In Vitro Antibacterial and Synergistic Effect of Chitosan-Phytochemical Conjugates Against Antibiotic Resistant Fish Pathogenic Bacteria.

Chitosan-phytochemical conjugates exhibited significant antibacterial effect with minimum inhibitory concentration (MIC) ranging from 128 to 2048 µg/ml against antibiotic-resistant fish pathogenic bacteria such as Edwardseilla tarda , Vibrio harveyi and Photobacterium damselae which were isolated from Korean cultured fish. Furthermore, the MIC values of old-fashioned antibiotics such as erythromycin and oxytertacycline drastically reduced in combination with chitosan-phytochemical conjugates against the fish pathogenic bacteria. The combination of conjugates with erythromycin and oxytetracycline gave median ∑FIC results ranging from 0.281 to 0.625 and 0.312 to 0.625, respectively. This result indicates the synergistic antibacterial effects and an increased susceptibility against the antibiotics.