Background: Group A Streptococcus (GAS) drives inflammation through the coordinated expression of virulence factors, including the cysteine protease SpeB. SpeB activity is essential for establishing skin infections by cleaving bacterial and host proteins, resulting in dissemination and disease progression. Growth phase, pH, and nutrients are important in regulating SpeB. The host defense peptide LL-37 also regulates SpeB and determines whether expression is on or off, through the two-component system CovRS. Neutrophils undergo inflammatory cell death and are a main source of LL-37 release during GAS infections. While in vitro expression is well characterized, dynamics of SpeB regulation remain unclear within these inflammatory environments.
Methods: Complementary genetics and fluorometry techniques were used to examine SpeB regulation during infection with neutrophils collected from healthy donors. SpeB expression was characterized during infections with wild-type and knockout strains of CovRS using flow cytometry. Furthermore, SpeB regulatory patterns were characterized in vivo using a neutrophil depleted mouse intradermal infection model.
Results: In the presence of neutrophils, SpeB expression is mediated by host inflammatory pathways. Flow cytometry data confirms these results during intradermal infections. Further, depleting neutrophils during intradermal infections alters SpeB regulatory patterns within the population. The molecular mechanisms dependent on inflammation were identified using CovRS knockout strains.
Conclusions: These results suggest host inflammation plays a key role in SpeB activity during GAS infections. Further, SpeB regulation is much more complex than previously suggested, pinpointing key drivers associated with GAS induced inflammation that leads to morbidity associated with invasive infections and antibiotic failure.