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12 Cards in this Set
- Front
- Back
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What are some characteristics of mycobacteria?
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Obligate aerobes, acid fast bacilli, intracellular growth, and multiple drug resistance.
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How are mycobacteria visualized under the light microscope?
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Appear red with Zieghl Neelsen acid fast stain. Stain poorly with Gram stain. neither G+ or G-.
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What is the principal dye in acid fast stain and what component of the cell wall does it bind?
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Carbofuchsin binds to mycolic acid(long-chain fatty acid) which is present in abundance in the cell wall.
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What other bacteria are acid fast?
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Nocardia species are acid fast because their cell walls are also high in mycolic acid.
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What 2 classic ancient diseases are caused by Mycobacteria?
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Tbc(consumption) by M. tbc and leprosy(hansen's disease) by M. leprae.
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What populations are most at risk for tbc?
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Elderly persons, immunocompromised, HIV, transplant recipients and those from lower socioeconomic status.
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What factor is responsible for the serpintine growth pattern seen with virulent strains of M. tbc?
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Cord factor, only produced by virulent starins.
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Sulfatides allow for the intracellular growth of M. tbc by what mechanism?
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Sulfatides promote survival within macrophages by inhibiting phagosome-lysosome fusion and superoxide formation.
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What is the main host defense against M. tbc?
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Cell mediated immunity(CD4, T cells and macrophages.
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Purified protein derivative is a skin test for tbc. How does it work?
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Intradermally injected proteins from M. tbc iniate a local delayed type hypersensitivity reaction(type 4 in previously infected individuals).
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What are the criteria for a positive PPD skin test?
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A positive test is defined based on the size of the red, raised induration after 48 hrs:>15mm for persons with no known exposure,>10mm in high risk patients(health care workers included),>5mm in HIV patients or those with recent known exposure.
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How is latent tbc infection detectyed and how is it treated?
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Latent infection is conversion to positive PPD with no signs or symptoms of active disease and no signs of disease on chest X-ray. First line treatment is 9 months of Isoniazid.
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