Streptococcus pyogenes (GAS) is a Gram-positive human pathogen, causing a variety of diseases, ranging from superficial to life-threatening. Although GAS remains sensitive to penicillin, antibiotic treatment failure occurs in 20-40% of GAS infections; commonly associated with the formation of GAS biofilms. Biofilms are surface-attached microbial communities surrounded by a matrix of proteins, polysaccharides, lipids, and nucleic acids. Host environmental conditions, such as temperature and pH, are known to modulate biofilm phenotypes in a range of micro-organisms. However, host factors governing GAS biofilm formation and composition remain poorly understood.
We have established a physiologically relevant model of GAS biofilm formation in the context of skin infection. This model exhibits biofilm phenotypes including resistance to neutrophil-mediated killing and reduced antibiotic sensitivity compared to planktonic GAS. Biofilm biomass, cell viability and matrix composition were assessed under specific conditions selected to mimic the skin wound environment. GAS biofilm formation was found to be temperature and pH dependant with greater biomass observed at 30°C and pH 9 compared to 37°C and pH 7, respectively. Fluorescent staining indicated that carbohydrates were the predominant matrix component at 30°C but markedly reduced at 37°C. RNA-sequencing of GAS biofilms formed under different environmental conditions revealed alterations to oxidative phosphorylation, carbohydrate metabolism, and fatty acid biosynthesis pathways.
Herein, we demonstrate that GAS biofilm formation, matrix composition, and gene expression are dynamically regulated by environmental conditions, highlighting the influence of host stressors on biofilm adaptation.