Intercellular communication is a crucial process for the multicellular community in both prokaryotes and eukaryotes. Indole has been recognized as a new member of the signal molecules which enables the regulated control of various bacterial phenotypes. To elucidate the inter-species relationship among enteric microorganisms via indole signaling, Klebsiella pneumoniae (KP) culture was treated with indole solution and examined for the pathogenicity by using various phenotypic tests. Both synthetic and naturally-produced indole preparations had no deteriorating effect on growth and autoaggregative capacity of KP. The results showed that biofilm formation of carbapenem-susceptible K. pneumoniae (KP-S) was clearly induced by indole exposure (≈ 2–10 folds), whereas no significant difference was observed in the resistant counterpart. In addition, the tolerance to β-lactam antibiotics of KP was altered upon exposure to indole and/or derivatives assessed by Kirby–Bauer disk diffusion test. Taken together, our finding indicates the functional role of indole in changing or modulating pathogenic behaviors of other bacteria.

中文翻译：

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吲哚及其衍生物调节肺炎克雷伯菌的生物膜形成和抗生素耐受性。

细胞间通讯是原核生物和真核生物多细胞群落的关键过程。吲哚已被认为是信号分子的新成员，能够调节控制各种细菌表型。为了通过吲哚信号传导阐明肠道微生物之间的种间关系，用吲哚溶液处理肺炎克雷伯菌(KP) 培养物，并通过各种表型测试检查其致病性。合成和天然产生的吲哚制剂对 KP 的生长和自聚集能力均没有恶化作用。结果表明，碳青霉烯类易感克雷伯菌的生物膜形成。肺炎链球菌(KP-S) 明显是由吲哚暴露诱导的（约 2-10 倍），而在耐药对应物中没有观察到显着差异。此外，KP 对 β-内酰胺类抗生素的耐受性在暴露于吲哚和/或通过柯比-鲍尔纸片扩散试验评估的衍生物后发生改变。综上所述，我们的发现表明吲哚在改变或调节其他细菌的致病行为中的功能作用。