Evaluating the antimicrobial effect of isolated probiotic strains against Flavobacterium psychrophilum and their interference in the health status of rainbow trout (Oncorhynchus mykiss)

Abstract

The use of probiotic microorganisms for the prevention and treatment of bacterial infections in animals destined for human consumption, has been considered an efficient alternative to the use of antibiotics. In this context, the main objectives of the present study are the evaluation of antimicrobial effect against Flavobacterium psychrophilum and interference in health status in rainbow trout (Oncorhynchus mykiss) after supplementation with isolated probiotics. Three strains, identified as Lactococcus lactis (L1 and L2), with antimicrobial activities against fish and food pathogens and probiotic potential were selected to future investigations (in vivo). Compatibility tests between the selected strains were 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 micro-encapsulated 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 in order to provide a better understanding of the individual effects of these biomolecules on animal health. F. psychrophilum, the main agent of the rainbow trout syndrome, will be used as bioindicator. 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 and, once the animals triplicate their weight (15g), zootechnical parameters will be evaluated. In addition, histological analysis of intestine and liver will be performed to evaluate morpho-structural changes in these organs, as well as in vitro phagocytic activity of macrophages. (AU)