Identification and characterization of NanH2 and NanH3, enzymes responsible for sialidase activity in the vaginal bacterium .

is abundant in bacterial vaginosis (BV), a condition associated with adverse reproductive health. Sialidase activity is a diagnostic feature of BV and is produced by a subset of strains. Although its genetic basis has not been formally identified, sialidase activity is presumed to derive from the gene, named here In this study, BLAST searches predicted two additional sialidases, NanH2 and NanH3. When expressed in , NanH2 and NanH3 both displayed broad abilities to cleave sialic acids from α2-3- and α2-6-linked - and -linked sialoglycans, including relevant mucosal substrates. In contrast, recombinant NanH1 had limited activity against synthetic and mucosal substrates under the conditions tested. Recombinant NanH2 was much more effective than NanH3 in cleaving sialic acids bearing a 9--acetyl ester. Similarly, strains encoding NanH2 cleaved and foraged significantly more Neu5,9Ac than strains encoding only NanH3. Among a collection of 34 isolates, , , or both were present in all 15 sialidase-positive strains but absent from all 19 sialidase-negative isolates, including 16 strains that were -positive. We conclude that NanH2 and NanH3 are the primary sources of sialidase activity in and that these two enzymes can account for the previously described substrate breadth cleaved by sialidases in human vaginal specimens of women with BV. Finally, PCRs of or from human vaginal specimens had 81% sensitivity and 78% specificity in distinguishing between dominance and BV, as determined by Nugent scoring.