Isolation, characterization and mode of antimicrobial action against V ibrio cholerae of methyl gallate isolated from A cacia farnesiana

Aims The antimicrobial activity of A cacia farnesiana against V ibrio cholerae has been demonstrated; however, no information regarding its active compound or its mechanism of action has been documented. Methods and Results The active compound was isolated from A . farnesiana by bioassay‐guided fractionation and identified as methyl gallate by nuclear magnetic resonance ( NMR ) techniques ( 1 H NMR and 13 C NMR ). The minimum bactericidal concentration ( MBC ) of methyl gallate and its effect on membrane integrity, cytoplasmic pH, membrane potential, ATP synthesis and gene expression of cholera toxin ( ctx ) from V . cholerae were determined. The MBC of methyl gallate ranged from 30 ± 1 to 50 ± 1 μg ml −1 . Methyl gallate affected cell membrane integrity, causing a decrease in cytoplasmic pH (pH in , from 7·3 to <3·0), and membrane hyperpolarization, and ATP was no longer produced by the treated cells. However, methyl gallate did not affect ctx gene expression. Conclusions Methyl gallate is a major antimicrobial compound from A . farnesiana that disturbs the membrane activity of V . cholerae . Significance and Impact of the Study The effects of methyl gallate validate several traditional antimicrobial uses of A . farnesiana , and it is an attractive alternative to control V . cholerae .