AEM Accepts, published online ahead of print on 23 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01059-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of catechin as one of the flavonoids from Combretum albiflorum bark extract reducing the production of quorum-sensing controlled virulence factors in Pseudomonas aeruginosa PAO1

Olivier M. Vandeputte^*, Martin Kiendrebeogo, Sanda Rajaonson, Billo Diallo, Adeline Mol, Mondher El Jaziri, and Marie Baucher

Plant Biotechnology Unit, BioVallée, rue Adrienne Bolland 8, B-6041 Gosselies, Belgium; Laboratoire de Biotechnologie Végétale, Université Libre de Bruxelles, rue Adrienne Bolland 8, B-6041 Gosselies, Belgium; Laboratoire de Biochimie et de Chimie Appliquées, Université de Ouagadougou, 09 BP 848 Ouagadougou 09, Burkina Faso; Laboratoire de Physiologie Végétale, Université d'Antananarivo, B.P. 906 Antananarivo 101, Madagascar

^* To whom correspondence should be addressed. Email: ovdeputt{at}ulb.ac.be.

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 HPLC profiles and the MS spectra obtained for a catechin standard and for the active C. albiflorum fraction. Besides, standard catechin had a significant negative effect on pyocyanin and elastase productions, 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 RhlR- and 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.