Group A Streptococcus (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; a phenomenon which has been 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, the host factors governing GAS biofilm formation and composition remain poorly understood.
To address this, we have established, optimised, and validated a physiologically relevant model of GAS biofilm formation in the context of skin infection. The biofilm phenotype conveyed increased resistance to neutrophil mediated killing, and reduced antibiotic sensitivity compared to planktonic GAS. Biofilm biomass, cell viability and matrix composition were assessed under specific environmental conditions selected to mimic the skin wound environment. GAS biofilm formation was found to be temperature dependant, with greater biomass and bacterial cell viability at 30°C compared to 37°C. Fluorescent staining indicated that carbohydrates were the predominant matrix component at 30°C but markedly reduced at 37°C. Additionally, confocal microscopy revealed larger and denser biofilms formed at pH 9 compared to those formed at pH 7 and pH 5.
We have established a skin relevant model of GAS biofilm formation and demonstrated that biofilm composition is dependent on host environmental conditions. Future studies will focus on identifying the specific virulence factors involved in the GAS biofilm formation.