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Antimicrobial Activity of 4-O-methylgallic Acid Isolated from Phyllanthus polyphyllus L. against Foodborne Pathogenic Bacteria and Yeasts

Abstract The aim of this study was to evaluate the antimicrobial activity of 4-O-methylgallic acid isolated from Phyllanthus polyphyllus L. and examine its possible antimicrobial mode of action against food-borne pathogenic bacteria and yeast. The bioassay-guided fractionation of methanol extract of leaves led to the isolation of active compound 4-O-methylgallic acid (4-O-MGA). The antimicrobial activity were assessed against two Gram-positive (Staphylococcus aureus and Streptococcus faecalis), five Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris and Salmonella typhimurium) bacteria and two yeasts (Candida albicans and Cryptococcus neoformans) using disk diffusion method followed by a standardized microdilution assay. 4-O-MGA exhibited antimicrobial activity against all tested bacteria with MIC ≥ 0.125 mg/mL and MBC ≥ 0.25 mg/mL. Among tested organisms, Gram-positive bacteria were more sensitive than Gram-negative, and yeasts showed more resistance with higher MIC 1.0 mg/mL and MFC ≥ 2.0 mg/mL. Much effort was focused on elucidating the mechanism of antimicrobial action of 4-O-MGA against S. aureus and E. coli by observing the changes in membrane integrity as confirmed by release of loss of 260 nm absorbing materials and leakage of potassium with outer membrane permeability, and against a yeast C. albicans as confirmed by inhibitory effects on biofilm formation and sterol content in the plasma membrane. The antimicrobial properties of 4-O-MGA suggest that, also considering its antioxidant and well known nutritional functions, it has potential for development as an antimicrobial agent for control of food-related pathogenic microbes.