Teichoic acids are found within the cell wall of most Gram-positive bacteria such as species in the genera Staphylococcus, Streptococcus, Bacillus, Clostridium, Corynebacterium, and Listeria, and appear to extend to the surface of the peptidoglycan layer. Teichoic acids are not found in Gram-negative bacteria. They can be covalently linked to N-acetylmuramic acid or a terminal D-alanine in the tetrapeptide crosslinkage between N-acetylmuramic acid units of the peptidoglycan layer, or they can be anchored in the cytoplasmic membrane with a lipid anchor. Teichoic acids that are anchored to the lipid membrane are referred to as lipoteichoic acids, whereas teichoic acids that are covalently bound to peptidoglycan are referred to as wall teichoic acids.