TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

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

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

Determination of resistance of slowly growing mycobacteria to antimicrobial agents

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

When this test is ordered, Susceptibility Slow Grower will be performed and charged.

 

Antimicrobials for Mycobacterium avium complex: amikacin, clarithromycin, ethambutol, linezolid, moxifloxacin, rifabutin, rifampin, and streptomycin.

 

Antimicrobials for all other slowly growing Mycobacterium species: amikacin, clarithromycin, ciprofloxacin, doxycycline, linezolid, moxifloxacin, rifabutin, rifampin, trimethoprim and sulfamethoxazole.

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

The slowly growing nontuberculous mycobacteria 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 and amikacin are tested and are the CLSI recommended primary agents. Moxifloxacin and linezolid are tested and are secondary agents with CLSI breakpoints. Other recognized secondary drugs tested and reported without CLSI interpretive breakpoints are ethambutol, rifampin, rifabutin, and streptomycin. The in vivo effectiveness of moxifloxacin and linezolid for Mycobacterium avium complex (MAC) disease is unproven.

 

M kansasii: Clarithromycin and rifampin are tested and are the CLSI recommended primary agents. Amikacin, ciprofloxacin, linezolid, moxifloxacin, rifabutin, and trimethoprim/sulfamethoxazole are tested and are secondary agents with recommended CLSI breakpoints.  

 

Other slowly growing mycobacterial species:

All other slowly growing mycobacterial species will be tested against the M kansasii panel of drugs and minimum inhibitory concentration values will be provided using the CLSI interpretative criteria for slowly growing mycobacteria other than M avium complex and M kansasii. The extremely fastidious slowly growing mycobacteria (M genavense and M haemophilum) will not be tested. M malmoense can be difficult to grow in the test medium so some isolates may not be amenable to testing.

 

M gordonae:

M 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.

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 (IV)

< or =16

32

> or =64

Amikacin (liposomal, inhaled)

< or =64

-

> or =128

Ethambutol

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

I

R

Amikacin

< or =16

32

> or =64

Ciprofloxacin

< or =1

2

> or =4

Clarithromycin

< or =8

16

> or =32

Doxycycline

< or =1

2-4

> or =8

Linezolid

< or =8

16

> or =32

Moxifloxacin

< or =1

2

> or =4

Rifabutin

< or =2

-

> or =4

Rifampin

< or =1

-

> or =2

Trimethoprim/
Sulfamethoxazole

< or =2/38

-

> or =4/76

 

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 Recommendations for in-depth reading of a clinical nature

1. Caulfield AJ, Richter E, Brown-Elliott BA, et al: Mycobacterium: laboratory characteristics of slowly growing mycobacteria other than Mycobacterium tuberculosis. In Manual of Clinical Microbiology. Twelfth edition. Edited by KC Carroll, MA Pfaller, ML Landry, et al. ASM Press, Washington, DC, 2019, pp 595-611

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. Am J Respir Crit Care Med 2007 Feb 15;175(4):367-416

Special Instructions Library of PDFs including pertinent information and forms related to the test