Mechanism of Ligilactobacillus salivarius GX118 in Regulating the Growth of Rainbow Trout (Oncorhynchus mykiss) and Resistance to Aeromonas salmonicida Infection

Lactic acid bacteriaLigilactobacillus salivariushas been shown to be a substitute for antibiotics in the treatment of bacterial disease in high animals. However, its beneficial mechanism in fish farming is still unclear. This study evaluated the antagonistic effects of theLigilactobacillus salivariusGX118 strain onAeromonas salmonicidaand its regulation of rainbow trout growth in vivo and in vitro. The results found that GX118 produces an antibacterial substance that can directly destroy the cell wall ofA. salmonicida. Whole-genome sequencing of GX118 revealed that Enterolysin A is a type III bacteriocin with antibacterial properties. An in vivo experiment showed that the supplementation of GX118 in diet competitively inhibited the colonization ofA. salmonicidain the intestine. In addition, it was able to improve the growth performance of rainbow trout within a 21-day feeding experiment. The supplementation of GX118 increased the diversity of gut microbiota, in which the abundance ofBacteroidota,Blautia, andRhodobacteraceaeincreased. In addition, the use of GX118 activated the expression ofIFN-γandNF-κBgenes and reduced the expression level ofIL-6andIL-8, thus exhibiting a certain effect on activating the immunity of rainbow trout. This study provides a scientific basis for the development of antibacterial probiotics in the healthy farming of rainbow trout.