Klebsiella pneumoniae is considered the most clinically relevant species of Enterobacteriaceae, known to cause severe infections including liver abscesses. To the best of our knowledge, a large proportion of iron in the human body is accumulated and stored in the liver. We hypothesize that increased iron availability is an important factor driving liver abscess formation and we therefore aim to understand the effects of iron on K. pneumoniae causing liver abscesses. All tested K. pneumoniae clinical isolates, including those isolated from liver abscesses and other abdominal invasive infection sites, grew optimally when cultured in LB broth supplemented with 50 μM iron and exhibited the strongest biofilm formation ability under those conditions. Decreased growth and biofilm formation ability were observed in all tested strains when cultured with an iron chelator (P < 0.05). The infection model of G. mellonella larvae indicated the virulence of liver abscess-causing K. pneumoniae (2/3) cultured in LB broth with additional iron was significantly higher than those under iron-restricted conditions (P < 0.05). The relative expression levels of the four siderophore genes (iucB, iroB, irp1, entB) in K. pneumoniae strains isolated from liver abscesses cultured with additional iron were lower than those under iron-restricted conditions (P < 0.05). It is suggested by our research that iron in the environment can promote growth, biofilm formation and enhance virulence of K. pneumoniae causing liver abscesses. A lower expression of siderophore genes correlates with increased virulence of liver abscess-causing K. pneumoniae. Further deeper evaluation of these phenomena is warranted.

中文翻译：

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铁对引起肝脓肿的肺炎克雷伯菌的生长，生物膜形成和毒力的影响。

肺炎克雷伯菌被认为是临床上与肠杆菌科最相关的物种，已知会引起包括肝脓肿在内的严重感染。据我们所知，人体中很大一部分铁被积累并储存在肝脏中。我们假设铁的可用性增加是驱动肝脓肿形成的重要因素，因此我们旨在了解铁对引起肝脓肿的肺炎克雷伯菌的影响。当在补充有50μM铁的LB肉汤中培养时，所有测试的肺炎克雷伯菌临床分离株，包括从肝脓肿和其他腹部侵袭性感染部位分离得到的分离株，均能最佳生长，并在这些条件下表现出最强的生物膜形成能力。用铁螯合剂培养时，在所有测试菌株中均观察到生长和生物膜形成能力下降（P <0.05）。G. mellonella幼虫的感染模型表明，在含其他铁的LB肉汤中培养的引起肝脓肿的肺炎克雷伯菌（2/3）的毒力显着高于铁限制条件下的猪（P <0.05）。从用额外铁培养的肝脓肿分离出的肺炎克雷伯菌中，四个铁载体基因（iucB，iroB，irp1，entB）的相对表达水平低于铁限制条件下的表达水平（P <0.05）。我们的研究表明，环境中的铁可促进肺炎克雷伯菌的生长，生物膜形成并增强其毒性，从而引起肝脓肿。铁载体基因的较低表达与引起肝脓肿的肺炎克雷伯菌的致病力增加有关。必须对这些现象进行更深入的评估。