Gram postive and negative bacteria have key structural differences, which are important when considering treatment of diseases caused by these bacteria due to wider treatment implications.
Bacterial cell walls in gram positive and negative bacteria have many differences. Both gram-positive and gram-negative bacteria have a cell wall made up of peptidoglycan, a linear polypeptide consisting of alternating units of N-acetylmumeric acid and N-actylglucosamine.
Gram positive bacteria:
- Thick peptidoglycan layer (20-40nm thick)Cite error: Invalid
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- High level of cross bridging between adjacent peptides.
- Contains anionic polymers - teichoic acid and lipoteichoic acid. Teichoic acids are polymers of glycerol or ribotol linked by phosphodiester bonds and are covalently attached to N-acetylmumaric acid residues in peptidoglycan.. Lipoteichoic acids are polymers of glycerol phosphate and are substituted with D-alanine and sugars. They are covalently attached to membrane lipids. Teichoic and lipoteichoic acids extend to the surface of peptidoglycan layer and may contribute to the overall net negative charge of gram positive bacteria. Both are antigenic and are major somatic antigens of gram positive bacteria.
Gram negative bacteria:
- More complex, multilayered structure
- Peptidoglycan is a much thinner layer and is highly hydrated, forming the periplasm between the outer membrane and cytoplasm Cite error: Invalid
name cannot be a simple integer. Use a descriptive title. There is a low degree of cross linkage which results in the formation of periplasmic gel, through which proteins can freely diffuse. Compression of the gel by sudden reduction in external osmotic pressure (osmotic shock) results in release of enzymes and other proteins within the periplasm.
- The inner leaflet of the outer membrane consists mainly of phospholipids.
- The outer leaflet is composed of lipopolysaccharide (LPS). LPS is an amphipathic molecule with 3 regions; glycolipid, a core oligosaccharide containing sugar acid KDO and an O antigen, which varies between species. LPS is a major somatic antigen of gram negative bacteria. O antigen side chains can be rapidly changed to avoid immune detection.