Mycobacterium leprae
Cassandra Partin

Mycobacterium leprae is a rod-shaped bacterium that causes the disease leprosy. It does not form capsules, flagella, or spores. It was first detected in 1873 by a Norwegian physician named Gerhard Hansen and is sometimes called Hansen's bacillus in his honor.

M. leprae's general morphology and staining characteristics are similar to other mycobacteria. Therefore, it is acid-fast, meaning that an acid-alcohol solution won't remove carbol fuchsin dye from its cell wall. Its cells contain peptidoglycan and stain gram-positive, but most of its cell wall is comprised of unique types of lipids. One of the fatty acid chains is mycolic acid. The thick, waxy nature imparted by these lipids causes high resistance to certain chemicals and adds to its pathogenicity. There are two notable exceptions to its similarity to other mycobacteria. The first is that it's a strict parasite that has not been grown in artificial media or human tissue cultures. The second is that it is the slowest growing of all species. Its generation time is anywhere from ten to thirty days. M. leprae multiplies within host cells in large packets called globi at an optimum temperature of 30 C

The leprosy bacillus is not highly virulent so most people who come into contact with it don't develop the disease. The bacterium does have some highly effective evasion mechanisms which helps it avoid different aspects of phagocyte mediated killing. One mechanism is that it surrounds itself with phenolic glycolipid which scavenges free radicals. It also releases a lipoarabinomannan, which blocks the ability of macrophages to respond to the activating effects of IFNgamma. Infected cells may also lose their efficiency as antigen-presenting cells. Finally, M. leprae can escape from the phagosome to multiply in the cytoplasm. The actual disease is treated with dapsone, rifampin, and clofazimine (usually in combination).


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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