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.