Mycobacterium leprae, also known as Hansen’s bacillus spirilly, mostly found in warm tropical countries, is a Gram-positive bacterium that causes leprosy (Hansen's disease). It is an intracellular, pleomorphic, acid-fast, pathogenic bacterium. M. leprae is an aerobic bacillus (rod-shaped) surrounded by the characteristic waxy coating unique to mycobacteria. In size and shape, it closely resembles Mycobacterium tuberculosis. Due to its thick waxy coating, M. leprae stains with a carbol fuchsin rather, than with the traditional Gram stain. The culture takes several weeks to mature.