Effects of dietary administration of Bacillus subtilis FPTB13 and
chitin, single or combined, on the systemic immunity, mucosal immunity and resistance of catla (Catla catla) against Edwardsiella tarda
infection were investigated. The probiotic attributes of B. subtilis was tested by conducting antagonism study, safety in catla, in vitro
immunomodulation and dietary
immunomodulation. Results of these studies indicated the probiotic potential of the strain. From the preliminary dietary
immunomodulation study, a dose of 10(9) B. subtilis cells g(-1) was selected for inclusion into diets for subsequent experiments. Experimental diets were prepared by adding B. subtilis (10(9) cells g(-1)),
chitin (2%) and their combination to the basal diet. Different systemic and mucosal immunological parameters viz.
oxygen radical production,
myeloperoxidase content,
lysozyme activity, total
protein content and
alkaline phosphatase activity showed significant enhancement (p<0.05) after 2 weeks of feeding with the combined diet. B. subtilis and
chitin alone also significantly elevated most of the immune responses. All the diets significantly increased the resistance of catla against E. tarda challenge. The highest post-challenge survival was observed in combined group (i.e. 63.33%). In conclusion, B. subtilis and
chitin, alone or combined, had a health ameliorating effect in catla. The results also collectively suggest the usefulness of applying a combined probiotic and
immunostimulant supplemented diet to achieve greater benefits.