Growth Inhibition of Selected Aquatic Bacteria by Tannic Acid and Related Compounds

Abstract Tannic acid, propyl gallate, methyl gallate, and gallic acid were tested for their inhibitory effects on selected aquatic microorganisms by the well assay technique. Tannic acid, propyl gallate, and methyl gallate in deionized water inhibited the growth of Aeromonas hydrophila, A. sobria, Edwardsiella iclaluri, E. tarda, Pseudomonas fluorescens, and Escherichia coli, but gallic acid did not. When 500-μg/mL concentrations of these four compounds were tested in sterilized fish pond water at pH 7.0 and with a low bacterial inoculum of 103–104 colony-forming units (CFU) per milliliter, they inhibited the growth of P. fluorescens and (except for tannic acid) E. coli. Pseudomonas fluorescens inoculated at 103–104 CFU/mL in pond water was inhibited by methyl gallate, propyl gallate, and tannic acid concentrations as low as 50 μg/mL, but a gallic acid contration of 100 μg/mL was required for inhibition. Escherichia coli was inhibited by methyl gallate and propyl gallate at 250 μg/mL and by gallic acid at...