Medicinal Plants from Indian Subcontinent Decrease Quorum sensing Dependent Virulence in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa (PAO1), an opportunistic pathogen in immune compromised patients is under the regulation of the LasR-RhlR system for quorum sensing (QS) mediated development of virulence. Natural products have recently become a promising source for deriving molecules that can potentially inhibit QS. Medicinal plants from Indian subcontinent used in traditional medicine are well known for their antimicrobial effects on a variety of human pathogens. However, few studies have investigated its QS related antivirulent activities. Our objective was to screen for the QS inhibitory properties of 16 high quality ayurvedic medicinal plants derived from Indian sub-continent, understand their mechanism of action and investigate their effect on the expression of QS regulated virulence factors in PAO1. QS inhibition of sub-lethal concentrations (SLC) of plant extracts was measured in violacein producing Chromobacterium violaceum bioassay model. Effect of these extracts on PAO1 virulent factors pyocyanin, elastase and total protease were quantified by standard protocols. Results indicated that all extracts reduced violacein production significantly. The results from modified screening assay suggested the primary mechanism of QSI was a combination of (1) reduction in AI formation and (2) inhibition of AI activity. The extracts reduced pyocyanin synthesis, inhibited the activity of elastase and other proteolytic enzymes.