DataSheet_1_Temperatures above 37°C increase virulence of a convergent Klebsiella pneumoniae sequence type 307 strain.docx

BackgroundConvergence of Klebsiella pneumoniae (KP) pathotypes has been increasingly reported in recent years. These pathogens combine features of both multidrug-resistant and hypervirulent KP. However, clinically used indicators for hypervirulent KP identification, such as hypermucoviscosity, appear to be differentially expressed in convergent KP, potential outbreak clones are difficult to identify. We aimed to fill such knowledge gaps by investigating the temperature dependence of hypermucoviscosity and virulence in a convergent KP strain isolated during a clonal outbreak and belonging to the high-risk sequence type (ST)307.
MethodsHypermucoviscosity, biofilm formation, and mortality rates in Galleria mellonella larvae were examined at different temperatures (room temperature, 28°C, 37°C, 40°C and 42°C) and with various phenotypic experiments including electron microscopy. The underlying mechanisms of the phenotypic changes were explored via qPCR analysis to evaluate plasmid copy numbers, and transcriptomics.
ResultsOur results show a temperature-dependent switch above 37°C towards a hypermucoviscous phenotype, consistent with increased biofilm formation and in vivo mortality, possibly reflecting a bacterial response to fever-like conditions. Furthermore, we observed an increase in plasmid copy number for a hybrid plasmid harboring carbapenemase and rmpA genes. However, transcriptomic analysis revealed no changes in rmpA expression at higher temperatures, suggesting alternative regulatory pathways.
ConclusionThis study not only elucidates the impact of elevated temperatures on hypermucoviscosity and virulence in convergent KP but also sheds light on previously unrecognized aspects of its adaptive behavior, underscoring its resilience to changing environments.

研究背景：近年来，肺炎克雷伯菌（Klebsiella pneumoniae, KP）致病型的融合现象报道日益增多。此类病原菌同时兼具多重耐药与高毒力肺炎克雷伯菌的特征。然而，当前用于高毒力KP鉴定的临床指标（如高黏液表型（hypermucoviscosity））在融合型KP中呈现差异表达，导致潜在的暴发克隆株难以识别。本研究旨在填补这一认知空白，针对一次克隆暴发中分离得到的、属于高风险序列型307（sequence type 307, ST307）的融合型KP菌株，探究其高黏液表型与毒力的温度依赖性。
研究方法：本研究在不同温度（室温、28℃、37℃、40℃及42℃）下，通过包括电子显微镜在内的多种表型实验，检测了该菌株的高黏液表型、生物膜形成能力以及大蜡螟（Galleria mellonella）幼虫的致死率。为探究表型变化的潜在分子机制，本研究通过定量PCR（quantitative PCR, qPCR）分析质粒拷贝数，并结合转录组学（transcriptomics）开展相关研究。
研究结果：本研究结果显示，当培养温度高于37℃时，菌株会发生温度依赖性表型转换，呈现高黏液表型，这一现象与生物膜形成能力增强以及大蜡螟幼虫体内致死率升高相一致，或可反映细菌对发热样环境的适应性响应。此外，我们观察到携带碳青霉烯酶（carbapenemase）基因与rmpA基因的杂合质粒的拷贝数随温度升高而增加。然而，转录组学分析显示，高温环境下rmpA基因的表达水平并未发生显著变化，这提示存在其他未知的调控通路。
研究结论：本研究不仅阐明了高温环境对融合型KP高黏液表型与毒力的调控作用，还揭示了其适应性行为中此前未被认知的层面，突显了该菌株对环境变化的适应韧性。