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Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells
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Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells

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Streptococcal pyrogenic exotoxin B causes mitochondria damage to polymorphonuclear cells preventing phagocytosis of

Chuan Chiang-Ni1, Chih-Hung Wang, Pei-Jane Tsai

  • 1Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan.

Medical Microbiology and Immunology
|August 2, 2005
PubMed

Insights

Group A Streptococcus pyrogenic exotoxin B (SpeB) aids bacterial survival by damaging immune cells. SpeB disrupts polymorphonuclear (PMN) cell mitochondria, hindering early infection clearance.

Area of Science:

  • Microbiology
  • Immunology
  • Molecular Biology

Background:

  • Streptococcal pyrogenic exotoxin B (SpeB) is implicated in Group A Streptococcus (GAS) survival in the bloodstream.
  • The precise mechanism by which SpeB contributes to GAS survival remains unclear.

Purpose of the Study:

  • To elucidate the role of SpeB in GAS resistance to phagocytosis.
  • To investigate the effect of SpeB on polymorphonuclear (PMN) cell function.

Main Methods:

  • Construction and confirmation of speB isogenic mutants of GAS strains M6 and M49.
  • Phagocytosis assays using wild-type and speB mutant strains in whole blood and plasma.
  • Incubation of speB mutants with recombinant SpeB (r-SpeB) and a catalytically inactive mutant (r-C192S).
  • Analysis of PMN cell viability, mitochondrial dehydrogenase activity, and membrane potential.

Main Results:

  • speB mutants exhibited a five-fold increase in phagocytosis compared to wild-type strains in whole blood.
  • Recombinant SpeB (r-SpeB) restored resistance to phagocytosis in speB mutants, while the inactive mutant (r-C192S) did not.
  • r-SpeB treatment led to decreased mitochondrial dehydrogenase activity and loss of membrane potential in PMN cells.

Conclusions:

  • SpeB enhances GAS survival by directly damaging PMN cell mitochondria.
  • This mitochondrial damage impairs phagocytic clearance, facilitating early-stage infection by GAS.

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