Sialidases have been suggested to be pathogenic factors in microbial infections. Hydrolysis of alpha-(2->3)-, alpha-(2->6)-, alpha-(2->8)- glycosidic linkages of terminal sialic acid residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates. Belongs to the glycosyl hydrolase 33 family.