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12 Cards in this Set

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  • Back
What are some characteristics of mycobacteria?
Obligate aerobes, acid fast bacilli, intracellular growth, and multiple drug resistance.
How are mycobacteria visualized under the light microscope?
Appear red with Zieghl Neelsen acid fast stain. Stain poorly with Gram stain. neither G+ or G-.
What is the principal dye in acid fast stain and what component of the cell wall does it bind?
Carbofuchsin binds to mycolic acid(long-chain fatty acid) which is present in abundance in the cell wall.
What other bacteria are acid fast?
Nocardia species are acid fast because their cell walls are also high in mycolic acid.
What 2 classic ancient diseases are caused by Mycobacteria?
Tbc(consumption) by M. tbc and leprosy(hansen's disease) by M. leprae.
What populations are most at risk for tbc?
Elderly persons, immunocompromised, HIV, transplant recipients and those from lower socioeconomic status.
What factor is responsible for the serpintine growth pattern seen with virulent strains of M. tbc?
Cord factor, only produced by virulent starins.
Sulfatides allow for the intracellular growth of M. tbc by what mechanism?
Sulfatides promote survival within macrophages by inhibiting phagosome-lysosome fusion and superoxide formation.
What is the main host defense against M. tbc?
Cell mediated immunity(CD4, T cells and macrophages.
Purified protein derivative is a skin test for tbc. How does it work?
Intradermally injected proteins from M. tbc iniate a local delayed type hypersensitivity reaction(type 4 in previously infected individuals).
What are the criteria for a positive PPD skin test?
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.
How is latent tbc infection detectyed and how is it treated?
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.