Effect of sub-minimum inhibitory concentrations of macrolides on sensitivity against nitrosative stress in Pseudomonas aeruginosa

Previous studies have reported that long-term low-dose administration of certain macrolides is efficacious in patients with persistent pulmonary Pseudomonas aeruginosa infections. In the present study, we examined the effect of sub-minimum inhibitory concentrations (sub-MICs) of macrolide antibiotics on growth, biofilm formation and sensitivity against nitrosative stress of P. aeruginosa PAO1. Sub-MICs of the 14-membered macrolides, erythromycin (EM) and clarithromycin (CAM), decreased growth and biofilm formation, and increased sensitivity against nitrosative stress of P. aeruginosa, indicating that administration of sub-MICs of the 14-membered macrolides was effective against P. aeruginosa. However, a 16-membered macrolide, josamycin (JM), was not or less effective. To investigate whether increase in macrolide exposure-dependent sensitivity against nitrosative stress was a typical characteristic of P. aeruginosa, we examined the viabilities of other P. aeruginosa strains treated with an NO donor with or without EM. In non-multidrug-resistant P. aeruginosa (non-MDRP), sub-MIC of EM significantly induced loss of viability following treatment with an NO donor. Furthermore, in high-risk clone ST235 which was a major group in multidrug-resistant P. aeruginosa (MDRP), sub-MIC of EM could effectively induce decreases of the viabilities of MDRP treated with an NO donor. These results suggest that the effect of sub-MIC macrolide treatment on the sensitivity of P. aeruginosa against nitrosative stress form one of explanations for the positive effects of long-term low-dose macrolide therapy.

既往研究显示，长期低剂量给予部分大环内酯类药物，对持续性肺铜绿假单胞菌（Pseudomonas aeruginosa，P. aeruginosa）感染患者具有确切疗效。本研究针对大环内酯类抗生素的亚最低抑菌浓度（sub-minimum inhibitory concentrations，sub-MICs）对铜绿假单胞菌PAO1的生长、生物被膜形成以及抗亚硝化应激敏感性的影响展开了探究。14元环大环内酯类的红霉素（erythromycin，EM）与克拉霉素（clarithromycin，CAM）的sub-MIC可抑制铜绿假单胞菌的生长与生物被膜形成，并增强其对亚硝化应激的敏感性，提示14元环大环内酯类sub-MIC给药可有效抑制铜绿假单胞菌。而16元环大环内酯类交沙霉素（josamycin，JM）则未表现出类似效果，或仅具有微弱作用。为明确大环内酯类暴露依赖性的亚硝化应激敏感性提升是否为铜绿假单胞菌的共性特征，我们检测了其他铜绿假单胞菌菌株在经红霉素预处理与否的情况下，经一氧化氮供体处理后的存活率。在非多重耐药铜绿假单胞菌（non-multidrug-resistant P. aeruginosa，non-MDRP）中，红霉素sub-MIC可显著诱导经一氧化氮供体处理后的菌株存活率下降。此外，在多重耐药铜绿假单胞菌（multidrug-resistant P. aeruginosa，MDRP）的主要流行高风险克隆ST235中，红霉素sub-MIC同样可有效降低经一氧化氮供体处理后的MDRP存活率。上述结果表明，sub-MIC大环内酯类给药对铜绿假单胞菌抗亚硝化应激敏感性的调控作用，可为长期低剂量大环内酯类治疗的正向疗效提供一种合理解释。