Establishment and characterization of a competitive exclusion bacterial culture derived from Nile tilapia (Oreochromis niloticus) gut microbiomes showing antibacterial activity against pathogenic Streptococcus agalactiae

Authors: MELO-BOLÍVAR, JAVIER - Universidad De La Sabana; RUIZ-PARDO, RUTH - Universidad De La Sabana; Hume, Michael; Nisbet, David; RODRÍGUEZ-VILLAMIZAR, FERNANDO - Corpoica; ALZATE, JUAN - University Of Antioquia; JUNCA, HOWARD - Microbiomas Foundation; VILLAMIL-DIAZ, LUISA - Universidad De La Sabana

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2019
Publication Date: 5/3/2019
Citation: Melo-Bolívar, J.F., Ruiz-Pardo, R.Y., Hume, M.E., Nisbet, D.J., Rodríguez-Villamizar, F., Alzate, J.F., Junca, H., Villamil-Diaz, L.M. 2019. Establishment and characterization of a competitive exclusion bacterial culture derived from Nile tilapia (Oreochromis niloticus) gut microbiomes showing antibacterial activity against pathogenic Streptococcus agalactiae. PLoS One. 14(5):e0215375. https://doi.org/10.1371/journal.pone.0215375.
DOI: https://doi.org/10.1371/journal.pone.0215375

Interpretive Summary: This study reports the characterization of a tilapia fish-derived intestinal bacterial culture (CEC) with the potential to combat tilapia bacterial pathogens and to improve tilapia production as a food source. The CEC was developed from adult tilapia and samples were collected over two months. The pH varied from 6.25 to 6.35 throughout culturing, while bacterial cell counts stabilized at day 9 and were maintained to day 68. The main bacteria species changed over time, with Cetobacterium being the most abundant in the first two days, but, by day 33, a Lactococcus species emerged as the most abundant. This predominance of Cetobacterium was accompanied by the highest level of killing effectiveness in assays against the tilapia pathogen Streptococcus agalactiae. This antimicrobial activity disappeared by day 3 and as the Cetobacterium decreased in numbers. The study demonstrated the application of CEC technology to develop a tilapia culture with antimicrobial activity against a tilapia pathogen. These results are of interest to aquaculture researchers and producers seeking alternatives to traditional antibiotics to treat disease and improve production in aquaculture settings.

Technical Abstract: This study reports the characterization of the microbial community composition, establishment, and dynamics on a continuous-flow competitive exclusion culture (CFCEC) derived from gut microbiomes of Nile tilapia (Oreochromis niloticus) specimens from aquaculture farms in Colombia. 16S rRNA gene amplicon Illumina sequencing was used to identify taxonomical changes in the CFCEC microbial community over time. The CFCEC was developed from adult tilapia from two farms in Colombia, and CFCEC samples were collected over two months. The pH varied from 6.25 to 6.35 throughout culturing, while anaerobic and aerobic cell counts stabilized at day 9, at 10**9 CFU mL**-1, and were maintained to day 68. A variation in the CFCEC bacterial composition was observed over time. Cetobacterium was the most abundant in the first two days and coincided with a higher CFCEC supernatant antimicrobial effect against the fish pathogen Streptococcus agalactiae. Antimicrobial activity against S. agalactiae disappeared by day 3. Changes in bacterial composition continued to day 33, with Lactococcus spp. becoming the most abundant member of the community. In conclusion, the study of the CFCEC from intestinal tract of Nile tilapia (Oreochromis niloticus) by 16S rRNA gene sequencing allowed identification of predominant bacterial genera in the continuous-flow competitive exclusion culture exhibiting antibacterial activity against the fish pathogen Streptococcus agalactiae.