Integrated application of two different screening strategies to select potential probiotics from the gut of channel catfish Ictalurus punctatus

In this study, 342 bacterial strains were isolated from the gut of channel catfish Ictalurus punctatus. Two different screening strategies, including the production of antagonistic effects against pathogens and the capacity of secreting exoenzyme, were used to select potential probiotics from the bacterial strains. Among them, 6 isolates showed antagonism against the pathogens, 15 isolates could produce high amylase and protease, and 3 isolates (BHI344, BH0142 and BH03124) had both the two characteristics. Then, BHI344, BH0142, and BH03124 were tested for survival rate in channel catfish bile and at low pH, antimicrobial susceptibilities, and pathogenicity in channel catfish. The results of the obtained assays showed that BHI344 possessed the broadest inhibitory potential, a strong ability of secreting extra-cellular amylase and protease, high viability in simulated gastrointestinal conditions, and sensitivity to most of the used antibiotics and non-pathogenic to channel catfish. Therefore, it could be selected as the most promising probiotics candidate. BHI344 was identified as Bacillus subtilis based on the phenotypic characterization and 16S rRNA gene sequencing.