Gram-positive organisms	Gram-negative organisms	Mycobacteria
The lipid bilayer cell membrane of most of the Gram-positive bacteria is covered by a porous peptidoglycan layer which does not exclude most antimicrobial agents.	Gram-negative bacteria are surrounded by two membranes. The outer membrane functions as an efficient permeability barrier because it contains lipopolysaccharides (LPS) and porins.	Mycobacteria produce a thick mycolate-rich outer covering which functions as an exceptionally efficient barrier.
lipid bilayer peptidoglycan lipid + LPS porins MYCOLATE acyl lipids LAM arabinogalactan

Graphics © Copyright Linda M Stannard, 1996.