Abstract
Quorum sensing (QS) is a cell density-dependent regulation of virulent bacterial gene expression by autoinducers that potentially pertains in the epidemic of bacterial virulence. This study was initially designed to evaluate the effect of 5 phenolic compounds in the modulation of QS and virulence factors of Chromobacterium violaceum and Pseudomonas aeruginosa, and to determine the mechanisms of their effects. Biosensor strains were used to assess antibacterial and anti-QS effect of these compounds. Only methyl gallate (MG) among these compounds demonstrated profound anti-QS effect in the preliminary study, and thus only MG was utilized further to evaluate the effects on the synthesis and activity of acyl homoserine lactone (AHL) in C. violaceum and on the modulation of biofilm, motility, proteolytic, elastase, pyocyanin, and rhamnolipid activity in P. aeruginosa. Finally, the effect of MG on the expression of QS-regulated genes of P. aeruginosa was verified. MG suppressed both the synthesis and activity of AHL in C. violaceum. It also restricted the biofilm formation and other QS-associated virulence factor of P. aeruginosa. MG concentration-dependently suppressed the expression of lasI/R, rhlI/R, and pqsA of P. aeruginosa and was non-toxic in in vitro study. This is the first report of the anti-QS mechanism of MG.
Highlights
Quorum sensing (QS) is an inter-cellular communication system of bacteria that is used to collectively control group behaviors[1, 2]
Other compounds with the tested concentrations were not found to be effective enough to interfere in the production of violacein by C. violaceum
Our results indicated that compared to the control which did not contain any drug, the acyl homoserine lactone (AHL)-mediated violacein pigment production in CV026 and its activity were much lower in the presence of methyl gallate (MG) (Supplementary Fig. 3)
Summary
Quorum sensing (QS) is an inter-cellular communication system of bacteria that is used to collectively control group behaviors[1, 2] This process depends on the production, release, and group-wide detection of signal molecules which are known as autoinducers. C. violaceum produces violacein pigment in response to QS regulated gene expression[6] Considering this characteristic, this bacterium is widely used to study the inhibition of acyl homoserine lactone (AHL)-dependent QS by diverse compounds[7,8,9]. The QS signal molecule, AHL has a lactone ring and amide group These phenolic compounds are different than AHL considering their basic structures and their attached functional groups or side chain. Hamamelitannin, a polyphenolic compound with the basic galloyl moiety showed QS inhibitions against S. aureus[31]
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