The In Vitro Activity of a Range of Natural BioflavonoidsAgainst Five Species of Pathogenic Fish Bacteria

The in vitro antibacterial activity of thirty two plant-derived compounds (26 crude herbal extraction and 6 pure citrus-basedbioflavonoids) were tested on five different species of aquatic bacterial pathogens (Aeromonas hydrophila, A. salmonicida, A. sobria,Edwardsiella ictaluri, and E. tarda) over a period of 72 hours at 22 oC. From the agar diffusion test, six pure citrus-based bioflavonoids(apigenin, catechin, hesperidin, morin, naringin and quercetin) appeared to impact on growth when used at concentrations ranging from 10ppm - 1000 ppm. To confirm their effect on the growth dynamics of each bacteria, a 1000 ppm dose of the appropriate bioflavonoid wasadded to a bacterial culture and daily changes in culture growth were measured. Quercetin was found to be bacteriocidal against all thebacterial strains. Morin was found to be bacteriocidal against only 4 out of 6 strains while hesperidin was found to affect the growth of allthe tested bacterial strains, working both as a bacteriocidal and as a bacteriostatic agent. Apigenin performed poorly and had no effect onthe growth of any bacterial strain while catechin and naringin were found to be generally bacteriostatic in action but had little impact onthe growth of the Aeromonad strains. From the current in vitro work, it was concluded that certain plant extracts do have an impact on thegrowth dynamics of select bacteria and show potential as alternatives to the use of antimicrobials, but further research is required to assesstheir performance in vivo.