This is a report on attempts tp search for a suitable experimental animal model which is sensitive to the exocellular substances of M. ulcerans, prior to study of biochemical and pathogenic natures of the substances.

Cells of M. ulcerans grown in a broth medium were harvested by filtration and washed with phosphate-buffered saline. The filtrate of culture supernatant was subjected to fractionation by addition of various amounts of ammonium sulfate. The washed cells and the preparations resulted from ammonium sulfate fractionation (ASF 45 and ASF 70) were inoculated by either foot-pad injection, subcutaneous or intradermal injection to the selected animal groups. Any skin response due to administration of the preparations; erythema, edema, pus formation, etc. was macroscopically observed along with time progression.

Among the animals employed, such as guinea pig, mouse, and rabbit, the rabbit was the only animal group showing strong skin response to the washed cells, ASF 45 and ASF 70. The heat-treated preparation of ASF 45 seemed to be inactive in elucidating skin response of rabbits. Dependence of skin response upon dose of the washed cells and the preparation of ASF 45 was also discussed.