An order of gram-negative nonmotile bacteria that do not possess a true cell wall but are instead enclosed by a three-layered membrane and include pathogenic and saprophytic species, such as Mycoplasma pneumoniae.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.