Intensive aquaculture operations often face significant economic losses due to stress-induced disease outbreaks. In response, antibiotics have been extensively utilized to combat infections . However, this widespread use of antibiotics, especially in frequent or low doses, elevates the risk of antibiotic-resistant bacteria emergence. Consequently, there is a pressing need to explore alternative strategies. Thus, this study focuses on assessing the probiotic potential of single and multistrain consortia isolated from the intestinal microbiota of tilapia ( O. niloticus).
Bacteria were isolated and underwent an extensive screening procedure to determine their probiotic capabilities. This involved assessing their ability to withstand low pH conditions, tolerate bile salts, display hydrophobic properties, and exhibit antimicrobial activity against prevalent pathogens like Streptococcus agalactiae and Aeromonas hydrophila . From the isolated strains, Lactococcus lactis A12, AMB7, Priestia megaterium M4, and Priestia sp. M10 emerged as promising candidates (see Figure 1).
Potential probiotics were also evaluated in vivo by oral administration of single or multistrain bacterial consortia to Nile tilapia alevins. Growth performance, intestinal histology, microbiome composition , resistance to S. agalactiae during an experimental challenge, and immune response was studied by transcriptomics analysis .
All treatments improved growth performance, microvillus length, and survival during experimental infection with S. agalactiae . Moreover, they showed modulation of immune system-related pathways such as Neutrophil extracellular trap formation, Fc gamma phagocytosis, leukocyte transendothelial migration, and natural killer cell activity, among others (Figure 2) . These findings demonstrate synergistic modes of action beneficial for fish.
References
Melo-Bolívar, J. et al. (2023). Fish and Shellfish Immunology
Melo-Bolívar, J. et al. (2022 ). Microorganisms