Mycobacterium leprae, also known as Hansen’s bacillus, is the bacterium that causes leprosy (Hansen's disease). It is an intracellular, pleomorphic, acid fast. M. Leprae is a gram-positive aerobic rod 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 carbon finishing rather than with the traditional Gram stain. The culture takes several weeks to mature.

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

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

It has not been possible to culture M. 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. The bacterium can infect armadillos, so it is studied in them (sometimes to the vexation of "animal ethicists"). See and [http://www.uow.edu.au/arts/sts/bmartin/dissent/documents/Burchfield/alc13.html

Virulence factors include a waxy exterior coating, formed by the production of mycolic acids unique to Mycobacteria.

M. leprae is sensitive to dapsone (diaminodiphenylsulfone, the first effective treatment which was discovered for leprosy in the 1940's), but resistance against this antibiotic has developed over time. Therapy with dapsone alone is now strongly contraindicated. Currently, a multidrug treatment (MDT) is recommended by the World Health Organization, including dapsone, rifampicin and clofazimine. In patients receiving (MDT), a high proportion of the bacilli die within a short amount of time without immediate relief of symptoms. This suggests that many symptoms of leprosy must be due in part, to the presence of dead cells.

External links

• The genome of Mycobacterium leprae
• "Mycobacterium leprae" Quick Reference

Actinobacteria | Leprosy

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