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Interpretive Handbook

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Test 81601 :
Antimicrobial Susceptibility, Acid-Fast Bacilli, Rapidly Growing

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

The rapidly growing species of mycobacteria (eg, Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium chelonae, Mycobacterium abscessus, and Mycobacterium mucogenicum) are seen with increasing frequency as causes of infection. Some examples of infections caused by this group of mycobacteria are empyema, subcutaneous abscess, cutaneous ulcerative and nodular lesions, peritonitis, endometriosis, bacteremia, keratitis, and urinary tract, prosthetic joint, wound, and disseminated infections.

 

Rapidly growing mycobacteria differ from other species of mycobacteria by their growth rates, metabolic properties, and antimicrobial susceptibility profiles. Most species are susceptible to some of the traditional antimycobacterial agents, but rapidly growing species may exhibit resistance to certain antimycobacterial agents. In contrast, they often are susceptible to several of the antibacterial agents used to treat common bacterial infections. Therefore, the antimicrobial susceptibility profile of an organism within this group varies depending on the species. Isolates of Mycobacterium fortuitum and Mycobacterium peregrinum generally exhibit susceptibility to amikacin, ciprofloxacin, clarithromycin, imipenem, and sulfamethoxazole; while isolates of Mycobacterium chelonae are generally susceptible to amikacin and clarithromycin only. Mycobacterium abscessus is usually susceptibility to clarithromycin, imipenem, and amikacin.

 

Antimicrobials tested in this assay are amikacin, cefoxitin, ciprofloxacin, clarithromycin, doxycycline, imipenem, tobramycin, trimethoprim/sulfamethoxazole, linezolid, moxifloxacin, and tigecycline.

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

Determination of resistance of rapidly growing mycobacteria to antimicrobial agents

Interpretation Provides information to assist in interpretation of the test results

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

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.

 
Antimicrobial

Susceptible (mcg/mL)

Intermediate (mcg/mL)

Resistant (mcg/mL)

Amikacin

< or =16

32

> or =64

Cefoxitin

< or =16

32-64

> or =128

Ciprofloxacin

< or =1.0

2.0

> or =4.0

Clarithromycin

< or =2.0

4.0

> or =8.0

Doxycycline

< or =1.0

2.0-8.0

> or =16

Imipenem

< or =4.0

8.0

> or =16

Tobramycin

< or =4.0

8.0

> or =16

Linezolid

< or =8

16

> or =32

Trimethoprim/Sulfamethoxazole

< or =2/38

-

> or =4/76

Moxifloxacin

< or =1.0

2

> or =4.0

Tigecycline

No interpretations available

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

1. Brown-Elliott BA, Wallace RJ Jr.: Clinical and taxonomic status of pathogenic nonpigmented or late-pigmenting rapidly growing mycobacteria. Clin Microbiol Rev 2002 October;15:716-746

2. Colombo RE, Olivier KN: Diagnosis and treatment of infections caused by rapidly growing mycobacteria. Semin Respir Crit Care Med 2008 October;29:577-588


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