Detection and Localisation of Sialic Acid inGardnerella vaginalis, Mobiluncusspp., and Other Vaginal Microorganisms

Abstract

Sialic acid, n-acetylneuraminic acid, is found in the cell wall of all serotypes of group B Streptococcus and Escherichia coli serotypes K1 and K3. It has been most strongly associated with those strains which cause neonatal meningitis. The purpose of this study is to report the presence of sialic acid in some genital tract bacteria. Bacteria were grown to log phase. Mild-acid hydrolysis of whole organisms released a compound which reacted positively in the periodatethiobarbituric acid (PTA) assay, a colorimetric assay detecting n-acetylneuraminic acid. Surface localisation of sialic acid was supported by the observation of bacterial agglutination with an affinity-purified lectin ( Limulus polyphemus agglutinin) which binds sialic acid residues. Four vaginal isolates of Mobiluncus curtisii and three vaginal isolates of Mobiluncus mulieris strains tested contained a level of sialic acid equivalent to that of the group B Streptococcus control by PTA assay. Four Gardnerella vaginalis strains (three vaginal and two placental isolates) were positive for sialic acid by PTA assay. Nine clinical vaginal isolates of Peptostreptococcus : P. anaerobius (2), P. asaccharolyticus (3), P. magnus (2) and P. tetradius (2) were negative for sialic acid. Two clinical vaginal isolates of Enterococcus faecalis and four diphtheroid isolates were also negative. Eleven clinical vaginal isolates of viridans streptococci including S. intermedius (5) , S. constellatus (4), and S. acidominimus (2) were negative for sialic acid. One of three clinical vaginal isolates of S. acidominimus , one of four clinical vaginal isolates of coagulase negative staphylococci and two of seven clinical vaginal isolates of lactobacilli tested positive for low levels of sialic acid. All strains in which sialic acid was detected by PTA assay showed surface localisation by lectin agglutination. The presence of sialic acid on the surface of Gardnerella and Mobiluncus , two organisms associated with bacterial vaginosis, may be associated with their capacity to colonise or infect the genital tract. Keywords: Sialic acid; Mobiluncus spp.; Gardnerella vaginalis ; vaginal bacteria.