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Nonhemolytic Group B Streptococcus (GBS) strains can be hypervirulent, contrary to previous assumptions. A specific genetic mutation in CovS reduces hemolysis but enhances GBS hyaluronidase activity, increasing virulence in neonates.

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Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Neonatal Infections

Background:

  • Group B Streptococcus (GBS) is a primary cause of serious neonatal infections.
  • Hemolytic activity is generally considered crucial for GBS virulence.
  • Nonhemolytic GBS strains are typically presumed to be less virulent.

Purpose of the Study:

  • To investigate the virulence of a nonhemolytic GBS strain isolated from a septic neonate.
  • To elucidate the molecular mechanisms underlying hypervirulence in nonhemolytic GBS.

Main Methods:

  • Isolation and characterization of a hypervirulent nonhemolytic GBS strain (GB37).
  • Genetic analysis of the sensor histidine kinase CovS.
  • Assessing the impact of CovS mutations on hemolytic activity and hyaluronidase (HylB) function.

Main Results:

  • A nonhemolytic GBS strain (GB37) demonstrated hypervirulence in a neonatal sepsis model.
  • A specific mutation (W297L) in CovS led to constitutive kinase signaling.
  • This mutation resulted in decreased bacterial hemolysis and significantly increased hyaluronidase (HylB) activity.

Conclusions:

  • Nonhemolytic GBS strains can possess hypervirulent potential.
  • CovS signaling pathway modulation influences GBS virulence factors, including hemolysis and hyaluronidase.
  • Understanding these mechanisms is critical for diagnosing and treating neonatal GBS infections.