Abstract
BackgroundKlebsiella pneumoniae is a capsulated Gram negative bacterial pathogen and a frequent cause of nosocomial infections. Despite its clinical relevance, little is known about the features of the interaction between K. pneumoniae and lung epithelial cells on a cellular level, neither about the role of capsule polysaccharide, one of its best characterised virulence factors, in this interaction.ResultsThe interaction between Klebsiella pneumoniae and cultured airway epithelial cells was analysed. K. pneumoniae infection triggered cytotoxicity, evident by cell rounding and detachment from the substrate. This effect required the presence of live bacteria and of capsule polysaccharide, since it was observed with isolates expressing different amounts of capsule and/or different serotypes but not with non-capsulated bacteria. Cytotoxicity was analysed by lactate dehydrogenase and formazan measurements, ethidium bromide uptake and analysis of DNA integrity, obtaining consistent and complementary results. Moreover, cytotoxicity of non-capsulated strains was restored by addition of purified capsule during infection. While a non-capsulated strain was avirulent in a mouse infection model, capsulated K. pneumoniae isolates displayed different degrees of virulence.ConclusionOur observations allocate a novel role to K. pneumoniae capsule in promotion of cytotoxicity. Although this effect is likely to be associated with virulence, strains expressing different capsule levels were not equally virulent. This fact suggests the existence of other bacterial requirements for virulence, together with capsule polysaccharide.
Highlights
Klebsiella pneumoniae is a capsulated Gram negative bacterial pathogen and a frequent cause of nosocomial infections
We show for the first time that K. pneumoniae exerts a cytotoxic effect on airway epithelial cells that is associated with the presence of com/1471-2180/9/156 sule polysaccharide (CPS)
K. pneumoniae induces a cytotoxic effect in lung epithelial cells A549 lung epithelial cells were infected with K. pneumoniae 52145 (52145), a highly capsulated strain (339 μg per 105 c.f.u.) for 5 h with different multiplicity of infection (MOI) and the host actin cytoskeleton was stained
Summary
Klebsiella pneumoniae is a capsulated Gram negative bacterial pathogen and a frequent cause of nosocomial infections. Little is known about the features of the interaction between K. pneumoniae and lung epithelial cells on a cellular level, neither about the role of capsule polysaccharide, one of its best characterised virulence factors, in this interaction. BMC Microbiology 2009, 9:156 http://www.biomedcentral.com/1471-2180/9/156 sule polysaccharide (CPS), siderophores, lipopolysaccharide (LPS) and adhesins are virulence factors identified for this pathogen. Most of the studies have focused on the role of CPS in Klebsiella virulence. Similar to CPSs from other pathogens, Klebsiella CPS is responsible for resistance to complement mediated killing [7] and impedes adhesion to and invasion of epithelial cells [8] by sterically preventing receptor-target recognition of bacterial adhesins [9,10]. We have demonstrated that CPS mediates resistance to antimicrobial peptides (APs), trapping APs and acting as a bacterial decoy [11,12]
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