A group B streptococcal pilus protein promotes phagocyte resistance and systemic virulence

FASEB J. 2008 Jun;22(6):1715-24. doi: 10.1096/fj.07-093963. Epub 2008 Jan 15.


Group B Streptococcus (GBS) is a major cause of invasive bacterial infections in newborns and certain adult populations. Surface filamentous appendages known as pili have been recently identified in GBS. However, little is known about the role of these structures in disease pathogenesis. In this study we sought to probe potential functional role(s) of PilB, the major GBS pilus protein subunit, by coupling analysis of an isogenic GBS pilB knockout strain with heterologous expression of the pilB gene in the nonpathogenic bacterium Lactococcus lactis. We found the knockout GBS strain that lacked PilB was more susceptible than wild-type (WT) GBS to killing by isolated macrophages and neutrophils. Survival was linked to the ability of PilB to mediate GBS resistance to cathelicidin antimicrobial peptides. Furthermore, the PilB-deficient GBS mutant was more readily cleared from the mouse bloodstream and less-virulent in vivo compared to the WT parent strain. Strikingly, overexpression of the pilB gene alone in L. lactis enhanced resistance to phagocyte killing, increased bloodstream survival, and conferred virulence in a mouse challenge model. Together these data demonstrate that the pilus backbone subunit, PilB, plays an integral role in GBS virulence and suggests a novel role for gram-positive pili in thwarting the innate defenses of phagocyte killing.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antimicrobial Cationic Peptides / pharmacology
  • Bacterial Proteins / physiology*
  • Drug Resistance, Bacterial
  • Fimbriae Proteins / physiology*
  • Fimbriae, Bacterial
  • Humans
  • Lactococcus lactis
  • Macrophages, Peritoneal
  • Mice
  • Neutrophils
  • Oxidoreductases / physiology*
  • Phagocytes / immunology*
  • Streptococcus / chemistry
  • Streptococcus / pathogenicity*
  • Streptococcus / ultrastructure
  • Virulence


  • Antimicrobial Cationic Peptides
  • Bacterial Proteins
  • Fimbriae Proteins
  • ropocamptide
  • Oxidoreductases
  • pilB protein, Bacteria