In Vitro and In Vivo Evaluation of Potassium Permanganate Treatment Efficacy for the Control of Acute Experimental Infection by Flavobacterium columnare in Channel Catfish

Abstract

An experiment was performed to evaluate the in vitro and in vivo efficacy of potassium permanganate (KMnO₄) against Flavobacterium columnare. In vitro, F. columnare treated with KMnO₄ at 2 mg/L for 8 h exhibited a 70% reduction in colony-forming units (CFU). A minimum KMnO₄ concentration of 10 mg/L was needed to inhibit bacterial growth. An acute and systemic experimental infection was produced in channel catfish Ictalurus punctatus by waterborne exposure to the bacteria after mechanical cutaneous abrasion to remove mucus and epithelium. At 22 h postchallenge, an 8-h treatment with KMnO₄ at 2.3 mg/L (2.0 mg/L above the average KMnO₄ demand of 0.3 mg/L) was initiated. This did not reduce mortality in experimentally infected fish. The infection model utilized in the experiment was evaluated by examining the clinical signs and histopathology of infected fish. Fish in the model showed columnaris signs similar to those of a natural infection, including skin depigmentation and ulceration and gill necrosis. Histologically, the skin had severe ulcerative necrotizing dermatitis and the muscles had severe necrotizing myositis. The gills had severe multifocal necrotizing branchitis involving the lamellar and filament epithelium, pillar cells, and central venous sinus. Heavy bacterial aggregates of long rods were associated with the necrotic cellular debris. The identity of the bacteria isolated from the challenged fish was confirmed by polymerase chain reaction. The results suggest that KMnO₄ is beneficial for reducing F. columnare load in the water column and possibly on fish, but the therapeutic value of KMnO₄ is limited in fish with an acute and systemic columnaris infection. Further research is warranted to investigate the value of KMnO₄ as a therapeutic agent for fish with a milder columnaris infection and as a treatment to prevent further spread of columnaris in a fish population.