Molecular Detection of Drug Resistance (MDDR) for Mycobacterium tuberculosis complex
Molecular-based antimicrobial susceptibility testing (AST) is a rapid DNA sequencing based platform aimed at the detection of genetic markers of drug resistance for Mycobacterium tuberculosis complex (MTBC). Results are available in hours as compared to weeks for conventional antimicrobial susceptibility testing.
Rapid molecular-based antimicrobial susceptibility testing using DNA pyrosequencing.
Molecular and growth-based susceptibility testing are automatically performed on MTBC isolated from each patient.
Submit isolates using the tuberculosis (TB) Category A carrier provided by the MSPHL in accordance with the Infectious Substance, Category A shipping guidelines.
Acceptable Specimen Type(s)
Submit a slant (L-J, Middlebrook, or Mitchison) or liquid broth culture (MGIT, VersaTREK, or MP).
Mixed or non-viable MTBC organism is acceptable; however, growth-based AST may not be available.
Test Request Form(s)
No MTBC amplification detected
No mutation detected
rpoB mutation present (Ser531Leu) - resistance to rifampin
rpoB mutation present (Phe514Phe) - silent mutation; does not confer resistance to rifampin
katG mutation present (Ser315Thr), and no inhA or ahpC mutation present - resistance to isoniazid
No katG or ahpC mutation present, and inhA mutation present (C-15T) - low-level isoniazid resistance
ahpC mutation present (G-10A) - resistance to isoniazid
gyrA mutation present (Asp94Gly) - resistance to fluoroquinolones
rrs mutation present (A1401G) - resistance to second-line injectable drugs (amikacin, kanamycin, capreomycin)
The wild-type amino acid, codon number and mutant amino acid will be reported when a mutation is present. Examples listed above are of the most common mutations within Missouri. Novel mutations detected by pyrosequencing will be reported with referenced literature.
Mutation present or not detected by DNA sequencing in the following targeted regions associated with drug resistance.
IS6110 - M. tuberculosis complex confirmation
rpoB (RRDR) - Rifampin
katG (Ser315 Codon) - Isoniazid
inhA (Promoter) - Isoniazid
ahpC (Promoter) - Isoniazid
gyrA (QRDR) - Fluoroquinolones
rrs (1400 Region) - Second-line injectable drugs (Amikacin, Kanamycin, Capreomycin)
No name or patient identifier on specimen
Specimen leaked during transport to the laboratory
Results are reported the same day of receipt for known TB isolates
An isolate with mutations present confirming multidrug-resistant TB (MDR-TB) or extensively drug resistant TB (XDR-TB) will automatically be submitted to the CDC for confirmation and second-line antimicrobial susceptibility testing.
Testing will automatically be repeated, or upon request, on MTBC isolated from patients who has been on three months of antitubercular therapy to determine if the patient has developed resistance.
The Association of State and Territorial Health Officials (ASTHO) recognized the use of a universal laboratory screening test for multidrug-resistant tuberculosis (MDR-TB); resistance to rifampin and isoniazid. Reflex testing is beneficial, as it allow the most rapid detection of MDR and XDR-TB patients.