Diagnosis:
Mycobacterial Tests
• Culture using both solid and liquid media is the gold standard for isolating mycobacteria. Biochemical tests, such as the niacin test, can be used to identify mycobacteria to the species level.
• Nucleic acid amplification tests (NAATs) for identifying the Mycobacterium tuberculosis complex must be performed in conjunction with culture and should be tested on acid-fast, smear-positive respiratory specimens.
• DNA probe assays are commonly used to identify Mycobacterium tuberculosis complex (MTBC), Mycobacterium avium complex (MAC), M. kansasii, and M. gordonae from acid-fast smear-positive cultures.
• Mycobacterium bovis and the vaccine strain, M. bovis BCG, are members of the Mycobacterium tuberculosis complex that should be differentiated from the other species in the complex, especially in initial isolates.
• Once growth is detected on culture media, mycobacteria can be rapidly identified to the species level by DNA probes, DNA sequencing, line probes, or high-pressure liquid chromatography.
• Fluorochrome-stained smears (examined under low-power magnification) are recommended over carbol fuchsin stains, which require oil immersion, when screening for acid-fast bacilli (AFB) in clinical specimens. Increased sensitivity and rapid smear examination are the advantages of fluorescent stains.
Della-Latta P, Jost K, Roberts G, et al: Mycobacterium tuberculosis: assessing your laboratory. Association of Public Health Laboratories, 2009.