Antibacterial Activities of Metabolites from (American sycamore) against Fish Pathogenic Bacteria.

One approach to the management of common fish diseases in aquaculture is the use of antibiotic-laden feed. However, there are public concerns about the use of antibiotics in agriculture and the potential development of antibiotic resistant bacteria. Therefore, the discovery of other environmentally safe natural compounds as alternatives to antibiotics would benefit the aquaculture industries. Four natural compounds, commonly called platanosides, [kaempferol 3---L-(2,3-di---coumaroyl)rhamnoside (), kaempferol 3---L-(2---coumaroyl-3---coumaroyl)rhamnoside (), kaempferol 3---L-(2---coumaroyl-3---coumaroyl)rhamnoside (), and kaempferol 3---L-(2,3-di---coumaroyl)rhamnoside ()] isolated from the leaves of the American sycamore ) tree were evaluated using a rapid bioassay for their antibacterial activities against common fish pathogenic bacteria including , , , and . The four isomers and a mixture of all four isomers were strongly antibacterial against isolates of and . Against ALM-00-173, and showed the strongest antibacterial activities, with 24-h 50% inhibition concentration (IC) values of 2.13 ± 0.11 and 2.62 ± 0.23 mg/L, respectively. Against LA94-426, had the strongest antibacterial activity, with 24-h IC of 1.87 ± 0.23 mg/L. Neither a mixture of the isomers nor any of the individual isomers were antibacterial against isolates of and at the test concentrations used in the study. Several of the isomers appear promising for the potential management of columnaris disease and streptococcosis in fish.