Sialic acids are a structurally complex family of nine-carbon monosaccharides and they typically occupy the terminal positions of many eukaryotic surface-exposed glycoconjugates that function in diverse cellular processes such as intercellular adhesion and cell signaling.Some pathogenic bacteria use sialic acids to masquerade their cell surfaces and protect themselves from host immune attacks.These pathogenic bacteria obtain sialic acids either through de novo biosynthesis or donor scavenging that is often mediated via sialidase, an enzyme that cleaves terminal sialic acids from different glycoconjugates.