Evaluating the potential of bacteriocinogenic lactic acid bacteria isolated from Rainbow Trout (Oncorhynchus mykiss): antimicrobial effect against Flavobacterium psychrophilum

Abstract

The use of probiotic microorganisms for thuhe prevention and treatment of bacterial infections in animals destined for human consumption, has been considered an efficient alternative to the use of antibiotics. In addition, recent studies have shown that certain biomolecules produced by these microorganisms, such as bacteriocins, vitamins, fatty acids, exopolysaccharides and enzymes, improve the immunity and development of their hosts. The most currently used probiotic microorganisms in food and pharmaceutical industries are the Lactic Acid Bacteria group (LAB). These bacteria are considered safe by regulators in this area. However, it is known that their beneficial effects are specific to each host and that each beneficial biomolecule is produced, in major quantities, by a specific strain. In this context, the main objectives of the present study are the isolation and identification of probiotic LABs from the intestinal microbiota of rainbow trout (Oncorhynchus mykiss). Strains with high bacteriocin activities and probiotic potential will be selected and fermentation cultures will be prepared, using agro-industrial residues, such as sugarcane bagasse, as substrate. The fermentation will be performed in a 3L bench-top bioreactor, in fed-batch operation mode, to optimize the bioprocess system. Compatibility tests between the selected strains will be carried out, and, basing on the results, a probiotic bacterial mixture will be prepared. To verify the probiotic effect of the mixture, each composing strain will be individually microencapsulated and administered daily in the diet of rainbow trout fingerlings of approximately 5.0 g total weight, through ration at the dosage of 2% of their body weight. Synthetic bacteriocins will also be micro-encapsulated and administered to the fingerlings (alevinos) in order to provide a better understanding of the individual effectsof these biomolecules on animal health. The results obtained with the use of the microcapsules will be compared to those obtained without the administration of the microcapsules. The fingerlings will be kept in fiberglass tanks; the concentration and saturation of oxygen and the water temperature will be determined daily. Once the animals triplicate their weight (15g), zootechnical parameters will be evaluated, such as weight increase, growth, conversion factor and survival. In addition, histological analyzes of intestine and liver will be performed to evaluate morpho-structural changes in these organs, as well as in vitro phagocytic activity of macrophage (AU)