Bacterial peptidoglycan is a giant macromolecule formed from linear glycan chains, interlinked by short peptides. The glycan chains are made up from alternating units of N-acetyl-glucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc), with all linkage between sugars being Beta:1-4. The carboxyl group of each N-acetyl-muramic acid residue is substituted by a peptide subunit. In newly formed peptidoglycan, this subunit is usually of the form: L-Ala-y-D-Glu-meso-Dap-D-Ala-D-Ala (i.e. a pentapeptide), whiereas in mature peptidoglycan one, or both, of the D-alanine residues is lost (van Heijenoort, 2001).

The neighbouring glycan chains are interlinked either by a direct peptide linkage between the peptide subunits of two chains, or by a short peptide bridge between two peptide subunits (van Heijenoot, 2001).