Quorum Sensing and Biofilm Formation in Microbial Pathogenesis
When encountering a new host, every potential microbial pathogen can stay, acquire nutrients, colonize and then seek another host. Alternatively the pathogen could express its full battery of virulence factors, and invade the host. The successful attack of a host is now understood to be a communal process called Quorum Sensing (QS). Utilizing QS, pathogens employ a series of chemical signals and sensing systems that jointly engage bacteria to switch from acting as individual cells to operating in a concerted multicellular fashion. QS is the capacity to detect extracellular, small-molecule signals and to subsequently alter gene expression in response to bacterial population densities. The QS systems of bacteria are now known to serve a wide variety of functions beyond a simple estimate of cell density. Some of the processes controlled by QS include bioluminescence and expression of virulence factor(s). Furthermore, QS also plays a pivotal role in the production of healthy and fully developed biofilms which are complex and stable multi-layered structures with defined architecture, in which bacterial communities exist in a sessile form.Many gram positive and gram negative pathogenic bacteria uses QS to control virulence and biofilm formation. A major challenge presented by biofilms is that bacteria living within them enjoy increased protection against host immune responses and are distinctly more tolerant to various anti-microbial treatments. Targeting QS systems, which orchestrate important sequential events during the infection process has afforded a novel opportunity to tackle bacterial infection by a means other than growth inhibition. Since inhibiting the QS system does not threaten bacteria with a ‘life-or-death’ situation, it is less likely to yield resistant phenotypes. The present study is focused on the opportunistic pathogen, Pseudomonas aeruginosa which is a metabolically versatile, clinically important pathogen, responsible for an array of severe opportunistic infections and is therefore a model organism to identify inhibitors of Quorum Sensing and biofilm formation from natural resources. In vitro studies using inhibitors from natural sources like clove bud oil(CBO) in P. aeruginosa, revealed a concentration dependent attenuation of a variety of virulence factors including motility, extracellular DNA, exopolysaccharides and pigment production.