The role of capsules in Klebsiella pneumoniae biofilm formation

Abstract number: 1134_03_423

Struve C., Molin S., Krogfelt K.A.


K. pneumoniae is an important opportunistic pathogen and frequent cause of hospital infections. K. pneumoniae cells are characteristically surrounded by a pronounced polysaccharide capsule, which has been proven to be an important virulence factor for the bacteria. The ability of bacteria to form biofilms is recognized to play a role in the pathogenicity of many bacterial species. In biofilms bacteria are organised in micro-colonies embedded in a matrix of exo-cellular polymeric substances (EPS). The EPS is considered to stabilize the biofilm structure and protect the bacteria against host defence mechanisms and the actions of antibiotics. In this study we investigate the role of the polysaccharide capsule on K. pneumoniae biofilm formation.


The gene-cluster encoding the synthesis of the K16 capsule was cloned and sequenced from the clinical K. pneumoniae isolate 3091, and an isogenic non-capsulated mutant was constructed. The wildtype and mutant were tagged chromosomally with fluorescent markers and grown in continuous flow-cell systems to characterize their biofilm formation using confocal laser scanning microscopy.


The wildtype stain was found to form thick irregularly shaped biofilms. The biofilms mainly consisted of loose clusters of bacteria, up to 40 mm thick. Although the biofilm covered most of the substratum, open areas were also present within and between the bacterial clusters. The non-capsulated mutant was also able to form biofilms; however the architecture differed from that of the wildtype. The non-capsulated mutant spread as a confluent thin layer of cells covering the substratum. The vast majority of the biofilm was less than 5 mm thick, and only occasionally thicker bacterial clusters resembling the wildtype biofilm phenotype were observed.


K. pneumoniae cells are able to form thick biofilms when grown in continuous flow systems. The polysaccharide capsule was not found to be essential for biofilm formation per se but its absence significantly affected biofilm development and architecture. Future studies may reveal the influence of capsules on biofilm resistance against host defence systems and actions of antibiotics.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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