Effects of iron on the growth, biofilm formation and virulence of Klebsiella pneumoniae causing liver abscess

Tao Chen,Qing Wu,Xiucai Zhang,Tieli Zhou,Siqin Zhang,Yajie Zhao,Jianming Cao,Guofeng Dong

doi:10.1186/s12866-020-01727-5

Abstract

BackgroundKlebsiella 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.ResultsAll 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).ConclusionsIt 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.

Highlights

Klebsiella pneumoniae is considered the most clinically relevant species of Enterobacteriaceae, known to cause severe infections including liver abscesses
The growth of all tested strains in the iron-restricted environment caused by the iron chelating agent was worse (P < 0.05) (Fig. 1)
We further found that iron promotes biofilm formation of K. pneumoniae in a concentrationdependent manner

Summary

Introduction

Klebsiella pneumoniae is considered the most clinically relevant species of Enterobacteriaceae, known to cause severe infections including liver abscesses. Klebsiella pneumoniae is considered the most clinically relevant species of Enterobacteriaceae, known to cause both community-acquired and nosocomial infections, including liver abscesses, pneumonia, urinary tract infections and bacteremia worldwide [1]. In the past two decades, a distinct hypervirulent variant of K. pneumoniae, characterized by its hypermucoviscous phenotype, was firstly isolated from liver abscesses in Asia and has emerged as a clinically significant pathogen responsible for highly invasive infections [2]. The pathogenicity of K. pneumoniae mainly arise from various virulence factors which allow it to overcome innate host immunity and to maintain infection in a mammalian host. The main virulence factors that play an important role in pathogenicity are capsular polysaccharide, lipopolysaccharide, pili and siderophores [4].

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