Mycobacterium leprae, also known as Hansen’s bacillus, is the bacterium that causes leprosy (now called Hansen's disease). It is an intracellular, pleomorphic, but usually rod shaped, acid fast, Gram positive, aerobic only remotely and only morphologically related to Mycobacterium tuberculosis.

Optical microscopy shows clumps, rounded masses, or in groups of bacilli side by side.

It was discovered in 1873 by the Norwegian physician Gerhard Henrik Armauer Hansen, who was searching for the bacteria in the skin nodules of patients with leprosy.

It has not been possible to culture Mycobacterium leprae on artificial culture media, but it can be cultivated transiently in the mouse footpad. This can be used as a diagnostic test for the presence of bacillus in body lesions of suspected leprosy patients.

Mycobacterium leprae is sensitive to dapsone (the first effective treatment which was discovered for leprosy), but resistance against this antibiotic has developed along time. Currently, a multidrug treatment (MDT) is recommended by the World Health Organization, including dapsone, rifampicin and clofazimine.

Links

• The genome of Mycobacterium leprae  (http://www.sanger.ac.uk/Projects/M_leprae)

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