Screening of lactic acid bacteria isolated from fermented food as potential probiotics for aquacultured carp and amberjack

This study aimed to isolate lactic acid bacteria from fermented foods and evaluate their probiotic properties for application to aquaculture. Sixty-five bacteria strains were isolated using MRS (de Man, Rogosa & Sharpe) media. Using a double-layer agar method, three strains, GYP 31, L 15 and K-C2, showed antagonistic activities against all test pathogens belonging to Edwardsiella tarda, Streptococcus dysgalactiae, S. iniae and Lactococcus garvieae. These strains were able to survive in a pH range from 2.0 to 9.0 and at NaCl concentrations of 0, 3 and 5%. In the tolerance test, strain K-C2 displayed higher tolerance than strains GYP 31 and L 15 under the stimulation of acidic pH buffers and artificial gastric-intestinal juices. Thus, strain K-C2 was selected as a probiotic candidate and identified as L. lactis based on the sequences determined in 16S rRNA gene (1438 bp) analysis. It was observed to be ovoid in shape and to be catalase-negative in morphological and biochemical investigations. Strain K-C2 adhered to carp and amberjack intestinal mucus at bacterial densities of 1010 cfu/ml in in vitro tests with adhesion rates of 62 and 58%, respectively. Thus, L. lactis strain K-C2 was considered to be a potential probiotic candidate for use in sustainable aquaculture.