Diagnosis of multidrug resistant

diagnosis of multi drug resistant tuberculosis

Diagnosis of MDR-TB requires that Mycobacterium tuberculosis bacteria be detected as the causative organism and resistance to anti-TB drugs determined.

This is carried out by isolating the bacteria by culture and conducting drug susceptibility testing (DST) using solid or liquid media or by performing a WHO endorsed molecular test to detect TB DNA and mutations associated with resistance.

• phenotypic indirect drug susceptibility testing
  • drug susceptibility testing is performed on cultured isolates of M. tuberculosis
  • culture require prolonged lengths of time hence require prolonged lengths of time
• phenotypic direct drug susceptibility testing
  • testing directly from a clinical sample (most commonly a sputum specimen)
  • due to the rapid, non-commercial, and low cost nature it is appropriate for resource constrained settings with a high burden of tuberculosis
• genotypic drug susceptibility testing
  • test for the presence of known resistance mutations associated with multidrug resistant tuberculosis.
  • two types of geneotypic assay have been endorsed by WHO:
    • molecular beacon assays
    • line probe hybridisation assays.

All patients diagnosed with MDR-TB should preferably be tested for XDR-TB (2)

Reference:

• (1) Millard J, Ugarte-Gil C, Moore DA. Multidrug resistant tuberculosis. BMJ. 2015;350:h882.
• (2) World Health Organization (WHO) 2014. Companion handbook to the WHO guidelines for the programmatic management of drug-resistant tuberculosis