Definition of a Bacterial Virulence Factor: Sialylation of the Group B Streptococcal Capsule

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 86; no. 22; pp. 8983 - 8987
• Main Authors: Wessels, Michael R., Rubens, Craig E., Benedi, Vicente-Javier, Kasper, Dennis L.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.11.1989; National Acad Sciences
• Subjects: Antibodies; Antigens; Antiserum; Bacterial Toxins - genetics; Bacteriology; Biological and medical sciences; Capsules; DNA Transposable Elements; Electron microscopy; Enzyme-Linked Immunosorbent Assay; Fluorescent Antibody Technique; Fundamental and applied biological sciences. Psychology; Immunoblotting; Immunodiffusion; Microbiology; Microscopy, Electron; Mutation; Nucleic Acid Hybridization; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Plasmids; Polysaccharides; Polysaccharides, Bacterial - genetics; Sialic Acids - analysis; Streptococcus agalactiae; Streptococcus agalactiae - genetics; Streptococcus agalactiae - pathogenicity; Streptococcus agalactiae - ultrastructure; Transposons; Virulence; Virulence factors; Sialic acid; Pathogenesis; Transposon; Gene expression; Electron microscopy; Microorganism capsule; Streptococcaceae; Streptococcus B; Microorganism culture; Immunoblotting assay; Bacteria; Micrococcales; Mutation; Immunofluorescence; ELISA assay
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.86.22.8983

Sialylation of bacterial capsules has been proposed as an important virulence factor for several species of encapsulated pathogens, including group B Streptococcus. We have constructed a transposon mutant strain of type III group B Streptococcus that expresses a capsular polysaccharide differing from the wild type only in that the mutant strain's capsule lacks sialic acid. The mutant polysaccharide is antigenically identical to the capsular polysaccharide of type 14 Streptococcus pneumoniae, as predicted by the structures of the type III group B Streptococcus and S. pneumoniae polysaccharides. Loss of capsular sialic acid was associated with loss of virulence in the mutant strain in a neonatal rat model of lethal group B Streptococcus infection. These studies demonstrate directly that capsular sialic acid is a critical virulence determinant for type III group B Streptococcus and support the general hypothesis that surface sialylation aids pathogenic microorganisms in evading host defenses.