Abstract
Streptococcus pyogenes (group A streptococcus [GAS]) is a human-restricted pathogen with a range of clinical manifestations and worldwide prevalence. The GAS Rgg2/Rgg3 quorum-sensing (QS) system, a cell-to-cell communication network, modifies the cell surface, resulting in increased lysozyme resistance, biofilm formation, and expression of the qim operon which is responsible for modulation of innate immune responses in macrophages. The operon encodes 10 genes with predicted homology to enzymes involved in bacterial cell surface-associated carbohydrate and teichoic acid biosynthesis pathways. Comparing extracts of GAS cell wall polysaccharides between wild type and operon mutants showed that QS-induced genes modify the S. pyogenes cell surface by adding a wall teichoic acid-like N-acetylglucosamine-linked ribitol (GlcNAc-Rbo) moiety. A fluorescently labeled phage receptor-binding protein, RBP-13-GFP, that recognizes GlcNAc-decorated ribitol phosphate repeats, bound to the GAS surface only when qim expression was induced. Deletion of the qim operon eliminated RBP-13-GFP binding, diminished bacterial colonization, and significantly attenuated GAS pathogenesis in a murine skin infection model. These findings indicate that GAS has evolved a strategy to evade innate immune response by presenting a previously unknown carbohydrate moiety upon QS.IMPORTANCEStreptococcus pyogenes is a major human pathogen, responsible for diverse clinical manifestations of both superficial and invasive infections, and can lead to post-infection sequelae like rheumatic heart disease, whose prevalence on a global scale rivals that of the most serious pathogens. Invasive S. pyogenes infections are currently on the rise worldwide, notably correlating with increasing pediatric cases of scarlet fever and enhancing the concern for long-term complications. There is much that remains unknown about S. pyogenes virulence and pathogenicity, and studies focused on understanding basic systems regulating virulence factors could lead to better therapeutics and translational research. We show here one such example, where a bacterial communication system regulating a virulence mechanism relevant to in vivo infection confers the ability to alter the host's innate immune response. We find that modifications to the cell wall arise when this virulence system is activated, which has a direct role in host-pathogen interactions. Further research into this system could provide a mechanism for disruption and serve to treat S. pyogenes infection.