Effect of dietary supplementation with Leuconostoc mesenteroides DH on the antimicrobial capacity and overall health of juvenile loach (Misgurnus anguillicaudatus)

Misgurnus anguillicaudatus (loach) is one of the most economically advantageous aquaculture species in Asia. However, the expansion of intensive farming has increased the incidence of fish disease. Among various solutions, the use of probiotics is the best strategy for dealing with the threat of pathogens in aquaculture, while promoting the overall development of fish. Consequently, this study systematically investigated the specific roles of Leuconostoc mesenteroides DH (DH strains) in aquaculture from the four aspects of probiotics (secretion of antibacterial substances; competitive exclusion of adhesion sites; immune system regulation; and enhancement of intestinal barrier function), which are beneficial for hosting antibacterial capacities. In vitro experiments revealed that the DH strains had antibacterial effects on eight common pathogens in aquaculture, and significantly inhibited the growth, protease production and biofilm formation of Aeromonas hydrophila (A. hydrophila). Simultaneously, the DH strains could adhere to the intestinal tract, which competitively prevented the adhesion of A. hydrophila to the intestinal mucus of the loach. The dietary supplementation of DH strains for 56 d significantly improved the digestive enzyme activities and growth performance of juvenile loaches. For the infection attack test with A. hydrophila, erythrocyte phagocytosis in juvenile loach was significantly enhanced, whereas the apoptosis of hemocytes was hindered after feeding with the DH strains. Concurrently, the level of damage in the intestinal tracts of juvenile loaches was reduced, and the concentrations of intestinal permeability-related factors (D-lactic acid and diamine oxidase) in the plasma were remarkably decreased, and the survival rates were significantly improved. These results indicated that the DH strains enhanced the abilities of the hosts to combat pathogens in many ways and improved their overall health, which established a theoretical foundation to promote the sustainable development of the aquaculture industry.