Diseño de nuevos productos postbióticos para su aplicación en la acuicultura de trucha arcoíris
Authors:   , Quintanilla Pineda Mario Alejandro 
Published: July 2024

The use of postbiotics as biological control tools is based on utilizing metabolic products derived from the controlled culture of microorganisms. These postbiotics can enhance the health of the animals that consume them. Representing an affordable, safe, and natural option that promotes animal well-being due to its easy administration, particularly in aquaculture. In this context, this thesis aims to develop an innovative postbiotic product that benefits the aquaculture industry and improves the health of rainbow trout, addressing the selection of microorganisms, postbiotic production, and product efficacy evaluation under in vivo conditions. Therefore, the following objectives were proposed: (1) to select bacterial isolates obtained from fish based on their ability to inhibit the pathogens Aeromonas salmonicida subsp. salmonicida and Yersinia ruckeri for the design of the postbiotic product; (2) to standardize of the manufacturing process of the postbiotic product at a laboratory scale, assessing changes in the product's characteristics under different experimental conditions; (3) to investigate the product's effectiveness in vivo , analyzing the impact of administering feed supplemented with postbiotics on the health of rainbow trout; (4) to determine the effect of the postbiotic product on resistance to yersiniosis and furunculosis through experimental infection models. To isolate candidate microorganisms for the design of the postbiotic product, tissue samples from rainbow trout (Oncorhynchus mykiss) and Nile tilapia (Oreochromis niloticus) were collected. The obtained microorganisms were assessed in vitro against A. salmonicida subsp. salmonicida and Y. ruckeri, selecting those with the highest antibacterial activity. Subsequently, these microorganisms were identified and used to produce the postbiotic product. The product's ability to retain the previously reported antibacterial activity was determined through co-culture challenges and microdilution assays. Two bacteria were selected for the postbiotic production process, and their survival in different pH levels and rainbow trout bile salt percentages, hydrophobicity, and enzymatic potential were profiled. Additionally, the postbiotic product was manufactured under different experimental conditions to assess the synergy between the two microorganisms, the influence of incubation time before inactivation, and the impact of the culture medium on antimicrobial activity. The product was also subjected to various temperatures and proteolytic enzymes to determine its thermosensitivity and the contribution of protein fractions to its antimicrobial activity. An in vivo experiment was conducted where rainbow trout were fed with feed supplemented with 0.5% postbiotic and unsupplemented feed, and samples were taken at specific time points during the supplementation period. To study the immunomodulatory effect, samples from the head kidney were collected, and the expression of five cytokines was studied using real-time quantitative polymerase chain reaction (RT-qPCR). To study changes in the intestinal microbiota, samples of intestinal mucus were collected and processed in selective culture media to evaluate changes in the concentrations of lactic acid bacteria and total aerobic bacteria. At the end of the study, the fish were weighed to determine changes in final weight. Finally, the animals of the feeding trial were subjected to experimental infections with the pathogens A. salmonicida subsp. salmonicida and Y. ruckeri to determine changes in survival and determine whether the supplemented feed contributes to improving the animals' resistance to yersiniosis and furunculosis. A total of 369 microorganisms were isolated from the initial samples, of which 12 were identified. Four belonged to Pediococcus acidilactici, seven to W. cibaria, and one to Weissella paramesenteroides. Postbiotics were produced using these isolates, and it was determined that two isolates of W. cibaria exhibited the highest antibacterial activity against the target pathogens. It was confirmed that proteins in the postbiotic product were primarily responsible for its antibacterial activity. Despite a partial loss of effectiveness during the manufacturing process in vegetal culture media, co-cultivation, and exposure to heat, the antibacterial activity remained significant. Feeding with postbiotic-supplemented feed increased the concentrations of lactic acid bacteria in the rainbow trout's intestine. Additionally, modulation in the expression of proinflammatory cytokines and an improvement in survival against Y. ruckeri and A. salmonicida subsp. salmonicida were observed. Continued progress in the research of alternatives to antibiotic use is essential, with a particular focus on developing postbiotics applicable in aquaculture and other areas of animal production. These innovative options aim not only to replace antibiotics but also to eradicate their use in animal farming, with the goal of preventing the spread of resistance genes in animals, their environment, and ultimately, consumers.