Effects of dietary Bacillus licheniformis on growth performance, intestinal morphology, intestinal microbiome, and disease resistance in common carp (Cyprinus carpio L.)

Abstract

This study was to evaluate the growth, intestinal morphology, intestinal flora, and anti-infection activity against Aeromonas hydrophila in common carp upon adding Bacillus licheniformis to the feed. Four experimental diets supplemented with different concentrations of B. licheniformis were as follows: 0 (CK), 106 colony forming units (CFU)/g (A), 107 CFU/g (B), and 108 CFU/g (C). After 60 days of feeding trial, the fish were intraperitoneally injected with 100 μL of A. hydrophila (LD50=5×106 CFU/mL) every day for a week to measure cytokines. Fish in group C showed the best growth indexes (weight gain rate: 186.88; specific growth rate: 1.76; and feed conversion rate: 1.07). The final body weight, weight gain rate, and specific growth rate in group C were increased by 47.9%, 87.4%, and 53.0%, feed conversion ratio reduced by 42.5%. Fish showed the highest villus height of intestine in group C. The intestinal flora analysis showed that, the richness of phylum, Firmicutes in the treatment groups significantly increased, and that of Bacteroides decreased remarkably. After the infection with A. hydrophila, B. licheniformis at 108 CFU/g significantly upregulated protein levels of pro-inflammatory cytokines (TNF-α, IL-6) and anti-inflammatory cytokines (IL-10, TGF-β) compared with the control group. These results indicated that dietary supplementation of B. licheniformis not only increased the growth and influenced the intestinal development and disease resistance of common carp, but also altered the intestine microbiota structure. Furthermore, in our study, the optimal concentration of B. licheniformis in diets for common carp was equal to 108 CFU/g.