Selection of probiotic bacteria and study of their immunostimulatory effect in Penaeus vannamei

The objective of this work was to obtain probiotic bacterial strains with immunostimulatory qualities for shrimp. A total of 80 strains were isolated from the hepatopancreas of healthy wild shrimp (30 +/- 5 g) collected in Manglaralto-Ecuador. The probiotic effect in vitro was evaluated using the agar diffusion technique. Three strains identified as Vibrio P62, Vibrio P63 and Bacillus P64, showed inhibitory effects against Vibrio harveyi (S2). The colonization percentage in shrimp hepatopancreas was analysed using random amplified polymorphic DNA (RAPD) profiles with three primers. The strains P62, P63, and P64 achieved colonization percentages of 83%, 60% and 58%, respectively. The competitive interaction with V harveyi (S2) was evaluated in shrimp using RAPDs and monoclonal antibodies. The inhibition percentage against S2 reached by strains P62, P63 and P64 was 54%, 19% and 34%, respectively. Histopathology was carried out after the colonization and interaction experiments, and confirmed that the probiotic strains had no pathogenic effects on the host. The immunostimulatory effect of P62 and P64 was evaluated in vivo using several immunity tests. Vibrio alginolyticus (Ili) was used as positive control. Shrimp that did not receive any probiotics served as the negative control group, The global immunity index was significantly higher (p < 0.05) in the shrimps stimulated with P64 and V alginolyticus. For the animals stimulated with P62, the immunity index was similar to the control. Mean shrimp weights for three probiotic groups were significantly higher (p <0.05) than the control. In conclusion the isolated strain Bacillus P64 showed both probiotic and immunostimulatory features, while Vibrio P62 only showed good probiotic properties. (C) 2004 Elsevier B.V. All rights reserved.