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microbial diseases laboratory BRANCh

Test Name

Mycobacterium tuberculosis Complex: Drug Susceptibility Testing, Second 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.​​

​Tested drugs: amikacin (AMK) 1.5 µg/ml, capreomycin (CAP) 3 µg/ml, kanamycin (KAN) 3.5 μg/mL, rifabutin (RFB) 0.5 μg/mL, ethionamide (ETA) 5 µg/ml, and moxifloxacin (MFX) 0.25 µg/ml. If MFX testing was previously performed as part of alternative first-line DST, it will not be included in second line panel.

Susceptibility to MFX at 0.25 μg/ml predicts susceptibility to levofloxacin (LEV) as well; however, LEV can be tested instead of MFX upon request. MFX MIC may be requested by the submitter, but will only be performed after MFX resistance at 0.25 ug/mL is observed.

Second line DST for either streptomycin or ethambutol (if not included with first line panel) is available upon request only.

Reflex Testing

​When resistance to MFX at 0.25 µg/ml is detected, MFX MIC testing can be performed at 0.5, 1.0, 2.0, and 3.0 μg/ml upon request.

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 Su​bmission 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
​​The isolates will be forwarded to CDC if further characterization is needed. ​

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

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