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microbial diseases laboratory branch

Test Name

Mycobacterium tuberculosis Complex: Drug Susceptibility Testing, First-Line

Test ​​​​​M​​​e​th​o​​​d​​​olog​y​​​

​Phenotypic drug susceptibility testing of Mycobacterium tuberculosis complex at critical concentrations by BACTEC MGIT 960 system.​​ Routinely tested drugs: isoniazid (INH) 0.1 μg/ml, rifampin (RIF) 1 µg/ml, pyrazinamide (PZA) 100 µg/ml, and ethambutol (EMB) 5 µg/ml. Submitters may request the alternative first-line DST panel where moxifloxacin (MFX) 0.25 µg/ml is tested instead of EMB. ​​

Reflex Testing

​​​​If resistance to any of the first-line drugs (​except PZA) is detected, second-line drug susceptibility testing will be performed.

The default second-line drug panel includes amikacin (AMK), capreomycin (CAP), kanamycin (KAN), rifabutin (RFB), ethionamide (ETA), and MFX. If MFX testing was previously performed as part of alternative first-line DST and resistance to RIF, INH, or MFX was observed, EMB will be included in the second-line DST panel.

In addition, if resistance to INH at 0.1 μg/ml is detected, susceptibility testing to INH at 0.4 μg/ml will be performed.

Molecular detection of drug resistance by pyrosequencing may also be performed on cultures including mixed or contaminated cultures when there is known or suspected phenotypic drug resistance.

Pre-A​pproval Required​
​​No, unless:
​D​uplicate submission, i.e., samples from the same patient collected within 3 months from prior collection date.

Supp​lemental Information and Required Form(s)​
Barcode subm​ittal form 444 “Mycobacteriology-Drug Susceptibility Testing of MTBC (CA only)”  or instructions for using the MDL Lab Web Portal (ETOR) can be found at:  MDL Submission Instructions and Forms​.​​
​Indicate submitter’s test results on the submittal form.​​​
Required Specimen Type(s)

​Pure culture ​on solid or liquid media.
Slants (LJ/ 7H10) or liquid cultures (MGIT broth) are the preferred culture media for submission.

Minimum Volume Required
​Viable growth should be present on subculture.
​​1.0 mL minimum if broth submitted

Specimen Stability

​​​Room Temp: up to 4 weeks.
Refrigerated (2 – 8°C): up to 6 months.
Frozen: Subculture prior to submission.
If culture age exceeds above mentioned, subculture prior to submission and submit fresh culture
Rejection Criteria

  • ​​Samples with insufficient or conflicting labelling​​
  • ​Leaking samples
  • ​Isolates with no growth
  • ​Isolates that are nonviable
  • Mixed cultures
  • Specimen/sample types not meeting acceptance criteria​​
Storage/Transport Conditions

​Grow isolate under appropriate conditions and verify purity prior to shipping. Isolates may be stored refrigerated or at ambient temperature prior to shipping.​

Transport Medium,​
if applicable​​

​Not Applicable
Specimen Labeling

​Two identifiers, including patient full name, and at least one other identifier (specimen accession number, date of birth, medical record number).​​
Shipping Instructions and Specimen Handling Requirements

​​​Ship isolates at ambient temperature or with cold packs; do not freeze.

Follow the appropriate DOT/IATA approved shipping procedures. Suspected or confirmed MTBC cultures should be shipped as a Category A Infectious Substance, Affecting Humans (UN2814).

Ensure that culture isolates are sent in media flask or tubes containing a screw-top cap that is additionally sealed with parafilm or tape for additional protection against leaking. DO NOT send plate cultures.

Ship to:

California Depart​ment of Public Health​
Microbial Diseases Laboratory ​
ATTN:  TB Drug Susceptibility Testing Unit ​​
850 Marina Bay Parkway, Specimen Receiving Room B106
Richmond, CA  94804

Specimen Collection Instructions, if applicable

​​Not Applicable
Turnaround Time

​17 days​
Interferences & Limitations

​​Results may be delayed or unattainable if mixed culture is submitted.

Reference Range
​Not Applicable​
Additional Information
​​Isolates that are tested at MDL will be forwarded to the CDC if further characterization is needed or requested. 

MDL Point of Contact
​For questions regarding submissions, please email or call the MMPDS Section at (510) 412-3929​​

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