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Virulence of Flavobacterium psychrophilum, Antimicrobial Treatment and Intestinal Microbiota of Rainbow Trout Oncorhynchus mykiss

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Title: Virulence of Flavobacterium psychrophilum, Antimicrobial Treatment and Intestinal Microbiota of Rainbow Trout Oncorhynchus mykiss
Author: Jarau, Maureen
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Lumsden, JohnMacInnes, Janet
Abstract: Flavobacterium psychrophilum, the aetiologic agent of bacterial cold-water disease (BCWD), is responsible for significant economic losses in rainbow trout Oncorhynchus mykiss aquaculture. This thesis provides insights into the a) virulence potential of F. psychrophilum isolates from Ontario in rainbow trout, b) efficacy of oral treatment in controlling F. psychrophilum infection and c) impact of prophylactic treatment on the intestinal microbiota and subsequent susceptibility to BCWD. Following a preliminary infection trial, a broad range (0 to 63% mortality) of virulence was observed for 21 Ontario F. psychrophilum isolates. The virulent isolate FPG101 produced significant mortality (p < 0.05) at the infection dose of 108 cfu fish-1 compared to the control group. Plate counting rather than the rpoC qPCR assay was found to be more sensitive for detection of splenic F. psychrophilum. A minimum inhibitory concentration test showed little variation in the antimicrobial susceptibility of six virulent isolates of F. psychrophilum. One F. psychrophilum isolate with moderate susceptibility to erythromycin (FPG101) and another isolate with low susceptibility to erythromycin (FPG105) were used in an experimental infection trial. Relative to untreated controls, erythromycin treatment significantly (p < 0.05) reduced mortality of rainbow trout infected with FPG101. Erythromycin treatment was more effective than florfenicol treatment at splenic bacterial clearance during infection period. Furthermore, using Illumina Miseq sequencing, five bacterial phyla (Proteobacteria, Tenericutes, Spirochaetes, Fusobacteria and Firmicutes) plus “unclassified Bacteria” were identified as major constituents of the intestinal microbiota in rainbow trout throughout the experimental trial period. Before prophylactic oral treatment, Tenericutes and Proteobacteria were the most abundant phyla; Mycoplasma was the most abundant genus. No significant change was observed in the relative abundance of intestinal bacterial phyla after 10-day oral treatment with erythromycin. In contrast, oral treatment with florfenicol significantly increased (p < 0.05) Proteobacteria; Sphingomonas was the most abundant bacterial genus. Neither treatment increased the susceptibility of fish to subsequent F. psychrophilum infection.
Date: 2018-09
Rights: Attribution 2.5 Canada

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Attribution 2.5 Canada Except where otherwise noted, this item's license is described as Attribution 2.5 Canada