Atypical mycobacteria: an important differential for the general physician.

Atypical mycobacteria, or more correctly nontuberculous mycobacterial (NTM) species, are a ubiquitous group of environmental organisms that have potential to cause pathological presentations, varying from skin and superficial infections to deeper infections with or without systemic dissemination. Many NTM species are well-recognised pathogens, whereas others are newly emerging and their pathogenic potential is yet to be understood. Some features of NTM pathologies are shared with diseases caused by the biologically related M. tuberculosis, but there are significant differences. The microbiological classification of NTM depends on two main factors:1 rate of growth (rapid growing or slow growing) and pigment production. Table 1 lists some of the clinically important NTM organisms.2,3