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Journal of Bacteriology, September 2009, p. 5419-5427, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00369-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Selection, Recombination, and Virulence Gene Diversity among Group B Streptococcal Genotypes{triangledown} ,{dagger}

A. Cody Springman,1,2 David W. Lacher,1,{ddagger} Guangxi Wu,1,2 Nicole Milton,1,2 Thomas S. Whittam,1 H. Dele Davies,2 and Shannon D. Manning1,2*

Microbial Evolution Laboratory, National Food Safety and Toxicology Center,1 Department of Pediatrics and Human Development, Michigan State University, East Lansing, Michigan 488242

Received 17 March 2009/ Accepted 23 June 2009

Transmission of group B Streptococcus (GBS) from mothers to neonates during childbirth is a leading cause of neonatal sepsis and meningitis. Although subtyping tools have identified specific GBS phylogenetic lineages that are important in neonatal disease, little is known about the genetic diversity of these lineages or the roles that recombination and selection play in the generation of emergent genotypes. Here, we examined genetic variation, selection, and recombination in seven multilocus sequence typing (MLST) loci from 94 invasive, colonizing, and bovine strains representing 38 GBS sequence types and performed DNA sequencing and PCR-based restriction fragment length polymorphism analysis of several putative virulence genes to identify gene content differences between genotypes. Despite the low level of diversity in the MLST loci, a neighbor net analysis revealed a variable range of genetic exchange among the seven clonal complexes (CCs) identified, suggesting that recombination is partly responsible for the diversity observed between genotypes. Recombination is also important for several virulence genes, as some gene alleles had evidence for lateral gene exchange across divergent genotypes. The CC-17 lineage, which is associated with neonatal disease, is relatively homogeneous and therefore appears to have diverged independently with an exclusive set of virulence characteristics. These data suggest that different GBS genetic backgrounds have distinct virulence gene profiles that may be important for disease pathogenesis. Such profiles could be used as markers for the rapid detection of strains with an increased propensity to cause neonatal disease and may be considered useful vaccine targets.

* Corresponding author. Mailing address: National Food Safety and Toxicology Center, Michigan State University, East Lansing, MI 48824. Phone: (517) 884-2066. Fax: (517) 432-2310. E-mail: Shannon.Manning{at}ht.msu.edu

{triangledown} Published ahead of print on 6 July 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: U.S. Food and Drug Administration, Division of Molecular Biology, Center for Food Safety and Applied Nutrition, 8301 Muirkirk Road, Laurel, MD 20708.

Journal of Bacteriology, September 2009, p. 5419-5427, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00369-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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