背景:自从发现许多细菌产生吲哚以来,已经过去了一个多世纪,但是对这种分子的实际生物学作用的研究才刚刚开始。在产生吲哚的细菌如大肠杆菌中广泛研究了吲哚对细菌毒力的影响。为了更深入地理解它的功能作用,这项研究调查了在大肠杆菌固定相培养上清液中发现的0.5-1.0mM浓度的吲哚如何能够改变非吲哚产生细菌的毒力,比如铜绿假单胞菌,变形杆菌,和肺炎克雷伯菌,在大肠杆菌混合感染中自然暴露于吲哚。
结果:生物膜形成,抗菌敏感性,和外排泵活性是评估的三个表型测试。吲哚被发现对铜绿假单胞菌的抗生素敏感,奇异变形杆菌和肺炎克雷伯菌对环丙沙星,亚胺培南,头孢曲松,头孢他啶,和阿米卡星通过显著降低MIC,倍数变化范围从4到16。在32/45铜绿假单胞菌和所有8种奇异变形杆菌中,生物膜的产生被部分消除,而在30/40肺炎克雷伯菌中观察到诱导的生物膜产生。此外,acrAB和oqxAB,使用定量实时(qRT)-PCR对5种肺炎克雷伯菌分离物中的4种负责耐药结瘤分裂多药外排泵的基因进行了基因型研究。这表明,与对照组相比,在吲哚处理的分离株中,所有四个基因表现出2^-ΔΔCT<1所示的降低的表达。
结论:外排泵表达的qRT-PCR研究结果建立了一种新的明确的分子机制相关性,该机制位于吲哚对细菌抗生素耐受性的影响之下。这项研究为吲哚信号的各种机制和多种生物学功能以及它如何影响非吲哚产生细菌的致病性提供了新的视角。
BACKGROUND: More than a century has passed since it was discovered that many bacteria produce indole, but research into the actual biological roles of this molecule is just now beginning. The influence of indole on bacterial virulence was extensively investigated in indole-producing bacteria like Escherichia coli. To gain a deeper comprehension of its functional role, this study investigated how indole at concentrations of 0.5-1.0 mM found in the supernatant of Escherichia coli stationary phase culture was able to alter the virulence of non-indole-producing bacteria, such as Pseudomonas aeruginosa, Proteus mirabilis, and Klebsiella pneumoniae, which are naturally exposed to indole in mixed infections with Escherichia coli.
RESULTS: Biofilm formation, antimicrobial susceptibility, and efflux pump activity were the three phenotypic tests that were assessed. Indole was found to influence antibiotic susceptibly of Pseudomonas aeruginosa, Proteus mirabilis and Klebsiella pneumoniae to ciprofloxacin, imipenem, ceftriaxone, ceftazidime, and amikacin through significant reduction in MIC with fold change ranged from 4 to 16. Biofilm production was partially abrogated in both 32/45 Pseudomonas aeruginosa and all eight Proteus mirabilis, while induced biofilm production was observed in 30/40 Klebsiella pneumoniae. Moreover, acrAB and oqxAB, which encode four genes responsible for resistance-nodulation-division multidrug efflux pumps in five isolates of Klebsiella pneumoniae were investigated genotypically using quantitative real-time (qRT)-PCR. This revealed that all four genes exhibited reduced expression indicated by 2^-ΔΔCT < 1 in indole-treated isolates compared to control group.
CONCLUSIONS: The outcomes of qRT-PCR investigation of efflux pump expression have established a novel clear correlation of the molecular mechanism that lies beneath the influence of indole on bacterial antibiotic tolerance. This research provides novel perspectives on the various mechanisms and diverse biological functions of indole signaling and how it impacts the pathogenicity of non-indole-producing bacteria.