Four isolates of a rapidly growing Mycobacterium species had a mycolic acid pattern similar to that of Mycobacterium smegmatis, as determined by HPLC analyses. Three of the isolates were from footbath drains and a sink at a nail salon located in Atlanta, GA, USA; the fourth was obtained from a granulomatous subdermal lesion of a female patient in Venezuela who was undergoing mesotherapy. By random amplified polymorphic DNA electrophoresis and PFGE of large restriction fragments, the three isolates from the nail salon were shown to be the same strain but different from the strain from the patient in Venezuela. Polymorphisms in regions of the rpoB, hsp65 and 16S rRNA genes that were shown to be useful for species identification matched for the two strains but were different from those of other Mycobacterium species. The 16S rRNA gene sequence placed the strains in a taxonomic group along with Mycobacterium frederiksbergense, Mycobacterium hodleri, Mycobacterium diernhoferi and Mycobacterium neoaurum. The strains produced a pale-yellow pigment when grown in the dark at the optimal temperature of 35 degrees C. Biochemical testing showed that the strains were positive for iron uptake, nitrate reduction and utilization of d-mannitol, d-xylose, iso-myo-inositol, l-arabinose, citrate and d-trehalose. The strains were negative for d-sorbitol utilization and production of niacin and 3-day arylsulfatase, although arylsulfatase activity was observed after 14 days. The isolates grew on MacConkey agar without crystal violet but not on media containing 5 % (w/v) NaCl or at 45 degrees C. They were susceptible to ciprofloxacin, amikacin, tobramycin, cefoxitin, clarithromycin, doxycycline, sulfamethoxazole and imipenem. The name Mycobacterium cosmeticum sp. nov. is proposed for this novel species; two strains, LTA-388(T) (=ATCC BAA-878(T)=CIP 108170(T)) (the type strain) and 2003-11-06 (=ATCC BAA-879=CIP 108169) have been designated, respectively, for the strains of the patient in Venezuela and from the nail salon in Atlanta, GA, USA.