In the [[Runyon classification]], all three are nonchromogens. They can be differentiated from ''M. tuberculosis'' and each other by commercially available [[DNA probes]].<ref name=Tropical>{{cite book|last1=Jones-Lopez|first1=Edward C.|last2=Ellner|first2=Jerrold J.|editor1-last=Guerrant|editor1-first=Richard L.|editor2-last=Walker|editor2-first=David H.|editor3-last=Weller|editor3-first=Peter F.|title=Tropical infectious diseases : principles, pathogens, & practice|date=2011|publisher=Saunders|___location=Edinburgh|isbn=9780702039355|edition=3rd|chapter=Chapter 35: Tuberculosis and Atypical Mycobacterial Infections}}</ref>{{rp|245}}
They are characterized as [[Gram-positive]], nonmotile, [[acid-fast]], short to long rods.
