Regulatory rewiring confers serotype-specific hyper-virulence in the human pathogen group A Streptococcus

Area of Science:

• Microbiology
• Pathogen Biology
• Molecular Genetics

Background:

• Phenotypic variation among pathogen isolates influences disease.
• Specific group A Streptococcus (GAS) serotypes are linked to distinct disease outcomes.
• Serotype M3 GAS is frequently associated with severe invasive infections.

Purpose of the Study:

• Investigate the genetic factors contributing to the severe invasive potential of M3 GAS.
• Determine the role of the orphan kinase RocA in M3 GAS pathogenesis.
• Elucidate the molecular mechanisms by which RocA influences GAS virulence.

Main Methods:

• RNA sequencing (RNAseq) to analyze gene expression in M3 GAS with a rocA null mutant.
• In vitro assays to assess bacterial survival against human phagocytic killing.
• In vivo murine bacteremia model to evaluate M3 GAS virulence.
• Genetic manipulation (complementation, mutation) to study RocA and CovR/S interactions.

Main Results:

• The natural rocA null mutant allele in M3 GAS significantly enhances the expression of numerous immunomodulatory virulence factors.
• M3 GAS isolates with the rocA mutation exhibited 13-fold greater survival against human phagocytes compared to complemented strains.
• The rocA mutation in M3 GAS led to significantly increased virulence in a murine bacteremia model.
• RocA was found to regulate the CovR/S two-component system, as RocA activity requires functional CovR/S, and RocA influences CovR phosphorylation levels.

Conclusions:

• The absence of functional RocA kinase in M3 GAS is a key factor potentiating severe invasive infections.
• RocA acts upstream of or interfaces with the CovR/S two-component system to control virulence factor expression.
• Loss of RocA function in M3 GAS promotes enhanced bacterial survival and pathogenicity, contributing to disease severity.