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23 Cards in this Set
- Front
- Back
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How are atypical mycobacterium infections differentiated from the MTB?
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PPD is + (at high concentration--250 vs 5), but the infection is subclinical, usually a pneumonia, or lymphadenitis in children.
Some colonies have pigment (yellow or orange). |
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Why do mycobacterium stain acid fast? What other organisms stain acid fast?
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High lipid content in the cell walls hold fast to the red stain and do not decolorize with acid-alcohol.
Mycobacteria and Nocardia are acid fast and appear RED. |
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What is BCG? What are the pros and cons of its use?
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bacillus Calmette-Guerin vaccine for TB.
Pros: Gives at least partial immunity to children and adults Cons: Effectiveness is debated. Gives a +PPD. Ruins screening tool. |
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What is the mycobacterium screening test?
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PPD
Purified Protein Derivative is injected just below the skin to induce delayed type hypersensitivity in infected patients. + for active or latent TB, and for atypical mycobacterium. |
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Relate hypersensitivity to mycobacterium resistance.
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There is no relation. A delayed hypersensitivity only shows that an immune response is present. It does not confer immunity or resistance. It is a sign of existing or previous disease (except for BCGs)
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Relate hypersensitivity to pathogenesis in MTB.
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Delayed hypersensitivity is the cause of lung tissue damage in MTB. Sensitized T-cells respond and recruit macrophages that destroy the lung tissue where the bug is hiding. This causes caseous necrosis that can become fibrotic and calcific.
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Describe the virulence factors of MTB.
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1. Mycolic acid cell walls
2. Cord factor: inhibits PMNs and damages mitochondria. Seen to cause rapid weight loss. 3. Sulfatides: resemble cord factor, inhibit phagosome from fusing with the lysosome. This allows intracellular survival. 4. Wax D: activates the protective cellular mechanism that causes DTH. |
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Describe the dose reaction to tuberculin.
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If positive at 5UT: past or present infection
If negative at 5UT and + at 250UT: Non-TB infection. Retest with something more specific. If negative at 250UT: negative and susceptible or anergic (Think HIV). |
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How fast can isolation and acid-fast stain be done?
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Very slow grower (days?)
PPD (48hrs) |
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What is leprosy diagnosed?
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Lepromin skin test (PPD), more prognostic than diagnostic.
Cannot be cultured. |
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What is the immune statue if the host is showing lepromatous leprosy?
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Host has no DTH, no macrophage response possibly due to defective T suppressors blocking T response.
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What is the immune status if the host is showing tuberculoid leprosy?
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Host has a DTH. Immune system might clear the bacteria. Pathology is limited.
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Why is amphotericin B not work against Norcardia?
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Polyenes target the ergosterols in fungal cell walls. Norcardia does not have ergosterols
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How are norcardia similar to mycobacterium?
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They are acid-fast. Norcardia can be distinguished because it has aerial hyphae and is only weakly acid fast.
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How is norcardiosis diagnosed?
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Multiple sputum samples. It is relatively easy to collect because it is widely distributed. Accurate identification is done with DNA/RNA PCR.
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Describe the staining characteristics of Nocardia.
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Gram +
Partially acid-fast |
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What disease is caused by nocardia?
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Pulmonary (TB-like) or cutaneous lesions
Can metastasize to brain. |
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What is the source of nocardia infection?
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Soil
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What are the causative agent for listeriosis and routes of infection?
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Listeria monocytogenes from:
Raw milk products from infected cow. Vaginally during birth Transplacental infection of baby from infected mom |
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Who is most at risk to develop listeriosis?
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Young, old, and immunocompromised
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What diseases are caused by listeria?
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Meningitis
Meningoencephalitis with septicemia CNS infections Febrile gastroenteritis |
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How does listeria avoid antibody-mediated killing?
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Listeriolysin O allows listeria to escape the phagolysosomes of macrophages. Then the bacteria replicates in the macrophage. Humoral immunity does nothing to control infection.
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What are the essential virulence factors for listeria?
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Listeriolysin O
Phospholipase A2 ActA: allows intracellular movement along actin cytostructure of macrophage. |
