F2F Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Characterization of the virulence of a highly necrotizing strain of Streptococcus pyogenes (#121)

Geoffrey Deneubourg 1 , Lionel Schiavolin 1 , Valérie Delforge 1 , Dalila Lakhloufi 1 , Mark Davies 2 , Pierre R. Smeesters 1 3 4 5 , Anne Botteaux 1
  1. Molecular Bacteriology Laboratory, Université Libre de Bruxelles, Brussels, Belgium
  2. Doherty Institute, University of Melbourne, Melbourne, VIC, Australia
  3. Paediatric Department, Academic Children Hospital Queen Fabiola, Université Libre de Bruxelles, Brussels, Belgium
  4. Tropical Diseases Research Group, Murdoch Children's Research Institute, Melbourne, VIC, Australia
  5. Department of Paediatrics, University of Melbourne, Melbourne, VIC, Australia

Background: Group A Streptococcus (GAS) causes more than 500.000 deaths per year. GAS is responsible for a broad spectrum of diseases ranging from pharyngitis to life-threatening invasive diseases. GAS virulence is due to a complex interplay between host factors and bacterial factors, including DNases. The L01, a clinical GAS isolate, was retrieved from a nosocomial case of necrotizing fasciitis. As the L01 has 4 DNases, we hypothesize that these virulence factors could contribute to its phenotype.

Methods: To investigate the contribution of DNases, or/and other virulence factors, to pathogenesis of invasive GAS disease, we studied the L01 and a DNase KO mutant constructed in the lab in different virulence tests such as growth curves, whole blood survival, biofilm formation, etc…. We have also studied the potential contribution of other virulence factors by studying L01 transcriptome via RNASeq under relevant conditions.

Results: No difference was observed between the L01 and the mutant in biofilm formation, adhesion/invasion, whole blood survival and most of growth curves. Surprisingly, the KO mutant has a better growth in human serum than the L01. The RNASeq in different conditions showed us that 5 genes could potentially explain the extreme phenotype of the strain.

Conclusions: The studied DNase don’t seem to play a role in a major part of the virulence of the L01 even if the phenotype in human serum is interesting. More RNASeq studies are currently ongoing to try to explain this phenotype.