FIG. 2.

Diagram of peptidoglycan structures from S. aureus, S. pyogenes, and L. monocytogenes. Glycan chains composed of a repeating disaccharide, GlcNAc and MurNAc, are linked to short wall peptides through the lactyl moeity of MurNAc. Adjacent wall peptides can be linked through crossbridge peptides (pentaglycine in S. aureus or dialanine in S. pyogenes). In some cases, such as L. monocytogenes, adjacent wall peptides are not cross-linked via peptide crossbridges. Instead, wall peptides are linked via an amide bond between the ɛ-amino group of a meso-diaminopimelic acid (m-Dpm) residue at position 3 of one wall peptide and the carboxy terminus of the d-alanyl residue at position 4 of the adjacent wall peptide.