Klebsiella pneumoniae triggers a cytotoxic effect on airway epithelial cells.
BACKGROUND
Klebsiella 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.


RESULTS
The 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.


CONCLUSIONS
Our 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.
Cano
Victoria
V
Fundación Caubet-CIMERA, Programa de Infección e Inmunidad, Recinto Hospital Joan March, carretera Sóller, km 12, 07110, Bunyola, Spain. victoria.cano@caubet-cimera.es
Moranta
David
D
Llobet-Brossa
Enrique
E
Bengoechea
José Antonio
JA
Garmendia
Junkal
J
D000818:Animals; D016667:Bacterial Capsules / Q000502:physiology; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000382:microbiology*; D005260:Female; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology*; D007711:Klebsiella pneumoniae / Q000472:pathogenicity*; D008168:Lung / Q000166:cytology / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D011135:Polysaccharides, Bacterial / Q000502:physiology; D014774:Virulence
D011135:Polysaccharides, Bacterial