Tuberculosis is a bacterial
infection that produces blood in sputum and is caused by several species of
mycobacterium collectively called tubercle bacillus. Tuberculosis in human is
caused by variety of bacillus of which the most prevalent is mycobacterium tuberculosis (WHO/TB
1997).
Mycobacterium belongs to the
family of mycobacteriaccae. mycobacteria are straight or slightly
curved rods, however, coccobacillary, filamentious and branching forms also occur.
The name mycobacterium (fungus – bacterium) was derived from the mould-like
pedicle formed when members of this genus are
grown in liquid media (Lehmann
and Newmann, 1896). This hydrophilic property is due to their thick, complex,
lipid-rich waxy cell walls. Due to their waxy cell walls they are difficult to
stain, but once stained with hot carbol fulchsin
or other aryl methane dyes, they resist decolorization with dilute mineral acids
and alcohol.
They are therefore known as acid fast bacilli (AFB). Only the
members of the genus mycobacterium, a
few species of Norcardia and bacterial spores posses this property. They are
gram- positive, but some species are stained poorly even after prolonged staining.
They are aerobic or micro aerophilic non motile and non- sporing. Some strains
produce yellow pigment in the dark or after exposure to light. The first member
of this genus to be identified was the lepra bacillus by 1874. Eight years later, Robert Kochs (1882) isolated the mammalian tubercle
bacillus and proved its causative role in tuberculosis by Kocks postulates.
The
genus mycobacterium comprises seventy
one recognized species, the most familiar of the species are m. tuberculosis and m. leprae , the causative agents of tuberculosis and leprosy
respectively. Both diseases have been associated with chronic illness and
social stigma. (D.R Arora, 2004).
Mycobacterium
that infects humans
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Species
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Reservoirs
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Common clinical manifestation
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m. tuberculosis
m. Leprae
m. bovis
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Humans
Humans
Humans
and cattle
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Pulmonary
and disseminated tuberculosis millions of cases annually in the world.
Leprosy.
Tuberculosis-like
disease rare in North America. m. bovis
is closely related to m. tuberculosis.
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