Mycobacteriology Laboratory Branch
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Drug susceptibility testing
Drug susceptibility testing is a difficult procedure to standardize,
and proficiency in performing these tests requires an understanding
of many elements, including the
- Origin of drug resistance and the criteria for resistance
- Potency and stability of drugs during laboratory manipulation
- Antimycobacterial activity of drugs when incorporated into different
media
- Reading, interpretation, and reporting of results
The MLB uses an indirect proportion method for testing M. tuberculosis
and other slow-growing mycobacteria to 11 drugs at 35°C on Middlebrook
7H10 agar. The test requires 1 month to complete. Growth on the
control medium is compared to the growth on the drug-containing
medium to determine susceptibility or resistance. When performed
properly, this method allows a quantitation of the proportion of
mutants resistant to a drug and can detect the 1% proportion of
drug- resistant mutants above which therapeutic failure is likely.
Slow growing mycobacteria are tested with the following drugs:
- Isoniazid
- Streptomycin
- Ciprofloxacin
- Capreomycin
- Kanamycin
- Pyrazinamide
- Cycloserine
- Ethambutol
- Rifampin
- Ethionamide
- Rifabutin
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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