Effects of probiotics ( Bacillus coagulans ) supplementation after antibiotic administration on growth, immunity, and intestinal microflora in turbot Scophthalmus maximus

To evaluate the effects of probiotics following the administration of different antibiotics on turbot Scophthalmus maximus , a 35-day culture experiment with dietary feeding with antibiotics and probiotics was conducted. Groups E and F received enrofloxacin and florfenicol for 15 days respectively, followed by supplementation of probiotics B. coagulans for 20 days. Fish growth, immunity, antibiotic resistance genes (ARGs), and intestinal microflora were investigated. Significant growth was observed, and the expression of IL-8 and TNF-α was significantly upregulated in most of examined organs in both groups, indicating B. coagulans supplementation improves the growth performance. The four analyzed ARGs were downregulated with B. coagulans supplementation though they were upregulated with antibiotic administration. The administration of florfenicol decreased Vibrio abundance but increased the abundance of potentially pathogenic bacteria such as Clostridia , Turicibacter , and Erysipelotrichia , and the administration of enrofloxacin increased the abundance of Clostridia . Notably, B. coagulans supplementation decreased the abundance of opportunistic pathogens such as Clostridia , Turicibacter , Erysipelotrichales , and Lachnospiraceae , indicating B. coagulans may help restore homeostasis of intestinal microflora. Overall, the present study results revealed the probiotic B. coagulans yields a beneficial effect on juvenile turbot and provides a novel therapeutic approach to reduce negative effects caused by antibiotics in fish.