Evaluation of the probiotic potential of a competitive exclusion culture from 2 tilapia (Oreochromis niloticus) intestinal microbiota

Abstract

409 Stress conditions in intensive aquaculture are generating serious economic loss due to 410 disease outbreaks. For that reason, antibiotics have been used to reduce infection, increase 411 growth rates or even prevent diseases; nevertheless, the application of repeated doses or low 412 concentrations of antibiotics increases the risk of the apparition of antibiotic-resistant bacteria, 413 creating thus the need for alternative biotechnological methods such as probiotic bacteria. 414 Additionally, previous research suggests that bacteria consortia and autochthonous bacteria 415 improve fish health with benefits beyond antibiotics application. These reasons are why this 416 project proposed to determine the probiotic potential of a continuous-flow competitive 417 exclusion culture developed from intestinal microbiota collected from tilapia (O. niloticus) 418 intestinal content, the major cultured fish species in Colombia. The project was divided into 419 three phases; The first phase involved establishing a competitive exclusion culture with 420 antibacterial activity against S. agalactiae. From the last, it was possible to identify that after 421 33 days of incubation of the CFCEC, the more abundant bacteria were from the phyla 422 firmicutes, Lactococcus being the most abundant genus, showing the displacement of 423 opportunistic pathogenic bacteria. The second stage included the in vitro characterization of 424 bacteria isolated from a competitive exclusion culture to identify the probiotic potential; also, a 425 probiotic mixture was designed, incorporated into fish feed, and stabilized in a vacuum package 426 at 4°C. From that, three bacteria were isolated and identified: Lactococcus lactis A12, Priestia 427 megaterium M4, and Priestia sp. M10, a mixture design of the three bacteria, was established 428 for in vivo use. The third phase was the in vivo validation of the fish production.