Responsible for O-acetylation at the C(6)-hydroxyl group of N-acetylmuramyl residues, forming the corresponding N,6-O-diacetylmuramic acid of the peptidoglycan (PubMed:15661003, PubMed:32350117). O-acetylation of the peptidoglycan is the major determinant for lysozyme resistance (PubMed:15661003). Monomer. Belongs to the acyltransferase 3 family.