Attenuated acriflavin-fast Erysipelothrix insidiosa. Relationship between its capability to cause arthritis in mice and immunogenicity in swine

Abstract

Pathogenicity ar?d immuxaogenicity for mice were compared among eighteen Ery-sipelothrix insidiosa strains which had been attenuated by serial passages on acriflavimtagar culture, and those for pigs among nine of these strains.In the early stage of attenuation, all the original virulent Erysipelothrix insidiosastrains lost their virulence to kill mice. Arthritis occurred to the hind legs in all thesechronically infected mice. In this stage, the attenuated organisms were well propagatedin these mice, autd arthritis was induced constantly by inoculation with even a few dosesof these organisms.With the progress in attenuation, the organisms lost their ability to produce arthritisin mice gradually, although they still retained the immunogenicity for mice which wasdemonstrated by challenge made with a virulent strain ten days after immunization, After further attenuation, these organisms were no longer propagated in mice, aztdlost their immunogenicity completely.Inoculated with the organisms which had constantly caused arthritis in mice, pigsexlxibited clearer than those inoculated with the organisms which had notcaused arthritis in mice. They presented no other clinical abnormality during an observa-tion period of fourteen days after inoculation. The red patches disappeared within sevendays. These pigs survived against the challenge with virulent organisms, without mani-testing ar?y clinical symptoms during another observation period of fourteen days.Some of the strains had only a weak activity of producing arthritis in mice, but theysltowed a protection rate of more than eighty percent in mice against challenge with tltevirulent strain. They were proved to vary in degree of red-patch formation and give riseto only an insufficient immune status in pigs.After inoculation with strains which had lost an ability to produce arthritis or reducea protection rate to less than eighty percent in mice, no pigs were found to be immunxeagainst the virulent organisms.Tl?ere was 21 correlation between the immune statu