In vitro evaluation of the probiotic candidates isolated from the gut of Clarias gariepinus with special reference to the in vivo assessment of live and heat-inactivated Leuconostoc mesenteroides and Edwardsiella sp.

Fish gut microbiota contains many potential probiotics that can be used in aquaculture. The aim of this study was to isolate beneficial probiotic bacteria from the gut of African catfish, Clarias gariepinus, and to evaluate the most suitable in vivo probiotic candidates. Eighty-nine gut bacterial isolates were screened for in vitro antibacterial activities against five common isolated fish pathogens, Aeromonas sobria, A. hydrophila, Pseudomonas aeruginosa, P. putida, and Staphylococcus aureus. Results found that nine out of 89 isolates had antibacterial activities with at least one pathogen. Two out of nine isolates demonstrated pathogenic effects following intraperitoneal injection. The remaining non-pathogenic seven strains were able to survive in high bile concentration (10%) and at different acidic pH values. Three out of seven strains were sensitive to all selected antibiotics. Four out of seven strains had amylase and protease activities. Based on 16S rRNA gene analysis, the isolated strains were identified as follows: Bacillus subtilis (6HN), B. amyloliquefaciens (7HN), B. cereus (29HN), Leuconostoc mesenteroides (13HN), Edwardsiella sp. (34HN), and Citrobacter freundii (24HN and 31HN). Comparative in vivo study of dietary supplementations of heat-inactivated and live L. mesenteroides (13HN) and Edwardsiella sp. (34HN) showed better improvements in growth, immunity, and the expression of myostatin (MSTN) and pituitary adenylate cyclase-activating polypeptide (PACAP) in the spleen of C. gariepinus of heat-inactivated probiotics than live one.