Two acriflavine-fast attenuated Erysipelothrix rhusiopathiae strains Koganei 65-0.15 of serotype 1a (strain Kg-1a) and 2 (strain Kg-2) were comparatively characterized. Biochemical characterization showed the similar reactions with slight variation between the strains. Strain Kg-2 was more resistant to acriflavine dye than strain Kg-1a. Pathogenicity of strain Kg-2 was higher than strain Kg-1a in mice of strains ddY. C3H/He and A/J. Significant differences of clinical signs between strains Kg-1a and Kg-2 were observed in occurrence of arthritis (P < 0.05) and systemic signs (P < 0.01) of only ddY mice. C3H/He mice was more resistant than ddY and A/J mice to the infection of strains Kg-1a and Kg-2. Three culture fractions, whole culture: WC, culture filtrate: CF and killed cells: KC, of strain Kg-2 were more protective than those of strain Kg-1a in ddY mice. CF of strain Kg-2 was most protective in all fractions. Heating at 56 degrees C and 100 degrees C or treatment with trypsin completely reduced the protective activity of WC of the two strains, indicating that major protective antigens of WC were protein. The present results demonstrated that immunogenicity and pathogenicity for mice were different between the two attenuated strains.
