Identification of Catechin as One of the Flavonoids from Combretum albiflorum Bark Extract That Reduces the Production of Quorum-Sensing-Controlled Virulence Factors in Pseudomonas aeruginosa PAO1

Abstract

Quorum-sensing (QS) regulates the production of key virulence factors in Pseudomonas aeruginosa and other important pathogenic bacteria. In this report, extracts of leaves and bark of Combretum albiflorum (Tul.) Jongkind (Combretaceae) were found to quench the production of QS-dependent factors in P. aeruginosa PAO1. Chromatographic fractionation of the crude active extract generated several active fractions containing flavonoids, as shown by their typical spectral features. Purification and structural characterization of one of the active compounds led to the identification of the flavan-3-ol catechin [(2R,3S)-2-(3,4-dihydroxyphenyl)-3,4-dihydro-1(2H)-benzopyran-3,5,7-triol]. The identity of catechin as one of the active molecules was confirmed by comparing the high-pressure liquid chromatography profiles and the mass spectrometry spectra obtained for a catechin standard and for the active C. albiflorum fraction. Moreover, standard catechin had a significant negative effect on pyocyanin and elastase productions and biofilm formation, as well as on the expression of the QS-regulated genes lasB and rhlA and of the key QS regulatory genes lasI, lasR, rhlI, and rhlR. The use of RhlRand LasR-based biosensors indicated that catechin might interfere with the perception of the QS signal N-butanoyl-L-homoserine lactone by RhlR, thereby leading to a reduction of the production of QS factors. Hence, catechin, along with other flavonoids produced by higher plants, might constitute a first line of defense against pathogenic attacks by affecting QS mechanisms and thereby virulence factor production.Pseudomonas aeruginosa is a gram-negative bacterium infecting insects, plants, animals, and humans (65). As an opportunistic pathogen, P. aeruginosa is a major cause of nosocomial diseases and mortality in immunocompromised patients and particularly in patients with cystic fibrosis, diffused panbronchitis, and pulmonary deficiencies (21, 54). Successful infection of diverse hosts is due to the profusion and diversity of virulence factors secreted by P. aeruginosa such as proteases, exopolysaccharides and redox-active compounds, as well as to its capacity to form biofilms (9, 60, 62).Many pathogenic bacteria trigger the production of their virulence factors in a population density-dependent manner, a cell-to-cell communication mechanism known as quorum sensing (QS) (24). This mechanism enables bacteria to detect their population density through the production, release, and perception of small diffusible molecules called autoinducers and to coordinate gene expression accordingly (7,9,13,24,84). In P. aeruginosa, two QS systems (las and rhl) drive the production (by the synthetases LasI and RhlI) and the perception (by the transcription factors LasR and RhlR) of the acyl-homoserine lactones (AHL) N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL), respectively (9, 62). Once LasR interacts with 3-oxo-C12-HSL, it induces the las system (by increasing lasI expression) and triggers the p...

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…Separately, in studies of 50 medicinal plants from South Florida, six plants representing five different families were found to have QSI activity against C. violaceum and A. tumefaciens and could inhibit production of elastase, pyoverdin, and biofilms of P. aeruginosa (277,278). Several flavenoid-like compounds were found to be produced by one of these species, a member of the Combretum family, and the molecule catachin (a flavan-3-ol) was one compound isolated that accounted for these activities (136).…”

Quorum sensing in bacterial virulence

“…These molecules specifically inhibited the activation of virulence genes by quorum sensing, reduced biofilm tolerance to tobramycin and also decreased virulence in a Caenorhabditis elegans pathogenesis model. In a recent study, a screening of quorum-sensing-inhibiting molecules derived from the plant species Combretum albiflorum revealed that catechin has a negative impact on the production of quorumsensing-dependent virulence factors (Vandeputte et al, 2010). Subinhibitory concentrations of macrolides have been shown to be effective in inhibiting quorum-sensingdependent virulence both in vivo and in vitro (Imamura et al, 2004;Molinari et al, 1993;Sofer et al, 1999;Tateda et al, 2001).…”

Identification of a Pseudomonas sp. that Inhibits RHL System of Quorum Sensing

“…Reversed-phase HPLC analysis revealed a major peak (96.673 %) (Fig. 5) detected by its absorbance at 254 nm [15]. This major peak, designated Peak 3, was subjected to further analysis.…”