Effects of potential probiotic Bacillus subtilis KADR1 and its subcellular components on immune responses and disease resistance in Labeo rohita

The present study was conducted to determine the effects of Bacillus subtilisKADR1 and its subcellular components on immunity and disease resistance in Labeo rohita against Aeromonas hydrophila infection. Fish were fed diet containing different concentrations of live bacterial cells (DI-10(6), DII-10(8) and DIII-10(10) CFU/g) and another group of fish were immunized intraperitoneally with cellular components (WCPs, CWPs and ECPs) of Bacillus subtilisKADR1. After 4weeks of trial, fish were challenged intraperitoneally with Aeromonas hydrophila cell suspension and survival percentage was recorded. Significantly higher post-challenge survivability was recorded in fish groups fed 10(8) CFU/g of KADR1 (80.24%; RPS=75.76%) or immunized with WCPs (77.77%; RPS=72.73%), compared with the control (18.51%). Analysis of immunological parameters viz. serum lysozyme, phagocytosis, serum total protein, respiratory burst, serum IgM levels, superoxide dismutase and alternative complement pathway activity reflected significant enhancement (p<.05) of immune response in fish fed 10(6), 10(8) and 10(10) CFU/g of live cells, or immunized with cellular components of Bacillus subtilisKADR1, with the highest values were observed DII fed group, followed by the group immunized with WCPs. Our results suggest that dietary administration of Bacillus subtilisKADR1 at 10(8) CFU/g can effectively enhance the immune responses and disease resistance in Labeo rohita against Aeromonas hydrophila.