The probiotic effects, dose, and duration of lactic acid bacteria on disease resistance in Litopenaeus vannamei

Four lactic acid bacteria with a high capacity for acid production were screened from 113 lactic acid bacteria (LAB) isolated from aquaculture systems, and were identified as Lactococcus lactis (S1 and S2), Enterococcus faecali (F3 and F7) by 16S rDNA sequencing. These four candidates exhibited favorable probiotic properties, including no haemolytic activity, good auto-aggregation performance, tolerance to simulated gastric fluid, and antagonistic activity against pathogens. To determine the ideal probiotic feeding dose and duration that would maximize protection against pathogens, L. vannamei were fed a probiotic supplemented diet at a series of concentrations for up to 60 days, and then challenged with Vibrio harveyi every 15 days. In vivo studies demonstrated that supplementation with L. lactis (S1 and S2) and E. faecalis (F3 and F7) significantly improved growth performance and feed utilization in the probiotic-treated groups compared to the control group. The findings suggested that administration of F7 and S2 strains at 106 CFU g−1 for 30–45 d was more effective at suppressing V. harveyi infection than any of the other feeding regimens. This study establishes a theoretical foundation for the practical use of probiotics.