Background: Group A Streptococcus (GAS) is a human host pathogen leading to a broad-spectrum of infectious manifestation, for which no vaccine is available. One major barrier to vaccine development is the high diversity (>200) of M-types, which are divided in 48 clusters and two clades (X and Y) based on sequence similarity and host proteins binding capacities. GAS virulence is, in part, due to an array of surface and secreted proteins interfering with the human complement and coagulation systems. A Whole Blood Killing Assay (WBKA) is traditionally performed to monitor GAS survival rate in human blood collected on heparin. However, heparin is well-known to directly interact with human coagulation and complement systems through binding of fibrinogen and C4BP respectively.
Methods: We have performed paired-WBKA with an array of representative M-types in heparinized and hirudinized blood from several donors and compared the survival of the strains by calculating the fold change in growth (FC).
Results: Clade Y strains survive better or grow equally in heparinized blood compared to hirudinized blood while clade X strains seem to be killed in heparinized blood unlike in hirudinized blood. This killing was shown to be phagocytes and complement dependent.
Conclusions: Understanding the mechanism behind those phenotypes could bring a new perspective on GAS virulence and should also encourage WBKA standardization.