Abstract
Klebsiella pneumoniae is an opportunistic pathogen causing nosocomial infections. Main virulence determinants of K. pneumoniae are pili, capsular polysaccharide, lipopolysaccharide, and siderophores. The histone-like nucleoid-structuring protein (H-NS) is a pleiotropic regulator found in several gram-negative pathogens. It has functions both as an architectural component of the nucleoid and as a global regulator of gene expression. We generated a Δhns mutant and evaluated the role of the H-NS nucleoid protein on the virulence features of K. pneumoniae. A Δhns mutant down-regulated the mrkA pilin gene and biofilm formation was affected. In contrast, capsule expression was derepressed in the absence of H-NS conferring a hypermucoviscous phenotype. Moreover, H-NS deficiency affected the K. pneumoniae adherence to epithelial cells such as A549 and HeLa cells. In infection experiments using RAW264.7 and THP-1 differentiated macrophages, the Δhns mutant was less phagocytized than the wild-type strain. This phenotype was likely due to the low adherence to these phagocytic cells. Taken together, our data indicate that H-NS nucleoid protein is a crucial regulator of both T3P and CPS of K. pneumoniae.
Highlights
Klebsiella pneumoniae is an opportunistic Gram-negative bacterium belonging to the Enterobacteriaceae family causing nosocomial infections such as septicemia, pneumonia, urinary tract infections, surgical site infections and catheter-related infections (Han, 1995; Podschun and Ullmann, 1998; Schelenz et al, 2007; Ares et al, 2013)
histone-like nucleoid-structuring protein (H-NS) amino acid sequences of K. pneumoniae strains were homologous to H-NS proteins of enteric bacteria such as Salmonella, Yersinia, Shigella, and E. coli (Figure 1A)
This study describes for the first time the role of H-NS in expression of K. pneumoniae virulence features
Summary
Klebsiella pneumoniae is an opportunistic Gram-negative bacterium belonging to the Enterobacteriaceae family causing nosocomial infections such as septicemia, pneumonia, urinary tract infections, surgical site infections and catheter-related infections (Han, 1995; Podschun and Ullmann, 1998; Schelenz et al, 2007; Ares et al, 2013). Numerous nosocomial outbreaks caused by multiple-drug resistant K. pneumoniae have. The main virulence determinants of K. pneumoniae are: capsular polysaccharide (CPS), lipopolysaccharide, siderophores, and pili (Gerlach et al, 1989; Podschun and Ullmann, 1998; Brisse et al, 2009). While the pili are required during the initial colonization of the host, the CPS impairs macrophage-mediated phagocytosis (Highsmith and Jarvis, 1985; Podschun and Ullmann, 1998; Alvarez et al, 2000). CPS is a complex layer of surface-associated polysaccharides which is important for the pathogenesis of K. pneumoniae in both, animal models as well as in infections of cultured cells (Cortés et al, 2002; Lawlor et al, 2005; Regueiro et al, 2006; March et al, 2013)
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