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Sputum (3-5 separate samples);
Acid fast staining (eg, Ziehl-Neelsen) or auramine staining for microscopy;
Rapid growers (eg, M. fortuitum) may grow in 1-2 weeks, but 6-8 weeks of incubation are required before discarding negative cultures.
The use of culture systems using liquid media combined with gene probe (for identification) considerably reduces the time required for testing.
Suspected tuberculosis or atypical mycobacterial infection, including unexplained lung infection;
Biopsy of tissue has higher sensitivity than fluid samples.
The presence of acid fast bacilli in sputum or in normally sterile fluids or tissues is generally sufficient to establish the diagnosis of tuberculosis in the context of a typical clinical presentation.
However, the sensitivity of microscopy in body fluids and CSF is low (<20%).
Use of gene probing after PCR amplification allows more rapid detection and differentiation of Mycobacterium tuberculosis from other mycobacteria; culture confirms the diagnosis and allows identification of non-tuberculous mycobacteria and antibiotic susceptibility testing.
M. leprae cannot be grown in vitro and the diagnosis of leprosy is based on the presence of acid fast bacilli in a clinically suspicious lesion.
Pfyffer GE et al. In: Murray PR et al eds. Manual of Clinical Microbiology. 8th ed. ASM Press 2003.
Hale YM et al. Clin Infect Dis 2001; 33: 834-846.