 "Mycobacterium abscessus" and "M. chelonae" can be distinguished from "M. fortuitum" or "M. peregrinum" by their failure to reduce nitrate and to take up iron.Tolerance to 5% NaCl in Löwenstein-Jensen media, tolerance to 0.2% picrate in Sauton agar, and non-utilisation of citrate as a sole carbon source are characteristics that distinguish "M. abscessus" from "M.