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Characterization of an isogenic mutant of Streptococcus pyogenes Manfredo lacking the ability to make streptococcal

B A Degnan1, M C Fontaine, A H Doebereiner

  • 1School of Clinical Medical Sciences (Rheumatology), Medical School, University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom. pm274@cam.ac.uk

Infection and Immunity
|April 18, 2000
PubMed

Insights

Streptococcus pyogenes lacking streptococcal acid glycoprotein (SAGP) showed reduced invasion and impaired survival under acidic conditions. This suggests SAGP, and its arginine deiminase (AD) activity, are crucial for bacterial virulence and acid resistance.

Area of Science:

  • Microbiology
  • Immunology
  • Molecular Biology

Background:

  • Streptococcus pyogenes is an important human pathogen.
  • Streptococcal acid glycoprotein (SAGP) is a surface protein of S. pyogenes.
  • The function of SAGP and its associated enzyme, arginine deiminase (AD), in S. pyogenes pathogenesis is not fully understood.

Purpose of the Study:

  • To investigate the role of SAGP and AD activity in S. pyogenes invasion, immune cell modulation, and acid survival.
  • To confirm that SAGP possesses AD activity.

Main Methods:

  • Construction of an isogenic mutant of S. pyogenes Manfredo lacking SAGP using allelic exchange.
  • Enzyme assays of cell extracts for arginine deiminase (AD) activity.
  • Inhibition assays of human peripheral blood mononuclear cell proliferation.
  • Epithelial cell invasion assays.
  • Assessment of bacterial viability under acidic conditions with and without L-arginine.

Main Results:

  • The sagp mutant lacked detectable AD activity, confirming SAGP possesses AD activity.
  • Wild-type cell extracts inhibited mitogen-stimulated peripheral blood mononuclear cell proliferation, an effect reversed by L-arginine.
  • The sagp mutant exhibited a 3-5 fold reduction in epithelial cell invasion compared to wild-type.
  • L-arginine significantly increased wild-type S. pyogenes viability at low pH, but not the mutant's.

Conclusions:

  • SAGP, possessing arginine deiminase (AD) activity, is essential for S. pyogenes invasion of epithelial cells.
  • AD activity contributes to S. pyogenes's ability to survive acidic environments, potentially through L-arginine metabolism.
  • These findings highlight SAGP and AD as potential targets for therapeutic intervention against S. pyogenes infections.

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