Ineffectiveness of iodophore treatment in disinfecting salmonid eggs carrying Cytophaga psychrophila

Eggs of coho salmon (Oncorhynchus kisutch), rainbow trout (O. mykiss), and masu salmon (O. masou) were artificially inserninated and subsequently immersed in a modified Ordal and Anacker's broth culture of Cytophaga psychorophila (10(7)-10(8) CFU/ml) for 30 min. The bacterium was recovered from the eggs at the eyed stage with viable cell counts ranging from 10(5) to 10(7) CFU/g. The fertilized eggs were disinfected with 50 ppm povidone-iodine for 15 min immediately after experimental infection. However, C. psychrophila was detected by a broth culture method from 60-80 percent of the surface-disinfected eggs. At the eyed stage, the eggs were disinfected again with povidone-iodine at concentrations of 50-1,000 ppm for 15-120 min. C. psychrophila was isolated from all of them at densities of 10(4)-10(7) CFU/g. The uninfected control eggs were all negative for the bacterium. It is concluded that the povidone-iodine treatment is ineffective to eliminate C. psychrophila from salmonid eggs.