Biofilm of Klebsiella pneumoniae minimize phagocytosis and cytokine expression by macrophage cell line

Abstract

Infectious bacteria in biofilm mode are involved in many of persistent infections. Owing to its importance in clinical settings many in vitro and in vivo studies have analysed the structural and functional properties of biofilm, its resistance to antibiotic exposure etc. Currently the immune mechanism toward the clearance of biofilm infections is being investigated. K. pneumoniae is one of the major leading causes of biofilm infections on indwelling medical devices. There was no previous literature that demonstrates the interactions of macrophage cells lines and Klebsiella biofilm, as the first report, we investigated the in vitro response of Klebsiella biofilm to phagocytosis and cytokine expression. We developed an in vitro model to study the interactions of Kebsiella biofilm and macrophage. The phagocytosis assay was performed for heat inactivated and live biofilm. A similar phagocytic response against both biofilms were observed when these cells were exposed to RAW 264.7 macrophages. Also, the expressions of TLR2, iNOS, inflammatory cytokines such as IL-{beta}1, IFN-{gamma}, IL-6, IL-12, IL-4, TNF- and anti-inflammatory cytokines, IL-10 during phagocytosis were analysed. These results collectively demonstrated that the rate of phagocytosis was an average of 15% for both biofilms. Also, when activated macrophage was exposed to heat-inactivated or live biofilms, there was a significant increase in proinflammatory cytokine genes together with expected increase in TLR2 and iNOS. Thus, it is clear that macrophage response against biofilm producing K. pneumoniae results in increase in phagocytic rate and a corresponding increase in inflammatory cytokine gene expression which could be important for clearing K. pneumoniae cells.