Biomedical Engineering Reference
In-Depth Information
to the thick, bilateral membrane. The most aggressive strains of the organism
produce a toxin, encoded by a phage (bacterial virus) in the genome. The toxin
contributes to tissue necrosis. Some cases of diphtheria involve the skin.
Readers should be aware of the highly confusing term, “diphtheroid,” com-
monly applied to all the non-pathogenic species within Genus Corynebacterium.
As non-pathogens, the diphtheroids do not cause diphtheria. Diphtheria is caused
Corynebacterium diphtheriae (i.e., a non-diphtheroid).
Species in Genus Dermatophilus produce skin lesions in a variety of
animals, including humans [58]. Pitted keratolysis is a skin condition charac-
terized by the appearance of discoloration on the palms or the plantar
surfaces, with superficial craters. It may arise from various species of Genus
Dermatophilus, Dermatophilus congolensis among them [59]. The organisms
are found in the environment, and human-to-human contagion does not seem
to be a mode of transmission.
About 2 billion people (of the world's 7 billion population) have been
infected with Mycobacterium tuberculosis. Most infected individuals never
develop overt disease. Nonetheless, tuberculosis kills about 3 million people
each year [4]. Disease is transmitted from humans who have active,
untreated disease, often by aerosolized droplets. The disease usually presents
as a granulomatous process in the lungs. Multi-organ involvement may occur
if the lung disease is not adequately treated. Aside from Mycobacterium
tuberculosis, several other species may cause a tuberculosis-like disease.
These species include: Mycobacterium bovis, Mycobacterium africanum,
Mycobacterium canetti, and Mycobacterium microti.
Mycobacterium xenopi produces a chronic pulmonary disease simulating
tuberculosis. M. xenopi does not seem to be transmitted from person to person.
The organism has been isolated from water and soil, and the presumed mode
of transmission is through environmental exposure. Though the disease is cur-
rently rare in the USA, cases are not unusual in England, Europe, and Canada.
Leprosy, also known as Hansen's disease, is caused by Mycobacterium
leprae and Mycobacterium lepromatosis. The disease produces granulomas
in the skin, including the nerves of the skin, and the respiratory tract.
Untreated leprosy is slowly progressive. Most human cases seem to be trans-
mitted by aerosolized droplets produced by actively infected and untreated
patients. It is believed that animals, particularly the armadillo, are potential
reservoirs. New cases of leprosy have been dropping. In 2005, there were
about 300 000 new cases reported, worldwide [60].
Mycobacterium ulcerans causes Buruli ulcer, a skin condition seen in
the tropics. Mycobacterium ulcerans produces a toxin, mycolactone, that
is responsible for most of the tissue destruction observed clinically. Other
mycobacteria that produce mycolactone include Mycobacteria liflandii,
Mycobacteria pseudoshottsii, and strains of Mycobacteria marinum. The
disease does not appear to be spread from human to human; aquatic insects
are the suspected vectors.
