부산대학교 도서관

Chitosan and its oligosaccharides have shown antimicrobial effects against pathogenic bacteria inducing fish diseases. Lactic acid bacterium (LABs) known as probiotics play important roles in the regulation or maintenance of normal flora and pathogenic bacteria. In this study, we investigated the potential of chitosan oligosaccharides (COSs) as natural prebiotics by evaluating their capacities on the growth of both lactic acid bacterium (LAB) and Vibrio anguillarum (V. anguillarum, Listonella anguillarum). First of all, we prepared three COSs (COS1; molecular weight (MW) 1 KDa>, COS2; MW 1~5 KDa, COS3; MW 5~10 KDa) by enzymatic hydrolysis of chitosan and isolated lactobacillus brevis (L. brevis) BK4 from flounder fish intestine. Among the chitosan and its three MW fractions, the two lower MW fractions, COS1 and COS2 markedly decreased pH by increasing the production of organic acids, especially lactic acid in the BK4-cultured mediums. In contrast, the higher MW fraction, COS3 showed no significant difference in pH. Also, COS1 and COS2 significantly increased the growth of BK4 at all the concentrations according to the inoculation times, whereas COS3 and chitosan inhibited them. Furthermore, COS2 showed the strong antibacterial activities as markedly enhancing the inhibitory effect against the growth of V. anguillarum in co-cultured system of BK4 and V. anguillarum compared to that of pure-cultured system. In conclusion, the relatively lower COSs led to the growth of BK4 with the production of lactic acid and improved the anti-bacterial activity against V. anguillarum. This study suggests that the lower MW fractions of COSs can be used as a useful prebiotic candidate to improve fish diseases as the animal feed additives.