Influence of probiotic and prebiotic supplementation on intestinal microbiota and resistance to Edwardsiella ictaluri infection in channel catfish (Ictalurus punctatus) following florfenicol administration

Enteric septicemia of catfish (ESC), caused by the gram-negative enteric bacteria Edwardsiella ictaluri, is a significant threat to catfish aquaculture in the southeastern United States. Antibiotic intervention can reduce mortality; however, antibiotic use results in an imbalance, or dysbiosis, of the gut microbiota, which may increase susceptibility of otherwise healthy fish to enteric infections. Herein, recovery of the intestinal microbiota and survivability of channel catfish in response to ESC challenge was evaluated following a 10-day course of florfenicol and subsequent probiotic or prebiotic supplementation. Following completion of florfenicol therapy, fish were transitioned to a basal diet or diets supplemented with a probiotic or prebiotic for the remainder of the study. Digesta was collected on Days 0, 4, 8 and 12, beginning on the first day after cessation of antibiotic treatment, and gut microbiota was characterized by Illumina sequencing of the 16S rRNA gene (V4 region). Remaining fish were challenged with E. ictaluri and monitored for 32 days post-challenge. Florfenicol administration resulted in dysbiosis characterized by inflated microbial diversity, which began to recover in terms of diversity and composition 4 days after cessation of florfenicol administration. Fish fed the probiotic diet had higher survival in response to ESC challenge than the prebiotic (p = .019) and negative control (p = .029) groups.