Term
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Definition
Mycobacterium
A large genus of acid-fast, aerobic, thin, irregular rods
that have large amounts of a large lipid called mycolic
acid in their cell wall. There are about 75 species.
2. Mycolic acid constitutes about 50% of the cell wall
weight of mycobacteria and conveys a number of unique characteristics to them,
Slow growth. rough, tightly matted colonies on agar
media and surface pellicles in broth media.
C. Protection from killing inside phagocytic cells.
D. Capacity for intracellular growth inside phagocytes.
E. Resistance to Gram-staining, detergents, many
antimicrobial drugs, dessication and acid-fastness |
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Term
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Definition
Virulence Factors of M. tuberculosis
1. M. tuberculosis produces no toxins or destructive
hydrolytic enzymes. Its virulence stems from:
A. Its ability to survive & replicate inside macrophages.
B. Its activation of destructive host immune responses
*These virulence properties are conveyed by various mycolic acid containing compounds called mycosides that are present in the cell wall of M. tuberculosis.* |
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Term
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Definition
All virulent strains of M.tuberculosis produce a mycoside called cord factor that causes M.tuberculosis cells to stick to each other and grow as large serpentine cords.
causes severe inflammation,
wasting and death in mice that are injected with it.
1) Cord factor does this occurs by activating macrophages
to secrete excessive quantities of the inflammatory
cytokine tumor necrosis factor α, which enters the
circulation and causes inflammation, shock and death. |
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Term
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Definition
Mycosides called sulfitides inhibit phagosome-
lysosome fusion in macrophages and enhance survival
of ingested M. tuberculosis cells in macrophages |
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Term
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Definition
A complex mycoside called wax D is a potent
immunological adjuvant that induces cellular
immunity and delayed hypersensitivity to proteins.
A. Delayed hypersensitivity to proteins produced by M.
tuberculosis causes most of the tissue destruction that
occurs in active tuberculosis infection. |
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Term
TB has 4 clinical forms depending upon route of
infection & the state of the host immune response. |
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Definition
A. Primary TB is the initial M. tuberculosis infection in
the lungs. It results in an arrested infection in 95% of
hosts; the other 5% develop progressive primary TB.
B. Secondary (reactivation) TB is the reestablishment of
active TB in the lungs after a period of dormancy which
can be short or long in duration depending on the state
of the host’s cellular immunity. About 10% of infected
hosts develop reactivation TB, usually within 2 years.
C. Disseminated (Miliary) TB is the spread of active TB
throughout the body to many internal organs and tissues
via the bloodstream.
D. Ingestion TB is TB of tonsils, intestinal lymph nodes,
cervical lymph nodes (scrofula) and bones. It is caused
by ingestion of M. bovis or M. tuberculosis. |
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Term
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Definition
Primary Tuberculosis granulomas are called tubercles.
contain live TB bacilli
and necrotic, semi-solid tissue
that resembles Swiss cheese.(caseous necrosis) |
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Term
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Definition
In TB Large calcified primary complex
lesions are visible by X-ray & are
called the Ghon complex. About 25% of infected host develop |
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Term
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Definition
dissemination of TB bacilli to multiple
organs via macrophages and the bloodstream.
A. It is called miliary tuberculosis because it results in
the formation of thousands of small tubercles that
look like millet seeds in internal organs,
Miliary TB causes wasting
(weigh loss, loss of vigor)
and is fatal in 1-2 years.
host is tuberculin positive
Disease is contained; bacteria live
but are unable to replicate;
25% develop Ghon complex
host is tuberculin negative
Progressive systemic
disease and death
3. About 30% of hosts with
active untreated TB develop miliary tuberculosis |
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Term
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Definition
TB of tonsils, intestinal lymph nodes,
cervical lymph nodes (scrofula) and bones. It is caused
by ingestion of M. bovis or M. tuberculosis |
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Term
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Definition
the initial M. tuberculosis infection in
the lungs. It results in an arrested infection in 95% of
hosts; the other 5% develop progressive primary TB |
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Term
| Secondary (reactivation) TB |
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Definition
is the reestablishment of
active TB in the lungs after a period of dormancy which
can be short or long in duration depending on the state
of the host’s cellular immunity. About 10% of infected
hosts develop reactivation TB, usually within 2 years. |
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Term
| Diagnosis of Tuberculosis |
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Definition
Active TB is diagnosed by demonstrating the
presence of M. tuberculosis or M. bovis in a host’s
sputum or other clinical specimen by microbial
culture or other M. tuberculosis/bovis specific test.
A. Microbial culture of M. tuberculosis from sputum or
other lesion can take 3-6 weeks before visible growth is
observed because tubercle bacilli grow very slowly
The U.S. uses tuberculin skin testing as a screening
tool to identify potential cases of active TB.does not distinguish active TB from inactive or previous infection, or from BCG immunization.
Two TB skin tests are in widespread use, the Old
Tuberculin Tine Test and the Mantoux test.
A. The tine test employs a manufactured device that has
steel tines coated with tuberculin proteins.
B. The Mantoux test employs intradermal injection of a
purified tuberculin protein derivative called PPD.
C. A positive TB skin test produces induration (a hard
swelling) one cm or more in diameter at the test site. It
also causes redness but the *test is read by the induration*
Tuberculin-positive hosts are given a chest X-ray to determine if lesions are present in their lungs.
A. Ghon complexes are usually localized to the base and central areas of the lungs. Secondary TB lesions usually occur in apical areas and are more extensive.
B. Miliary TB of the lungs appears as small white lesions throughout both lungs |
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Term
| Treatment of Active Tuberculosis |
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Definition
long regimens with multiple anti-TB
drug cocktails (6 months in uncomplicated cases;
12-18 months or longer with advanced TB or drug resistant tubercle bacilli).
Drug-resistant tubercle bacilli quickly emerge if a
single anti-tubercular drug is given, so multi-drug
cocktails are given to prevent the emergence of
antibiotic resistant strains.
The recommended regimen for uncomplicated TB
cases is isoniazid, rifampin and pyrazinamide for 2
months, then isoniazid and rifampin for 4 months. |
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Term
| Mycobacterium avium-intracellulare |
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Definition
act as opportunistic pathogen in the most common cause of opportunistic Mycobacterium infection in AIDS patients in the United States
acquired by ingesting the
causative organisms in contaminated food or water.
B. Ingested mycobacteria initially infect Peyer’s patches in the
intestinal tract. They cause diarrhea and disseminate from
Peyer’s patches via lymphohematogenous spread to many
organs and tissues in the body.
C. These infections are difficult to treat because AIDS patients
are immunodeficient, few antibiotics are effective against
mycobacteria and the infections become widely |
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