The Ziehl-Neelsen (ZN) stain was developed to exploit the mycobacterial genus' acid fastness (for a review of basic mycobacteriology laboratory practice, see [15,16]). For more than a century, conventional light microscopy using ZN-stained smears prepared directly from sputum specimens has been the most widely available test for diagnosis of TB in resource-limited settings. ZN AFB staining is inexpensive and results are rapidly available, and therefore has been a cornerstone of the World Health Organization and STOP TB control strategy.However, any sputum AFB staining is limited in sensitivity (especially for HIV-infected patients and children), useless for extrapulmonary TB and species identification (i.e. cannot reliably distinguish among species of the genus or the M. tuberculosis complex), and is dependent on acquiring sputum, which may be impossible for some patients, especially young children.