as a new species. In general, most authors have considered their own strains to be M. ulcerans wherever they were isolated, but no comparative study of strains from a number of countries in which the disease occurs has been made. The chief difficulty in undertaking a taxonomic study of these organisms is their plethora of negative reactions in the majority of tests that are applied to slow-growing mycobacteria. For the present study, inmunodiffusion analysis, a method of high species-differentiathe value among$ mycobacteria, has alone been used.
MATERIALS AND METHODSThe strains. There were four strains from Australia, including NCTC no. 10417 (type strain of Mycobacterium ulcerans) and NCTC no. 10013; two strains from Malaya; one strain from Mexico; 17 strains from Uganda, including NCTC no. 10445 (type strain of M. buruli); and 11 strains from Zaire.Methodr. Antigens were prepared from each strain and antisera were raised to seven of them (NCTC no. 10013 and two other Australian strains; NCTC no. 10445 and another Ugandan strain; two Zairian strains). Two 60-ml bottles each containing 30 ml of Lowenstein-Jensen medium sloped to give a large surface area were inoculated with each strain and incubated at 32°C until good growth was obtained; this time varied from 4 to 8 wk. The organisms were carefully scraped from the medium and suspended in 5 ml of normal saline. These suspensions were then treated for 15 min. in an M.S.E. 100-watt ultrasonic disintegrator set at a peak distance of 8 pm, and the resulting material was used without further treatment in immunodiffusion tests. Because of the contamination with egg protein from the medium, strains used for raising antisera were treated as follows before ultrasonic disintegration. To each suspension of organisms in saline was added an equal volume of a mixture of 1 part heptane and 1 part Whitemor oil, and this was shaken until an emulsion formed. The emulsions were stood at 4°C overnight to separate and the suspensions of organisms in oil were washed several times in distilled water. The suspensions were centrifuged at 3000 r.p.m. for 20 min. and the supernatant oil was discarded. The deposited organisms were washed twice in acetone, resuspended in 5 ml of normal saline ~~