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Within-host competition drives selection for the capsule virulence determinant of Streptococcus pneumoniae

Elena S Lysenko1, Rebeccah S Lijek, Sam P Brown

  • 1Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.

Current Biology : CB
|July 13, 2010
PubMed

Insights

Microbial competition can drive the evolution of virulence. In nasal colonization, Haemophilus influenzae

Area of Science:

  • Microbiology
  • Evolutionary Biology
  • Pathogenesis

Background:

  • Opportunistic pathogens' virulence evolution is not fully understood, especially when host damage offers no clear advantage.
  • Pathogens interact with hosts on mucosal surfaces, competing with resident microflora for niches.

Purpose of the Study:

  • To investigate if interspecies microbial competition promotes the acquisition of virulence characteristics.
  • To understand the role of microbial competition in the evolution of pathogenic traits.

Main Methods:

  • A model murine nasal colonization system was used to study interactions between Haemophilus influenzae and Streptococcus pneumoniae.
  • Neutrophil recruitment and complement-mediated killing of S. pneumoniae by H. influenzae were analyzed.
  • Interspecies interaction modeling and experimental colonization studies were conducted.

Main Results:

  • Haemophilus influenzae outcompeted Streptococcus pneumoniae by inducing neutrophil-mediated killing of S. pneumoniae.
  • Streptococcus pneumoniae's polysaccharide capsule conferred resistance to opsonophagocytic clearance, enhancing survival during competition.
  • More virulent S. pneumoniae strains, expressing capsules conferring resistance, showed increased survival against H. influenzae.

Conclusions:

  • Competition between commensal microbes can select for virulence factors, even if costly to produce.
  • These selected virulence characteristics may predispose microbes to causing invasive disease.
  • Microbial competition during commensalism is a potential evolutionary driver for pathogen virulence.

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