Effect of cellular products of potential probiotic bacteria on the immune response of Labeo rohita and susceptibility to Aeromonas hydrophila infection

In the present study, the immunological efficacy of cellular components from the potential probiotic bacteria Bacillus subtilis VSG1, Pseudomonas aeruginosa VSG2, and Lactobacillus plantarum VSG3 was evaluated in Labeo rohita fingerlings. Fish were immunized intraperitoneally with 0.1 mL phosphate-buffer solution (PBS) containing 0.1 mg of any of the following cellular components: intercellular products (ICPs) of VSG1 (BS-ICPs), heat-killed whole cell products of VSG2 (PA-HKWCPs), or ICPs of VSG3 (LP-ICPs). Fish injected with 0.1 mL PBS served as the control. Various immunological parameters, including the expression of immune-related genes, were measured 14 and 21 days post-immunization. The fish were challenged with Aeromonas hydrophila and mortality was recorded up to 21 days post-infection. The results revealed that administration of cellular components significantly increased the activity of serum lysozyme and the alternative complement pathway, phagocytosis, and respiratory bursts throughout the experimental period. Total serum protein, albumin, and globulin levels were significantly higher in experimental groups than in the control up to 14 days post-immunization, and decreased thereafter. With respect to immune-related genes, IL-1β, COX-2, iNOS, and IL-10 were highly (P