Sequence type 1 group B Streptococcus, an emerging cause of invasive disease in adults, evolves by small genetic changes. Academic Article uri icon


  • The molecular mechanisms underlying pathogen emergence in humans is a critical but poorly understood area of microbiologic investigation. Serotype V group B Streptococcus (GBS) was first isolated from humans in 1975, and rates of invasive serotype V GBS disease significantly increased starting in the early 1990s. We found that 210 of 229 serotype V GBS strains (92%) isolated from the bloodstream of nonpregnant adults in the United States and Canada between 1992 and 2013 were multilocus sequence type (ST) 1. Elucidation of the complete genome of a 1992 ST-1 strain revealed that this strain had the highest homology with a GBS strain causing cow mastitis and that the 1992 ST-1 strain differed from serotype V strains isolated in the late 1970s by acquisition of cell surface proteins and antimicrobial resistance determinants. Whole-genome comparison of 202 invasive ST-1 strains detected significant recombination in only eight strains. The remaining 194 strains differed by an average of 97 SNPs. Phylogenetic analysis revealed a temporally dependent mode of genetic diversification consistent with the emergence in the 1990s of ST-1 GBS as major agents of human disease. Thirty-one loci were identified as being under positive selective pressure, and mutations at loci encoding polysaccharide capsule production proteins, regulators of pilus expression, and two-component gene regulatory systems were shown to affect the bacterial phenotype. These data reveal that phenotypic diversity among ST-1 GBS is mainly driven by small genetic changes rather than extensive recombination, thereby extending knowledge into how pathogens adapt to humans.

published proceedings

  • Proc Natl Acad Sci U S A

altmetric score

  • 7.6

author list (cited authors)

  • Flores, A. R., Galloway-Pea, J., Sahasrabhojane, P., Saldaa, M., Yao, H., Su, X., ... Shelburne, S. A.

citation count

  • 71

complete list of authors

  • Flores, Anthony R||Galloway-Peña, Jessica||Sahasrabhojane, Pranoti||Saldaña, Miguel||Yao, Hui||Su, Xiaoping||Ajami, Nadim J||Holder, Michael E||Petrosino, Joseph F||Thompson, Erika||Margarit Y Ros, Immaculada||Rosini, Roberto||Grandi, Guido||Horstmann, Nicola||Teatero, Sarah||McGeer, Allison||Fittipaldi, Nahuel||Rappuoli, Rino||Baker, Carol J||Shelburne, Samuel A

publication date

  • May 2015