Notes: D-Ala-D-Ala is the terminal dipeptide moiety of peptidoglycan in bacterial cell walls and a target of certain antibacterial agents.{68642} Replacement of D-Ala-D-Ala with D-Ala-D-lactate by the combined activity of the enterococcal gene products VanA, VanH, and VanX reduces the affinity of the antibiotic vancomycin (Item No. 15327) for the peptidoglycan and is responsible for vancomycin resistance.