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''Mycobacterium leprae'', also known as Hansen’s coccus 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 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. Optical microscopy shows ''M. leprae'' in clumps, rounded masses, or in groups of bacilli side by side, and ranging from 1–8 μm in length and 0.2–0.5 μm in diameter. 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 was the first bacterium to be identified as causing disease in humans. The organism has never been successfully grown on an artificial cell culture medium.〔 Instead, it has been grown in mouse foot pads and more recently in nine-banded armadillos because they, like humans, are susceptible to leprosy. This can be used as a diagnostic test for the presence of bacilli in body lesions of suspected leprosy patients. The difficulty in culturing the organism appears to be because it is an obligate intracellular parasite that lacks many necessary genes for independent survival. The complex and unique cell wall that makes members of the ''Mycobacterium'' genus difficult to destroy is apparently also the reason for the extremely slow replication rate. Virulence factors include a waxy exterior coating, formed by the production of mycolic acids unique to ''Mycobacterium''. ''M. leprae'' was sensitive to dapsone (diaminodiphenylsulfone, the first effective treatment which was discovered for leprosy in the 1940s), 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 the MDT, a high proportion of the bacilli die within a short amount of time without immediate relief of symptoms. This suggests many symptoms of leprosy must be due in part to the presence of dead cells. == Pathogenesis == The incubation period of ''M. leprae'' can range between nine months and twenty years. It replicates intracellularly inside histocytes and nerve cells and has two forms. One form is ''tuberculoid'', which induces a cell-mediated response that limits its growth. Through this form ''M. leprae'' multiplies at the site of entry, usually the skin, invading and colonizing Schwann cells. The microbe then induces T-helper lymphocytes, epitheloid cells, and giant cell infiltration of the skin, causing infected individuals to exhibit large flattened patches with raised and elevated red edges on their skin. These patches have dry, pale, hairless centers, accompanied by a loss of sensation on the skin. The loss of sensation may develop as a result of invasion of the peripheral sensory nerves. The macule at the cutaneous site of entry and the loss of pain sensation are key clinical indications that an individual has a tuberculoid form of leprosy. The second form of leprosy is the ''lepromatous'' form. This form of the microbe proliferates within the macrophages at the site of entry. It also grows within the epithelial tissues of the face and ear lobes. The suppressor T-cells that are induced are numerous, however the epithelioid and giant cells are rare or absent. With cell-mediated immunity impaired, large numbers of ''M. leprae'' appear in the macrophages and the infected patients develop papules at the entry site, marked by a folding of the skin. Gradual destruction of cutaneous nerves lead to what is referred to as "classic lion face." Extensive penetration of this microbe may lead to severe body damage; for example the loss of bones, fingers, and toes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mycobacterium leprae」の詳細全文を読む スポンサード リンク
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