Antimicrobial property of gallic acid from Terminalia chebula Retz. effects on two pathogenic Aeromonas species isolated from cultured eel

Abstract

_Aeromonas spp._ are prevalent pathogens in farmed eel, which induce highly infectious diseases, such as hemorrhagic septicemia and gill-rot disease. Research on the application of ethanol and water extracts from traditional Chinese herbs in controlling the diseases has increased. However, the exact antibacterial components in majority of these herbs were not well-studied. Four fractions or components were isolated from _Terminalia chebula_ Retz. ethanol extract in our previous study. In the present study, their antibacterial effects on _A. hydrophila_ and _A. veronii_ were assessed using microcalorimetry. The results showed that component III (a single chemical constituent, gallic acid) had the strongest antibacterial effect compared with three other fractions. The inhibitory effect was enhanced as the concentration of component III increased, and the minimum inhibitory concentrations of component III to _A. hydrophila_ and _A. veronii_ were found to be 0.56 mg/ml and 0.74 mg/ml respectively. This is the first study in which the antibacterial component of _T. chebula_ extract on aquatic bacteria growth was screened and determined by microcalorimetry.