In vitro and in vivo potential probiotic activity of Bacillus subtilis and Shewanella algae for use in Litopenaeus vannamei rearing

Shrimp farming intensification has led to problems concerning the use of chlorination and antibiotics. An alternative solution is the use of probiotics to control pathogens. In this regard, the aim of this work was to investigate the antimicrobial activity of three candidate probiotic strains: Bacillus subtilis (IPA-S.51), Shewanella algae (IPA-S.252 and IPA-S.111) isolated from Litopenaeus vannamei against the pathogenic bacteria Vibrio alginolyticus and Vibrio parahaemolyticus. IPA-S.51 and IPA-S.252 were added in the feed and then offered to L. vannamei juveniles during 45 days. A commercial probiotic (CP) was used as a positive control in the first in vitro assay and in vivo experiment. Shrimp hepatopancreas, intestine and feces were collected every week for total heterotrophic bacteria and TCBS quantification. A General Linear Model analysis revealed the probiotic type and pH as the most important variables that influenced candidate inhibitory effect against vibrios. IPA-S.51 produced a greater inhibitory frequency against V. alginolyticus and V. parahaemolyticus. In the in vivo experiment, IPA-S.51 and IPA-S.252 decreased the Vibrio load in the hepatopancreas. It is suggested that this load was shifted to the intestine and ultimately eliminated through feces. Moreover, shrimp fed with IPA-S.51 presented greater final weight, weight gain rate and daily weight gain than the Control and IPA-S.252. Overall, our results showed that B. subtilis strain administration significantly improved shrimp growth and could develop in shrimp hepatopancreas and intestine. Furthermore, feed supplemented with S. algae and B. subtilis strains could also control Vibrio load in the L. vannamei hepatopancreas.