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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 LB uses an indirect proportion method for testing M. tuberculosis complex mycobacteria to 12 drugs at 35C 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.

M. tuberculosis complex are tested by this method with the following drugs:

  • Isoniazid
  • Rifampin
  • Ethambutol
  • Ciprofloxacin
  • Ofloxacin
  • Streptomycin
  • Kanamycin
  • Capreomycin
  • Amikacin
  • Rifabutin
  • Ethionamide
  • Para-aminosalicylic acid (PAS)

Pyrazinamide is tested by the MGIT 960 method.  

Additionally, bedaquiline testing is available upon request [PDF 108 KB]

Additional Resources