Katayoon Nofouzi - Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Ali Shaker - Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Najmeh Sheikhzadeh - Department of Food Hygiene and Aquatic Animals, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Gholamreza Hamidian - Department of Basic Sciences, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Amir Ali Shahbazfar - Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Mehdi Soltani - Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, WA, Australia

Background and Aim : The current research aimed at shedding light on the efficacy ofEscherichia coli strain Nissle ۱۹۱۷ (EcN) on goldfish growth, gut immunity, morphology, bacterialnutritional enzyme activity and resistance to Aeromonas hydrophila infection.Methods : Goldfish with mean weight of ۱.۸۱ g were fed the experimental diets including basaldiet (EcN۰), ۱۰۶ CFU g-۱ (EcN۱), ۱۰۷ CFU g-۱ (EcN۲) and ۱۰۸ CFU g-۱ (EcN۳) for ۸۰ days.The intestinal tissues (anterior, mid and posterior parts) were obtained from each fish and immuneassays, evaluation of immune related genes by q-RT-PCR, enumeration of bacteria related todigestion, and histological examination were performed. In the end, challenge experiment wascarried out by injecting A. hydrophila intraperitoneally to the remaining fish and the obtained datawas analyzed statistically.Results : The fish fed with E. coli at ۱۰۶, ۱۰۷ and ۱۰۸ CFU g-۱ showed an enhanced growthcompared to those fed with basal diet. Also, fish gut innate immunity, in terms of lysozymeactivity, immunoglobulin and total protein levels, was improved in the treatment fish better thanthose with basal diet, with the best result being observed in fish fed E. coli at۱۰۸ CFU g-۱. Inaddition, an increase was noted in the up-regulation of immune-relevant genes, namely lysozyme,interleukin -۱ß, inducible nitric oxide synthase and tumor necrosis factor ɑ of fish intestine treatedwith E. coli. A marked surge in the number of proteolytic and heterotrophic bacterial was noted inthe gut of fish nourished with the probiotic. Histological studies showed an improvement in theintestinal absorption surface area, intraepithelial lymphocyte count and goblet cell density of fishfed with probiotic-supplemental diets.Conclusion : These data exhibited the beneficial effect of E. coli on goldfish growth, digestiveenzymes and fish intestine heterotrophic bacteria, with the administration of E. coli at۱۰۸ CFU g-۱ yielding the most favorable results.

Escherichia coli, Goldfish, Gut microbiota, Mucosal immunity, Disease resistance