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Chapter 14: Mycobacterium


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What are the two species of mycobacterium?
Mycobacterium tuberculosis and Mycobacterium leprae
What are the two acid-fast staining bugs?
Mycobacteria and Nocardia
Mycobacteria - aerobes or anaerobes?
Obligate aerobes
Growth and pathogenesis of Mycobacterium tuberculosis?
Facultative intracellular growth - allows the bacteria to cruise through the lymphatics and blood. Eventual macrophage attack results in local destruction of tissue and caseous necrosis.
PPD? what does it detect?
Purified Protein Derivative. Detects whether a person has been exposed to/infected with tuberculosis, NOT necessarily active tuberculosis.
Describe primary tuberculosis? Transmission
Usually a subclinical lung infection. Transmitted via aerosolized droplet nuclei, which land in the middle and lower lung zones. Cell-mediated immunity walls off and suppresses the bacteria, which lie dormant.
Describe secondary tuberculosis? aka?
Aka reactivation TB. Infection can occur in any organ system seeded during the primary infection.
1. Pulmonary - most coomon
2. Pleural, pericardial infection
3. Lymph node infection
4. Kidney
5. Skeletal
6. Chronic arthritis of a joint
7. Subacute meningitis
8. Miliary tuberculosis
What is a Ghon focus?
A calcified tubercle in the middle or lower lung zone.
What is a Ghon complex?
A Ghon focus accompanied by perihilar lymph node calcified granulomas.
What is the general presentation of TB?
Chronic - weight loss, low-grade fever, symptoms related to the organ system infected. Often confused with cancer; one of the great imitators.
How can TB be diagnosed?
PPD skin test, chest Xray, and sputum acid-fast stain and culture.
What is the lifetime reactivation risk in patients exposed to TB? What is the ANNUAL reactivation risk in HIV patients?
10% for both.
What is Mycobacterium avium-intracellulare?
Usually only affects birds and other animals - but infects up to 50% of AIDS patients.
Leprosy involves which parts of the body?
The cooler areas - skin (except the armpit, grouin and perineum), the superficial nerves, eyes, nose, and testes.
What is the severest form of leprosy? Manifestations?
Lepromatous leprosy (LL) - no cell-mediated immune response can be mounted. Leonine facies (lion face), saddlenose deformity, internal testicular damage, loss of sensation in glove and stocking distribution.
What is tuberculoid leprosy?
Patients can mount a cell-mediated defense - milder and often self-limiting disease.
How is leprosy tested for?
Lepromin skin test - measures the ability of the host to mount a delayed hypersensitivity reaction against antigens of Mycobacterium leprae.

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