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Influence of capsular neuraminic acid on properties of streptococci of serological group B.

Neuraminic acid is thought to be a critical virulence factor of group B streptococci. The present study was designed to further characterize a previously described type III group B streptococcus and its transposon-mutagenized asialo capsular mutant. The wild-type group B streptococcus grew as short chains with a uniform turbidity and had diffuse colonies in soft agar media. In contrast, the asialo mutant grew in fluid media as a granular sediment, formed significantly longer chains and had compact colonies in soft agar. These differences, possibly related to the surface charge of the bacteria, could also be demonstrated in salt aggregation tests and hexadecane adherence studies. The wild-type group B streptococcus showed hydrophilic, and the asialo mutant hydrophobic surface properties. Removal of neuraminic acid from the wild-type strain changed the surface properties from hydrophilic to hydrophobic. A similar masking effect of capsular neuraminic acid could be observed in adherence and phagocytosis experiments. In contrast to the wild-type strain, the asialo mutant adhered significantly more to buccal epithelial cells and was phagocytosed more by polymorphonuclear leucocytes. These altered properties might possibly be of importance for group B streptococcal pathogenicity.