Use of Direct-Fed Microbes To Enhance Shrimp Resistance to a Vibrio Parahaemolyticus Strain Causing Early Mortality Syndrome
Early Mortality Syndrome (EMS) is a widespread bacterial infection of shrimp, attributed to pathogenic Vibrio parahaemolyticus strains (VP-EMS). This disease threatens aquaculture production and global food security. A valuable and alternative approach to using antibiotics for pathogen control, is the practice of incorporating direct-fed microbes (DFM) or probiotics. In order to evaluate the hypothesis that probiotics (specific strains of Bacillus subtilis spores) are able to provide shrimp, Litopenaeus vannamei, protection to the EMS disease, a pathogen growth model, disease challenge model, and probiotic feed coating methodologies were developed and refined, allowing independent shrimp probiotic trials to be piloted.
A single probiotic strain of Bacillus subtilis: O14VRQ and a blend of Bacillus subtilis strains: Plus10, were evaluated as feed additives or as water additions, for their efficacy. Accordingly, two independent trials were conducted in which shrimp were fed daily with a probiotic-coated feed for seven days, before a challenge with VP-EMS. Each trial consisted of a negative control (no VP-EMS exposure, no probiotic) and positive control (VP-EMS exposure, no probiotic), with five additional probiotic treatment groups, which were fed and exposed to VP-EMS in the same manner as the positive control. Shrimp were observed for clinical signs of disease after the initial exposure and were continuously exposed every 24 hours until 50% of the population remained in the positive control treatment. Both probiotics studied were shown to significantly (p < 0.05) improve shrimp survival. Overall the data presented in this work demonstrates that probiotic prophylaxis is reliant upon probiotic dose, regardless of application.