Anti-quorum quenching activity of methyl gallate isolated from galls of Guiera senegalensis J. F. Gmel (Combretaceae)

Many pathogenic bacteria produce virulence factors controlled by a mechanism of regulation named quorum sensing (QS). Inhibition of bacterial QS system is a more recent therapeutic approach to counterbalance the emergence of multi-drug resistant bacteria. This study aimed to assess the abilities of methanol extract from Guiera senegalensis galls and its isolated compound methyl gallate to quench the quorum sensing system. Methanol extract from galls of G. senegalensis at the concentration of 100 µg/ml demonstrated significant inhibitory effect on pyocyanin and violacein production respectively in Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum CV026. Colum chromatography and recycling High Performance Liquid Chromatography (HPLC) of methanol extract from galls of G. senegalensis led to the isolation of one active quorum quenching compound. Different spectroscopic methods (MS and NMR) were used to elucidate the structure of this isolated compound as being the methyl gallate (MG). Methyl gallate at the final concentration of 12.5 µg/ml demonstrated good anti-QS activity by inhibiting violacein and pyocyanin production. Its low molecular weight and the capacity to interfere with the mechanism of QS make methyl gallate, an interesting candidate for development of drugs as an alternative to antibiotics to combat bacterial resistance.