Open Access Research article

The frequency of genes encoding three putative group B streptococcal virulence factors among invasive and colonizing isolates

Shannon D Manning1, Moran Ki2, Carl F Marrs3, Kiersten J Kugeler4, Stephanie M Borchardt5, Carol J Baker6 and Betsy Foxman3*

Author Affiliations

1 National Food Safety and Toxicology Center and Department of Pediatrics and Human Development, Michigan State University, East Lansing, Michigan, USA

2 Department of Preventive Medicine, Eulji University School of Medicine, Daejeon, Korea

3 Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan, USA

4 Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, Bacterial Zoonoses Branch, Fort Collins, Colorado, USA

5 Fargo Veterans Administration Medical Center, Fargo, North Dakota, USA

6 Department of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA

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BMC Infectious Diseases 2006, 6:116  doi:10.1186/1471-2334-6-116

Published: 17 July 2006



Group B Streptococcus (GBS) causes severe infections in very young infants and invasive disease in pregnant women and adults with underlying medical conditions. GBS pathogenicity varies between and within serotypes, with considerable variation in genetic content between strains. Three proteins, Rib encoded by rib, and alpha and beta C proteins encoded by bca and bac, respectively, have been suggested as potential vaccine candidates for GBS. It is not known, however, whether these genes occur more frequently in invasive versus colonizing GBS strains.


We screened 162 invasive and 338 colonizing GBS strains from different collections using dot blot hybridization to assess the frequency of bca, bac and rib. All strains were defined by serotyping for capsular type, and frequency differences were tested using the Chi square test.


Genes encoding the beta C protein (bac) and Rib (rib) occurred at similar frequencies among invasive and colonizing isolates, bac (20% vs. 23%), and rib (28% vs. 20%), while the alpha (bca) C protein was more frequently found in colonizing strains (46%) vs, invasive (29%). Invasive strains were associated with specific serotype/gene combinations.


Novel virulence factors must be identified to better understand GBS disease.