Mycobacterium leprae is not a bacteria commonly known in the United States. It is found in tropical countries primarily. This bacteria is a rod-shaped organism that is aerobic, meaning that it requires oxygen to survive. Very similar to Mycobacterium tuberculosis, the two organisms appear similar with their shape and characteristics, but have much different effects on the human body.
Mycobacterium leprae is most commonly associated with the disease leprosy. Leprosy is a particularly dangerous disease since the causative agent is difficult to eradicate, especially from the human body. The bacterium has a waxy coating which will resist gram-staining, one of the first ways that an organism is identified. It can take weeks to positively identify the organism as Mycobactium leprae.
The bacteria is an intracellular bacteria, meaning that it lives inside a host cell. When the bacteria enters the human body, the protective cells of the body recognize it as foreign and engulf it, in a process known as phagocytosis. Since the bacteria have a waxy outside, they can resist the lysosomes that the white blood cell secretes to destroy the bacteria and will survive. Inside the host cell, Mycobacterium leprae will multiply and, in essence, take over the functional parts of the white blood cell, to use for its own purposes. When the cells have duplicated and are ready to infect new cells, the bacteria will destroy the white blood cell, and release the new cells into the human body, allowing for further infection.
Although leprosy is a disease that has existed for hundreds, even thousands, of years, the causative agent of leprosy was not known until the 1870s. A Norwegian physician by the name of Hansen took samples of the leprous patches from those with leprosy and examined the skin cells to find the bacteria living there.
Although identifying the bacteria was accomplished, actually studying and reproducing the leprosy causative agent proved to be more difficult. Mycobacterium leprae cannot be grown on a medium in a lab, only on other living organisms. Scientists have been able to infect mice and armadillos with the disease, since they have enough characteristics of humans to host the organism. There are some antibiotics available, although some drug-resistant strains do exist.