Biomedical Engineering Reference
In-Depth Information
The atypical mycobacteria are a group of about 13 organisms that are
found in soil and water, as pathogens in animals, or even as commensals
growing in the pharynx of humans. Diseases, when they occur in otherwise
healthy individuals, tend to be mild, involving skin, lungs, or lymph nodes.
The atypical mycobacteria pose a serious problem in immune-compromised
patients, particularly those with AIDS. Organisms in the Mycobacterium-
avium-intracellulare complex,
found throughout
the environment, are a
particular threat for patients with advanced AIDS.
Genus Nocardia contains dozens of species that cause disease in animals.
In humans, Nocardia organisms are opportunistic pathogens affecting children,
the elderly, immune-compromised individuals, and patients with a pre-existing
serious disease. Nocardia asteroides is the most common cause of human
nocardiosis. Pneumonia is a common presentation of nocardiosis. Encephalitis,
endocarditis, abscess formation, and sepsis are also seen. Nocardiosis brasi-
liensis has been implicated in some cases of mycetoma. A full discussion of
mycetoma is found under Genus Neotestudina (Ascomycota, Chapter 36).
Readers should not be confused by the plethora of organisms with “brasi-
liensis” as the species of the binomen. These include Nocardia brasiliensis,
Leishmania
brasiliensis
(alternately
spelled Leishmania
braziliensis),
Paracoccidioides brasiliensis, and Borrelia brasiliensis.
Rhodococcus equi is the cause of foal pneumonia, or rattles, in young
horses. It can infect immune-compromised humans, causing a disease that
closely simulates tuberculosis.
Actinobacteria
Actinomycetales
Cellulomonadaceae
*Tropheryma
The only pathogenic species in Class Cellulomonadacea is Tropheryma
whipplei, the cause of Whipple disease. As a general rule, bacteria in the
human body are eaten by macrophages, wherein they are degraded. In the
case of Tropheryma whipplei, certain susceptible individuals have a problem
with degradation of the organism within macrophages. Consequently, the
organisms multiply within macrophages. When organisms are released from
dying macrophages, additional macrophages arrive to feed, but this only
results in the local accumulation of macrophages bloated by bacteria.
Whipple disease is characterized by the infiltration of organs by foamy
macrophages containing Tropheryma whipplei. The organ most often com-
promised is the small intestine, where infiltration of infected macrophages
in the lamina propria (the connective tissue underlying the epithelial lining
of the small intestine) causes malabsorption. Whipple disease is quite rare.
It occurs most often in farmers and gardeners who work with soil, in which
the organism lives. As recently as 1992, the cause of Whipple disease was
unknown [61].
