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The objective of the present study was to characterize lactobacilli isolates from the feces of male Wistar rats. Various physiological features of the candidate probiotic isolates were preliminarily investigated, including tolerance to simulated gastric juice and bile salts, antimicrobial activity, antibiotic susceptibility and in vitro aggregation. Based on their morphological and biochemical characteristics, four potential probiotic isolates (CS2, CS3, CS4, and CS7) were screened. The isolates showed good tolerance to stimulated gastric juice and bile salts. CS4 and CS7 exhibited strong antibacterial activities against the pathogens tested as assessed in neutral pH culture supernatants. All lactobacilli isolates were susceptible to all the tested antibiotics, except vancomycin. Moreover, the isolate CS4 and CS7 were found to possess stronger cell surface traits such as hydrophobicity, auto-aggregation and co-aggregation capacity. In addition, CS4 and CS7 had greater b-galactosidase activities than the others. Biochemical tests and 16S rRNA gene sequencing confirmed that CS2, CS3, CS4 and CS7 are Lactobacillus intestinalis PJ2, L. sakei PJ3, L. helveticus PJ4, and L. plantarum PJ7, respectively. Based on the obtained results, L. helveticus PJ4 and L. plantarum PJ7 are ideal in vitro probiotic candidates and require further in vivo evaluation.

Labeo rohita fingerlings were fed for 60 days with basal diet (BD) or one of the following experimental diets: DI (BD + B. subtilis); DII (BD + B. subtilis + L. plantarum); DIII (BD + B. subtilis + P. aeruginosa) and DIV (BD + B. subtilis + P. aeruginosa + L. plantarum). Various growth and immune parameters were examined at 30 and 60 days postfeeding. The fish group fed DIV diet had better improvement (P < 0.05) in weight gain, specific growth rate (SGR) and feed conversion ratio (FCR) than the control and other treatment groups. The serum lysozyme activities, alternative complement pathway activity, phagocytic activity and respiratory burst activity in head kidney macrophages of L. rohita increased significantly in the experimental groups throughout the trial period. Superoxide dismutase increased significantly in the experimental groups, except DI fed group, after 60 days of feeding. A significant improvement in serum IgM level was observed in the treatment groups at 30 days of feeding only. Further, fish fed the DIV diet had highest (P < 0.05) postchallenge survival rate (86.6%), followed by DII (73.3%) and DIII (66.6%) against A. hydrophila infection. Considering these promising results, we suggest that a multi‐species probiotic supplementation in equal proportions for 60 days can effectively improve growth and immunity of L. rohita.