Test Methodology
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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.
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Reflex Testing
Criteria
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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.
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Pre-Approval Required
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No, unless:
Duplicate submission, i.e., samples from the same patient collected within 3 months from prior collection date.
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Supplemental Information and Required Form(s)
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Barcode submittal 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.
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Required Specimen Type(s)
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Pure culture on solid or liquid media.
Slants (LJ/ 7H10) or liquid cultures (MGIT broth) are the preferred culture media for submission.
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Minimum Volume Required
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Viable growth should be present on subculture.
1.0 mL minimum if broth submitted
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Specimen Stability
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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.
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Rejection Criteria
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- 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
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Storage/Transport Conditions
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Grow isolate under appropriate conditions and verify purity prior to shipping. Isolates may be stored refrigerated or at ambient temperature prior to shipping.
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Transport Medium,
if applicable
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Not Applicable
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Specimen Labeling
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Two identifiers, including patient full name, and at least one other identifier (specimen accession number, date of birth, medical record number).
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Shipping Instructions and Specimen Handling Requirements
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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 Department of Public Health
Microbial Diseases Laboratory
ATTN: TB Drug Susceptibility Testing Unit
850 Marina Bay Parkway, Specimen Receiving Room B106
Richmond, CA 94804
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Specimen Collection Instructions, if applicable
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Not Applicable
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Turnaround Time
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17 days
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Interferences & Limitations
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Results may be delayed or unattainable if mixed culture is submitted.
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Reference Range
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Not Applicable
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Additional Information
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The isolates will be forwarded to CDC if further characterization is needed.
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MDL Point of Contact
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For questions regarding submissions, please email CDPHTBDST@cdph.ca.gov or call the MMPDS Section at (510) 412-3929
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