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Rapidly-growing Mycobacterium Susceptibility−Broth Dilution
- M abscessus Susceptibility Testing
- M chelonae Susceptibility Testing
- M fortuitum Complex Susceptibility Testing
- AFB Susceptibility Testing
- Rapid-grower Susceptibility Testing
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)
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.
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
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
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|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|
|182915||Rapid Grower Broth Suscep.||998563||Trimethoprim/Sulfa||516-5|
|182915||Rapid Grower Broth Suscep.||182862||Please note:||N/A|
|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|