Damage and recovery of artificial diet rearing silkworms (Bombyx mori L.) exposed to high-concentration florfenicol as well as the dynamic changes of midgut ‌flora after functional bacterium supplementation

Background Florfenicol (FF) is widely used in animal husbandry due to its broad-spectrum bactericidal activity, while there is little research focused on its toxic effects on the silkworm( Bombyx mori L.), a model organism. Result It was demonstrated in this paper that high-concentration florfenicol exposure significantly inhibited the activities of digestive and antioxidant enzymes, reduced the body weight and cocooning ability of silkworms, prolonged the instar duration, and simultaneously led to organelle swelling and vacuolization in the midgut, a large number of autophagosomes, and nuclear condensation. Meanwhile, it was found that exposure to FF reduced the α diversity and richness of the midgut flora, leading to a severe loss of core microbiota. The functional bacterium, Bacillus velezensis LY5, which was demonstrated that it significantly also improved the body weight and cocoon quality of silkworms exposed to FF in this study, accelerated the repair of midgut tissue damage, helped recover the abundance of core midgut flora, increased the proportion of potentially beneficial bacteria, and reduced the excessive proliferation of opportunistic pathogens. Conclusion This study reveals the toxicological mechanism by which high concentrations of antibiotics (FF) disrupt the midgut microbiota balance in silkworms, induce tissue damage, and subsequently impede their growth and development. It also demonstrates for the first time that functional probiotics can effectively reverse this damage by restoring the silkworm midgut microbiota and intestinal tissue