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Test ID: MMLSG Antimicrobial Susceptibility, Acid-Fast Bacilli, Slowly Growing, Varies

Infectious

Reporting Name

Susc, AFB, Slowly Growing

Useful 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 (IDSA) 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

Varies


Ordering 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


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 unless identification of organism is provided.



Shipping Instructions


1. See Infectious Specimen Shipping Guidelines

2. Place specimen in a large infectious container (T146) and label as an etiologic agent/infectious substance.



Necessary Information


Specimen source and organism identification are required.



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 

Reference Values

Interpretive criteria for Mycobacterium avium-intracellulare complex

Antimicrobial agent

Minimum inhibitory concentration (MIC, mcg/mL) for each interpretation

 

S

I

R

Clarithromycin

≤8

16

≥32

Linezolid

≤8

16

≥32

Moxifloxacin

≤1

2

≥4

Amikacin (IV)

≤16

32

≥64

Amikacin (liposomal, inhaled)

≤64

-

≥128

 

Interpretative criteria for Mycobacterium kansasii and other slowly growing mycobacteria

Antimicrobial agent

MIC (mcg/mL) for each interpretation

 

S

I

R

Amikacin

≤16

32

≥64

Ciprofloxacin

≤1

2

≥4

Clarithromycin

≤8

16

≥32

Doxycycline

≤1

2-4

≥8

Linezolid

≤8

16

≥32

Minocycline

≤1

2-4

≥8

Moxifloxacin

≤1

2

≥4

Rifabutin

≤2

-

≥4

Rifampin

≤1

-

≥2

Trimethoprim/
Sulfamethoxazole

≤2/38

-

≥4/76

 

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. This test 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 antimicrobials listed below are included on the routine panel. Those marked with an "X" are routinely reported.

Organism

Antimicrobial agent

 

Amikacin

Clarithromycin

Clofazimine

Ciprofloxacin

Doxycycline

Linezolid

Minocycline

Moxifloxacin

Rifabutin

Rifampin

Streptomycin

Trimethoprim-sulfamethoxazole

Mycobacterium avium complex

X

X

X

 

 

X

 

X

 

 

 

 

Other slowly growing nontuberculous Mycobacterium species

X

X

X

X

X

X

X

X

X

X

 

X

 

 

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 Jul 7;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 Aug 14;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 Feb;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 Feb;55:122-124. doi: 10.1016/j.ijid.2016.12.027

Report Available

12 to 35 days

Method 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

Mayo Clinic Laboratories | Microbiology and Infectious Disease Catalog Additional Information:

mml-mycobacteria