Ellagic Acid Derivatives from <em>Terminalia chebula</em> Retz. Downregulate the Expression of Quorum Sensing Genes to Attenuate <em>Pseudomonas aeruginosa</em> PAO1 Virulence
<div><h3>Background</h3><p>Burgeoning antibiotic resistance in <em>Pseudomonas aeruginosa</em> has necessitated the development of anti pathogenic agents that can quench acylhomoserine lactone (AHL) mediated QS with least risk of resistance. This study explores the anti quorum sensing potential of <em>T. chebula</em> Retz. and identification of probable compounds(s) showing anti QS activity and the mechanism of attenuation of <em>P. aeruginosa</em> PAO1 virulence factors.</p> <h3>Methods and Results</h3><p>Methanol extract of <em>T. chebula</em> Retz. fruit showed anti QS activity using <em>Agrobacterium tumefaciens</em> A136. Bioactive fraction (F7), obtained by fractionation of methanol extract using Sephadex LH20, showed significant reduction (p<0.001) in QS regulated production of extracellular virulence factors in <em>P. aeruginosa</em> PAO1. Biofilm formation and alginate were significantly (p<0.05) reduced with enhanced (20%) susceptibility to tobramycin. Real Time PCR of F7 treated <em>P. aeruginosa</em> showed down regulation of autoinducer synthase (<em>lasI</em> and <em>rhlI</em>) and their cognate receptor (<em>lasR</em> and <em>rhlR</em>) genes by 89, 90, 90 and 93%, respectively. Electrospray Ionization Mass Spectrometry also showed 90 and 64% reduction in the production of 3-oxo-C<sub>12</sub>HSL and C<sub>4</sub>HSL after treatment. Decrease in AHLs as one of the mechanisms of quorum quenching by F7 was supported by the reversal of inhibited swarming motility in F7-treated <em>P. aeruginosa</em> PAO1 on addition of C<sub>4</sub>HSL. F7 also showed antagonistic activity against 3-oxo-C<sub>12</sub>HSL-dependent QS in <em>E. coli</em> bioreporter. <em>C. elegans</em> fed on F7-treated <em>P. aeruginosa</em> showed enhanced survival with LT50 increasing from 24 to 72 h. LC-ESI-MS of F7 revealed the presence of ellagic acid derivatives responsible for anti QS activity in <em>T. chebula</em> extract.</p> <h3>Conclusions</h3><p>This is the first report on anti QS activity of <em>T. chebula</em> fruit linked to EADs which down regulate the expression of <em>lasIR</em> and <em>rhlIR</em> genes with concomitant decrease in AHLs in <em>P. aeruginosa</em> PAO1 causing attenuation of its virulence factors and enhanced sensitivity of its biofilm towards tobramycin.</p> </div
