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HelpTest ID: MMLSG Antimicrobial Susceptibility, Acid-Fast Bacilli, Slowly Growing, Varies
Infectious
Reporting Name
Susc, AFB, Slowly GrowingUseful For
Determination of resistance of slowly growing mycobacteria to antimicrobial agents
Additional Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| RSLG | Susceptibility Slow Grower | No, (Bill Only) | Yes |
Testing Algorithm
When this test is ordered, susceptibility for slow growers will be performed at an additional charge. Antimicrobials are tested and reported using the Clinical and Laboratory Standards Institute (CLSI) guidelines.(1,2)
Antimicrobials tested for Mycobacterium avium complex (MAC): amikacin, clarithromycin, clofazimine, linezolid, and moxifloxacin. Per the CLSI standards set in document M24 for susceptibility testing of M avium complex, Minimum inhibitory concentration (MIC) data for ethambutol, rifampin, and rifabutin have shown poor correlation with clinical response.(1,2) Therefore, although these drugs are in the recommended Infectious Diseases Society of America treatment regimen for MAC, breakpoints for these agents that separate susceptible from resistant strains cannot be determined.(3,4) Reporting of MICs for these drugs is not recommended for use in patient care. Synergy testing for nontuberculous mycobacteria has also not been standardized and its value is unclear at this time. For these reasons, ethambutol, rifampin, rifabutin and combinations of these drugs will not be tested or reported. M avium complex isolates will not be forwarded to other institutions for susceptibility testing of rifampin, rifabutin, ethambutol or synergy testing since this practice is not recommended by the CLSI nor the IDSA.(5,6) An Infectious Diseases expert with experience in difficult or refractory MAC cases should be consulted since in vitro MIC values are not useful for these drugs.
Antimicrobials tested for all other slowly growing Mycobacterium species: amikacin, clarithromycin, clofazimine, ciprofloxacin, doxycycline, linezolid, minocycline, moxifloxacin, rifabutin, rifampin, and trimethoprim /sulfamethoxazole. Interpretive criteria are provided according to the CLSI standards.(1,2)
Clofazimine interpretive criterion is not available.
Specimen Type
VariesOrdering Guidance
For Mycobacterium tuberculosis complex, see TB1LN / Antimicrobial Susceptibility, Mycobacterium tuberculosis Complex, First Line, Varies and TBPZA / Susceptibility, Mycobacterium tuberculosis Complex, Pyrazinamide, Varies.
Additional Testing Requirements
If organism identification is not provided, CTB / Mycobacteria and Nocardia Culture, Varies or CTBID / Culture Referred for Identification, Mycobacterium and Nocardia, Varies must also be ordered and will be charged separately.
Shipping Instructions
1. For shipping information see Infectious Specimen Shipping Guidelines.
2. Place specimen in a large infectious container and label as an etiologic agent/infectious substance.
Necessary Information
1. Specimen source is required.
2. Organism identification is required unless either CTB / Mycobacteria and Nocardia Culture, Varies or CTBID / Culture Referred for Identification, Mycobacterium and Nocardia, Varies is also ordered.
Specimen Required
Specimen Type: Organism
Supplies: Infectious Container, Large (T146)
Container/Tube: Middlebrook 7H10 agar slant or other appropriate media
Specimen Volume: Isolate
Collection Instructions: Organism must be in pure culture, actively growing.
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Ambient (preferred) | ||
| Refrigerated | |||
Special Instructions
Reference Values
Interpretive criteria and reporting guidelines are followed using the Clinical Laboratory Standards Institute (CLSI) M24S document.
Day(s) Performed
Varies
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
87186
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MMLSG | Susc, AFB, Slowly Growing | 29579-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| MMLSG | Susc, AFB, Slowly Growing | 29579-0 |
Clinical Information
The slowly growing nontuberculous mycobacteria are associated with a variety of infections including pulmonary, extra-pulmonary, and disseminated disease.
Slowly growing mycobacteria differ from the rapidly growing mycobacteria and Mycobacterium tuberculosis complex by their growth rates, metabolic properties, and antimicrobial susceptibility profiles. The antimicrobial susceptibility profile of an organism within this group varies depending on the species and is performed according to the Clinical and Laboratory Standards Institute (CLSI) guideline for slowly growing mycobacteria.(1,2)
The extremely fastidious slowly growing mycobacteria (Mycobacterium genavense and Mycobacterium haemophilum) will not be tested. Mycobacterium malmoense can be difficult to grow in the test medium so some isolates may not be amenable to testing.
Mycobacterium xenopi requires incubation at a higher temperature and may require extended incubation times.
Mycobacterium gordonae is frequently encountered in the environment and in clinical laboratories but is almost always considered nonpathogenic; therefore, antimicrobial susceptibility testing for M gordonae is performed by specific request only.
Interpretation
Results are reported as the minimum inhibitory concentration in micrograms/mL.
Clinical Reference
1. CLSI: Susceptibility Testing of Mycobacteria, Nocardia spp., and Other Aerobic Actinomycetes. 3rd ed. CLSI standard M24. Clinical and Laboratory Standards Institute; 2018
2. CLSI: Performance Standards for Susceptibility Testing of Mycobacteria, Nocardia spp., and Other Aerobic Actinomycetes. CLSI supplement M62. Clinical and Laboratory Standards Institute; 2018
3. Daley CL, Iaccarino JM, Lange C, et al. Treatment of nontuberculous mycobacterial pulmonary disease: an official ATS/ERS/ESCMID/IDSA clinical practice guideline. Eur Respir J. 2020;56(1):2000535. doi:10.1183/13993003.00535-2020
4. Daley CL, Iaccarino JM, Lange C, et al. Treatment of nontuberculous mycobacterial pulmonary disease: An official ATS/ERS/ESCMID/IDSA clinical practice guideline. Clin Infect Dis. 2020;71(4):e1-e36. doi:10.1093/cid/ciaa241
5. Griffith DE, Winthrop KL. You gotta make me see, what does it mean to have an MIC?. Chest. 2021;159(2):462-464. doi:10.1016/j.chest.2020.11.007
6. Schon T, Chryssanthou E. Minimum inhibitory concentration distributions for Mycobacterium avium complex-towards evidence-based susceptibility breakpoints. Int J Infect Dis. 2017;55:122-124. doi:10.1016/j.ijid.2016.12.027
Report Available
12 to 35 daysMethod Name
Microtiter Broth Dilution
Forms
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.
Specimen Minimum Volume
See Specimen Required
mml-mycobacteria