Development of a Nile tilapia (Oreochromis niloticus) gut microbiota-derived bacterial consortium with antibacterial activity against fish pathogens

Multistrain potential probiotic mixtures were assembled from isolates from Nile tilapia (O. niloticus) gut microbiota. Lactococcus lactis A12, Priestia megaterium M4, and Priestia sp. M10 demonstrating antibacterial activity against two fish pathogens, Streptococcus agalactiae and Aeromonas hydrophila, were proportion optimized using mixture design software. Two potential probiotic mixtures were chosen and compared for storage viability: one containing 61% of strain A12, 16% of M4, and 23% of M10; the other containing 28% of M4 and 72% of M10. The mixtures were combined with maltodextrin or fish feed, freeze-dried, and bacterial counts were monitored over 28 days while stored at 4 °C or 25 °C. At 4 °C storage, the multistrain potential probiotics were stable in maltodextrin and fish feed. In conclusion, a mixture design may be used to define a multistrain potential probiotic, and freeze-drying while combined with maltodextrin or fish feed followed by refrigeration could be employed to stabilize these tilapia-derived potential probiotics.