1. The Acid Fast Cell Wall
Dr. Jennifer Coetzee

2. Definition
Cell wall that retains carbol fuchsin dye in the presence of acid alcohol
Stains use in lab to detect acid fastness:
Ziehl-Neelsen
Kinyoun

4. Organisms with Acid Fast Cell Wall
Mycobacteria
Mycobacterium tuberculosis
Mycobacterium leprae
Mycobacterium bovis
57 other mycobacterial species!
Nocardia species
Nocardia asteroides
And many more

5. Structure of an Acid Fast Cell Wall
3 major molecules:
Peptidoglycans
Contains N-glycolylmuramic acid instead of N-acetylmuramic acid found in other bacteria
Prevents osmotic lysis
Arabinogalactans
2 lipopolysaccharides, lipoarabinomannan (LAM) and lipomannan
Mycolic acids

7. Mycolic Acids Almost exclusive to mycobacteria
Essential to acid fast staining properties
Up to 60% of composition of mycobacterial cell wall
Branched fatty acids with a short and long branch (22-24 and carbons)
MTB genome 4000 genes
Mostly coding for enzymes involved in lipolysis and lipogenesis

8. Lipoarabinomannan Directs macrophage function
Inhibits the processing of mycobacterial peptides/proteins by antigen presenting cells
Induces tumor necrosis factor (TNF-ά)
Considered a mycobacterial virulence factor

9. Permeability of Cell Wall
Membrane proteins called porins control diffusion of hydropilic molecules
Relatively impermeable to hydrophilic solutes
Permeability of lipophilic molecules:
Inner leaflet low fluidity, nearly crystalline structure
Diffusion through lipid bilayer requires fluid interior
Bilayer uncommonly thick

10. Clinical Implications
High degree of intrinsic resistance to most antibiotics
Low permeability
Unusual structure
Slow growth rate
Clinicians awaiting culture results!

11. Target for design of new drugs Vaccine development
Relatively resistant to drying, alkali, and many more chemical disinfectants
Very difficult to prevent transmission of M. tuberculosis in institutions
Infection control implications
Target for design of new drugs
Vaccine development
Better understanding of pathogenesis, immunity

12. Summary Cell wall structure totally different from other bacteria
Mycolic acids major component, responsible for acid fast staining characteristic
Also peptidoglycan, arabinogalactans
Clinical implications of the above

13. References
Rodrigo Gay Ducati et al. The resumption of consumption. Mem Inst Oswaldo Cruz, 101(7), 2006
Brennan PJ, Nikaido H. The envelope of mycobacteria. Annu Rev Biochem. 1995;64:29-63
Barry CE, Mdluli K. Drug sensitivity and environmental adaptation of mycobacterial cell wall components. Trends Microbiol. 1996;4(7):275-81