Nearly two dozen microbial pathogens have surface polysaccharides or lipo-
oligosaccharides that contain sialic acid (Sia), and several Sia-dependent virulence
mechanisms are known to enhance bacterial survival or result in host tissue injury. Some
pathogens are also known to O-acetylate their Sias, although the role of this modification in
pathogenesis remains unclear. We report that neuD, a gene located within the Group B
Streptococcus (GBS) Sia biosynthetic gene cluster, encodes a Sia O-acetyltransferase that is …