M. paratuberculosis

This is also known as bacillus of Johne’s disease and is

the cause of a chronic enteritis in cattle and sheep. The

primary isolation is difficult and medium has to contain

mycobactin—an extract from other mycobacteria.

M. ulcerans

This produces a chronic or subacute ulceration in both the

skin and the adjacent subcutaneous tissue, particularly of

legs and arms. Incubation temperature should be between

25 and 35°C and the best growth is at 33°C. It grows on

glycerin agar.

M. balnei

This bacillus has been isolated from swimming pools and

produces ulcerative lesions on the extremities. It grows

more rapidly than M. ulcerans, but will not grow above 35°C.

M. leprae

This is also known as Hansen’s bacillus and causes leprosy.

Smears are made from a scraping from the skin of suspected

lesions and from nasal smears. It has been found in sputum.

The usual method is skin clips from the affected areas.

Films are stained by Z-N stain, but it is customary to

use 5% sulfuric acid for decolorizing as M. leprae is not so

strongly acid fast as M. tuberculosis, but stained M. leprae

bacilli may resist decolorization with 20% sulfuric acid. The

bacilli are usually present in large numbers (in lepromatous

leprosy) and are generally found in packets like cigar

bundles within phagocytic cells called lepra cells. They

may stain uniformly but there is often marked beading. The

bacilli may also be stained fairly easily by Gram’s method.

Until recently, no claims of culture were substantiated,

but it is now believe that the organism may be isolated on

the footpads of mice.