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

Useful For Suggests clinical disorders or settings where the test may be helpful

Determination of resistance of slowly growing mycobacteria to antimicrobial agents

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

There are currently more than 60 recognized, validated species of slowly growing nontuberculous mycobacteria and they are associated with a variety of infections including pulmonary, extrapulmonary, 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.

 

The antimicrobial agents tested for each species or group are as follows:

 

Mycobacterium avium Complex:

Clarithromycin is tested and is the CLSI recommended primary agent. Moxifloxacin and linezolid are tested and are secondary agents with recommended CLSI breakpoints. Other recognized secondary drugs tested and reported without CLSI interpretive breakpoints are amikacin, ethambutol, rifampin, rifabutin, and streptomycin.

 

Mycobacterium kansasii, Mycobacterium malmoense, Mycobacterium simiae, Mycobacterium terrae, and Mycobacterium xenopi:

Clarithromycin and rifampin are tested and are the CLSI recommended primary agents. Amikacin, ciprofloxacin, ethambutol, linezolid, moxifloxacin, rifabutin, and trimethoprim/sulfamethoxazole are tested and are secondary agents with recommended CLSI breakpoints. Isoniazid and streptomycin are tested and are secondary agents per CLSI but do not have recommended breakpoints. Mycobacterium malmoense can be difficult to grow in the test medium so some isolates may not be amenable to testing.

 

Mycobacterium marinum:

CLSI recommended agents tested are amikacin, ciprofloxacin, clarithromycin, doxycycline/minocycline, ethambutol, moxifloxacin, rifabutin, rifampin, and trimethoprim/sulfamethoxazole.

 

Mycobacterium gordonae:

Mycobacterium gordonae is frequently encountered in the environment and in clinical laboratories but is almost always considered nonpathogenic; therefore, antimicrobial susceptibility testing for Mycobacterium gordonae is performed by specific request only.

 

Other slowly growing mycobacterial species:

All other slowly growing mycobacterial species will be tested against the Mycobacterium kansasii panel of drugs and minimum inhibitory concentration values will be provided using the Mycobacterium kansasii interpretative criteria. The extremely fastidious slowly growing mycobacteria (Mycobacterium genavense and Mycobacterium haemophilum) will not be tested.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Interpretive Criteria for Mycobacterium avium-intracellulare complex

Antimicrobial agent

MIC (mcg/mL) for each interpretation

 

S

I

R

Clarithromycin

< or =8

16        

> or =32

Linezolid

< or =8

16        

> or =32    

Moxifloxacin

< or =1

 2         

> or =4

Amikacin

No Interpretations available

Ciprofloxacin

No Interpretations available

Ethambutol

No Interpretations available

Ethionamide

No Interpretations available

Rifabutin

No Interpretations available

Rifampin

No Interpretations available

Streptomycin

No Interpretations available

 

Interpretative criteria for  Mycobacterium kansasii and other slowly growing mycobacteria

Antimicrobial agent

MIC (mcg/mL) for each interpretation

 

S

R

Amikacin

< or =32

>32

Ciprofloxacin

< or =2

>2

Clarithromycin

< or =16

>16

Ethambutol

< or =4

>4

Isoniazid

No Interpretations available

Linezolid

< or =16

>16

Moxifloxacin

< or =2

>2

Rifabutin

< or =2

>2

Rifampin

< or =1

>1

Streptomycin

No Interpretations available

Trimethoprim/
Sulfamethoxazole

< or =2/38

>2/38

 

Interpretative criteria for Mycobacterium marinum

Antimicrobial agent

MIC (mcg/mL) for each interpretation

 

S

R

Amikacin

< or =32

>32

Ciprofloxacin

< or =2

>2

Clarithromycin

< or =16

>16

Doxycycline

< or =4

>4

Ethambutol

< or =4

>4

Moxifloxacin

< or =2

>2

Rifabutin

< or =2

>2

Rifampin

< or =1

>1

Trimethoprim/Sulfamethoxazole

< or =2/38

>2/38

 

Interpretation Provides information to assist in interpretation of the test results

Results are reported as the minimum inhibitory concentration in micrograms/mL.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Richter E, Brown-Elliott BA, Wallace RJ Jr: Mycobacterium: laboratory characteristics of slowly growing mycobacteria. In Manual of Clinical Microbiology. Tenth edition. Edited by J Versalovic, KC Carroll, G Funke, et al. ASM Press, Washington, DC, 2011, pp 503-524

2. Tortoli E: Impact of genotypic studies on mycobacterial taxonomy: the new mycobacteria of the 1990s. Clin Microbiol Rev 2003 Apr;16(2):319-354

3. Griffith DE, Aksamit T, Brown-Elliott BA, et al: An Official ATS/IDSA Statement: Diagnosis, Treatment, and Prevention of Nontuberculous Mycobacterial Diseases. American Thoracic Society 2007

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test