Biological Study of “R”and “S”Forms of Chromogenic Acid-Fast Bacillus from Human Leprous Lesion

Abstract

Summary

The “R”and “S”forms of the lepra bacillus show definite biological differences. The “S”form is a smooth and moist colony while the “R”form is wrinkled and dry. The “R”form grows the more rapidly, forms a flaky suspension and is more thermostable. After several months of subculturing, both forms remained pure. The “S”form are acid-fast rods the majority of which contain 2–5 small granules. The “R”form are short rods showing a predominance of large bipolar granules and surrounded by a thicker capsular zone. The significance of the small granules in the “S”form and the large polar granules in the “R”form is not fully understood. It is reasonable to believe that the small granules in the “S”form are signs of degeneration while the large granules in the “R”form may represent a stage of quiescence resembling a spore stage. The presence of the much thickened capsular zone and the higher thermal death-point in the “R”form may have some relation to its stability and resistance to disintegration.

Since the “S”form reverts to the “R”during its adaptation on artificial media and the “S”variant can later be isolated from the “R”it must be assumed the “S”and “R”are reversible. The “S”being the typical and the “R”the mutant form.