Combined effect of gallic acid and catechin against Escherichia coli

The antimicrobial effect of gallic acid and catechin on Escherichia coli cultures was investigated. The antimicrobial activity was evaluated by measuring the absorbance of liquid culture media at 600 nm, by an agar-well diffusion method and by scoring colony forming units. Then, the OD600 and CFU/mL values decreased when the medium was supplemented with gallic. Besides, the CFU/mL values decreased continuously with the time of exposure to gallic acid in a range of 360 min. Likewise, the diameters of the growth inhibition zones around the wells increased gradually with the content of gallic acid or catechin. In summary, both polyphenols displayed growth inhibitory effects on the bacterium. Further, the antibacterial effects were dependent on dose, time of exposure and type of polyphenol. Gallic acid showed a higher anti-E. coli effect compared to catechin. Mixtures of subeffective doses of gallic acid and an effective dose of catechin produced growth inhibition halos similar to those produced by catechin alone. (C) 2014 Elsevier Ltd. All rights reserved.