激对持久型细菌形成的影响。细胞预先用 PQ 孵育会显著增加经受氟喹诺酮类抗生素挑战后存活的持久型细菌数量。PQ 不影响庆大霉素或氨苄青霉素的杀菌作用。用 PQ 处理的培养物中存活下来经受氟喹诺酮类抗生素挑战的持久型细菌对其他抗生素也具有高度耐受性。PQ 诱导 SoxRS，进而诱导 AcrAB-TolC 多药耐药 (MDR) 泵的表达。氟喹诺酮类药物通过该 MDR 泵被排出，在泵缺陷突变体中，PQ 对抗生素耐受性的影响在很大程度上被消除。看来 PQ 通过 AcrAB-TolC 作用降低了细胞内氟喹诺酮类药物的浓度。这使得在存在氟喹诺酮类药物的情况下，更大比例的细胞成为持久型细菌。在这些条件下，对 lexA3 突变体的分析确实表明，诱导持久型细菌的形成依赖于 SOS。这些发现表明，氧化应激诱导经典的耐药机制，MDR 外排，会导致多药耐药的持久型细菌增加。
