Rapidly-growing Mycobacterium Susceptibility−Broth Dilution

CPT: 87186
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Test Details


  • M abscessus Susceptibility Testing
  • M chelonae Susceptibility Testing
  • M fortuitum Complex Susceptibility Testing
  • AFB Susceptibility Testing
  • Rapid-grower Susceptibility Testing

Test Includes

Susceptibility testing for amikacin, cefoxitin, ciprofloxacin, clarithromycin, imipenem (M fortuitum, M immunogenum, M smegmatis only), linezolid, minocycline, sulfamethoxazole-trimethoprim, and tobramycin (M chelonae only). MIC values will be reported with CLSI interpretive comments.


Determine the susceptibility of rapidly-growing mycobacterial isolates to a profile of antimycobacterial agents. Interpretive categories include the following.

Susceptible: This category implies that an infection due to the strain may be appropriately treated with the dosage of the recommended agent unless otherwise contraindicated.

Intermediate: Susceptibility is not certain since the available data does not permit categorization as either susceptible or resistant.

Resistant: Strains falling in this category are not inhibited by the usually achievable systemic concentration of the agent with normal dosage schedules and/or fall in the range where specific microbial resistance mechanisms are likely, and/or clinical efficacy has not been reliable in treatment studies.


Susceptibilities cannot be reported if the organism fails to grow in the test medium. Susceptibilities cannot be performed on mixed cultures. An organism identification is required prior to reporting susceptibility results. Imipenem results will only be reported for M fortuitum group, M smegmatis group, and M mucogenicum isolates.1 MICs for imipenem with other rapid growers (ie, M chelonae, M abscessus, M immunogenum) are problematic due to lack of reproducibility and, therefore, will not be reported. In vitro susceptibility studies reveal that tobramycin is the most active aminoglycoside for M chelonae. The recommendation is that tobramycin be reported for M chelonae only.1

Results of this test are labeled for research purposes only by the assay's manufacturer. The performance characteristics of this assay have not been established by the manufacturer. The result should not be used for treatment or for diagnostic purposes without confirmation of the diagnosis by another medically established diagnostic product or procedure. The performance characteristics were determined by LabCorp.


Sensititre® broth microdilution (MIC)

Additional Information

Failure to take all drugs in a multidrug regimen can lead to a shift toward resistant organisms and treatment failure.2

M fortuitum isolates are susceptible in vitro to multiple antimicrobial drugs and the clinical response to therapeutic agents appears to closely parallel the in vitro susceptibility patterns; however, this observation has not been evaluated by randomized controlled trials.3

M abscessus has limited in vitro susceptibility to any agent and clinical response in the treatment of pulmonary disease. There does appear, however, a correlation for M abscessus between in vitro susceptibility and clinical response for skin and soft tissue infections, although this has not been evaluated by randomized controlled trials.3

Few data are available to validate susceptibility testing as a guide for choosing antibiotics. Until the relationship between in vitro susceptibility testing and the clinical response to antimicrobial drugs is better understood and clarified, the clinician should use in vitro susceptibility data with an awareness of the limitations and that the disease may not be eradicated in a particular patient with therapy based on those results.3

Test results are not intended to be used as the sole means for patient management.

Extended incubation for up to 14 days will occur to evaluate the organism for inducible macrolide resistance.

Specimen Requirements


Rapidly-growing mycobacteria isolated from a primary clinical specimen, on a submitted AFB conventional solid medium, or an AFB broth medium


Pure culture isolate on an AFB conventional solid medium or a minimum of 1 mL of AFB broth medium


Conventional or broth medium, tightly sealed, in etiologic agent packaging

Storage Instructions

Maintain media at room temperature.

Causes for Rejection

Specimen received in leaking or in broken transport tube or vial; specimen received in expired transport medium; mixed culture; unlabeled culture or name discrepancy between specimen and request label

Clinical Information


1. Clinical and Laboratory Standards Institute (CLSI). Susceptibility Testing of Mycobacteria. Nocardia, and Other Aerobic Actinomycetes. Approved Standard. Vol 23, No 18. Villanova, Pa: CLSI, 2003, Document M24-A.
2. Wolinsky E. Mycobacterial diseases other than tuberculosis. Clin Infect Dis. 1992; 15(1):1-10.1617048
3. An Official ATS/IDSA Statement: Diagnosis, Treatment, and Prevention of Nontuberculous Mycobacterial Diseases. Am J Respir Crit Care Med. 2007; 175:367-416.17277290


Brown BA, Wallace RJ Jr, Onyi GO, De Rosas V, Wallace RJ 3rd. Activities of four macrolides, including clarithromycin, against Mycobacterium fortuitum,Mycobacterium chelonae, and M chelonae-like organisms. Antimicrob Agents Chemother. 1992 Jan; 36(1):180-184.1317144
Dalovisio JR, Pankey GA, Wallace RJ, et al. Clinical usefulness of amikacin and doxycycline in the treatment of infection due to Mycobacterium fortuitum and Mycobacterium chelonei.Rev Infect Dis. 1981; 3(5):1068-1074.7339806
Heifets L. Drug Susceptibility in the Chemotherapy of Mycobacterial Infections. Boca Raton, Fla: CRC Press;1991.
Heifets L. Qualitative and quantitative drug susceptibility tests in mycobacteriology. Am Rev Respir Dis. 1988; 137(5):1217-1222.3195815
Nash KA, Andini N, Zhang Y, Brown-Elliott BA, Wallace RJ Jr. Intrinsic macrolide resistance in rapidly growing mycobacteria. Antimicrob Agents Chemother. 2006; 50(10):34.17005837
Swenson JM, Thornsberry C, Silcox VA. Rapidly growing mycobacteria: Testing of susceptibility to 34 antimicrobial agents by broth microdilution. Antimicrob Agents Chemother. 1982; 22(2):186-192.6927280
Swenson JM, Wallace RJ Jr, Silcox VA, et al. Antimicrobial susceptibility of five subgroups of Mycobacterium fortuitum and Mycobacterium chelonae.Antimicrob Agents Chemother. 1985; 28(6):807-811.4083863
Wallace RJ Jr, Bedsole G, Sumter G, et al. Activities of ciprofloxacin and ofloxacin against rapidly growing mycobacteria with demonstration of acquired resistance following single-drug therapy. Antimicrob Agents Chemother. 1990; 34(1):65-70.2327761
Wallace RJ Jr, Brown BA, Onyi GO. Skin, soft tissue, and bone infections due to Mycobacterium chelonae (chelonae): Importance of prior corticosteroid therapy, frequency of disseminated infections, and resistance to oral antimicrobials other than clarithromycin. J Infect Dis. 1982; 166(2):405-412.1386098
Wallace RJ Jr, Brown BA, Onyi GO. Susceptibilities of Mycobacterium fortuitum biovar. fortuitum and the two subgroups of Mycobacterium chelonae to imipenem, cefmetazole, cefoxitin, and amoxicillin-clavulanic acid. Antimicrob Agents Chemother. 1991 Apr; 35(4):773-775.2069387
Wallace RJ Jr, Brown-Elliott BA, Ward SC, et al. Activities of linezolid against rapidly growing mycobacteria. Antimicrob Agents Chemother. 2001; 45(3):764-767.11181357
Wallace RJ Jr, Swenson JM, Silcox VA, et al. Treatment of nonpulmonary infections due to Mycobacterium fortuitum and Mycobacterium chelonei on the basis of in vitro susceptibilities. J Infect Dis. 1985; 152(3):500-514.3875667
Wallace RJ Jr, Swenson JM, Silcox VA, et al. Spectrum of disease due to rapidly growing mycobacteria. Rev Infect Dis. 1983; 5(4):657-679.6353528
Wallace RJ Jr, Tanner D, Brennan PJ, et al. Clinical trial of clarithromycin for cutaneous (disseminated) infection due to Mycobacterium chelonae.Ann Intern Med. 1993; 119(6):482-486.8357113
Wallace RJ Jr. The clinical presentation, diagnosis, and therapy of cutaneous and pulmonary infections due to the rapidly growing mycobacteria Mycobacterium fortuitum and Mycobacterium chelonae.Clin Chest Med. 1989; 10(3):419-429.2673650
Woods GL, Bergmann JS, Witebsky FG, et al. Multisite reproducibility of results obtained by the broth microdilution method for susceptibility testing of Mycobacterium abscessus,Mycobacterium chelonae, and Mycobacterium fortuitum.J Clin Microbiol, 1999; 37(6):1676-1682.10325306


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
182915 Rapid Grower Broth Suscep. 998563 Trimethoprim/Sulfa 516-5
182915 Rapid Grower Broth Suscep. 182862 Please note: N/A
182915 Rapid Grower Broth Suscep. 182916 Organism ID 40699-1
182915 Rapid Grower Broth Suscep. 998565 Amikacin 12-5
182915 Rapid Grower Broth Suscep. 998558 Cefoxitin 116-4
182915 Rapid Grower Broth Suscep. 998566 Ciprofloxacin 185-9
182915 Rapid Grower Broth Suscep. 998560 Clarithromycin 189-1
182915 Rapid Grower Broth Suscep. 998211 Doxycycline 225-3
182915 Rapid Grower Broth Suscep. 998561 Imipenem 279-0
182915 Rapid Grower Broth Suscep. 998562 Linezolid 29254-0
182915 Rapid Grower Broth Suscep. 998212 Minocycline 335-0
182915 Rapid Grower Broth Suscep. 998210 Moxifloxacin 31037-5
182915 Rapid Grower Broth Suscep. 998213 Tigecycline 42355-8
182915 Rapid Grower Broth Suscep. 998564 Tobramycin 508-2
Reflex Table for Organism ID
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 000000 Antimicrobial Susceptibility 000000 Antimicrobial Susceptibility N/A

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