Modulation of Quorum Sensing and Pyocyanin in Pseudomonas aeruginosa

Abstract

Antibiotic resistant Pseudomonas aeruginosa is one of the primary causes of hospital-acquired infections and accounts for the deaths of thousands of immuno-compromised patients each year. The bacteria use quorum sensing (QS) to regulate expression of virulence factors based on cell density. The antagonism of the LasI/LasR and RhlI/RhlR QS circuits in P. aeruginosa should disrupt downstream virulence and circumvent antibiotic resistance. From high-throughput screening of small molecules, an active compound was identified that significantly reduces pyocyanin production. Based on this hit, a series of highly effective hybrid analogues was rationally designed and synthesized. While LasR and RhlR were the original QS targets of these antagonists, recent microarray results suggest that these compounds bind to other proteins involved in oxidative stress response to eliminate pyocyanin production. A diazirine-based photoaffinity label (PAL) was designed based on the most potent pyocyanin inhibitors and successfully synthesized. Tandem mass spectrometry analyses of PAL photo-crosslinking experiments with P. aeruginosa in vivo implicate polymyxin-resistance protein ArnA and PA5441 as the primary targets of the pyocyanin inhibitors. Preliminary antibiotic studies demonstrate that these inhibitors lower the minimal inhibitory concentrations of polymyxin B.