As a strict human pathogen, Streptococcus pyogenes (group A Streptococcus, or GAS) causes a wide range of infections, from superficial to life-threatening diseases, upon dissemination. Thus, it is necessary to gain a better understanding of how GAS successfully overcomes host-mediated challenges and infects various host niches. We previously identified subcutaneous fitness (scf) genes in the clinically relevant wild-type (WT) GAS M1T1 5448 strain that are critical for fitness during murine soft-tissue infection at both 24 h and 48 h postinfection. The uncharacterized locus scfCDE was transcribed as an operon and is predicted to encode an ABC importer for nutrient uptake (e.g., amino acids). Individual scfCDE deletion mutants grew comparably to WT 5448 in rich medium but exhibited reduced fitness during competitive growth in murine soft tissue and in nutrient-limiting chemically defined medium (CDM). A deletion of the permease gene scfD resulted in a monoculture growth defect in CDM that could be rescued by addition of excess peptides, suggesting a role as an amino acid importer. Interestingly, the ΔscfC substrate-binding and ΔscfD permease mutants, but not the ΔscfE ATPase mutant, were highly attenuated in murine soft tissue. Moreover, all three genes were required for GAS survival in human blood, indicating their impact is not limited to superficial infections. As such, scfCDE plays an integral role in enhancing GAS adaptation during localized infection as well as dissemination to deeper host environments. Since scfCDE is conserved throughout Firmicutes, this work may contribute to the development of therapeutic strategies against GAS and other Gram-positive pathogens.

The transport and metabolism of glucose has been shown to have far reaching consequences in the transcriptional profile of many bacteria. As glucose is most often the preferred carbon source for bacteria, its presence in the environment leads to the repression of many alternate carbohydrate pathways, a condition known as carbon catabolite repression (CCR). Additionally, the expression of many virulence factors is also dependent on the presence of glucose. Despite its importance, little is known about the transport routes of glucose in the human pathogen Streptococcus pyogenes. Considering that Streptococcus pyogenes is an important human pathogen responsible for over 500,000 deaths every year, we characterized the routes of glucose transport in an effort to understand its importance in GAS pathogenesis. Using a deletion of glucokinase (ΔnagC) to block utilization of glucose imported by non-PTS pathways, we determined that of the two glucose transport pathways in GAS (PTS and non-PTS), the non-PTS pathway played a more significant role in glucose transport. However, the expression of both pathways is linked by a currently unknown mechanism, as blocking the non-PTS uptake of glucose reduces ptsI (EI) expression. Similar to the effects of the deletion of the PTS pathway, lack of the non-PTS pathway also leads to the early activity of Streptolysin S. However, this early activity did not adversely or favorably affect survival of ΔnagC in whole human blood. In a subcutaneous murine infection model, ΔnagC-infected mice showed increased lesion severity at the local site of infection; although, lesion size and dissemination from the site of infection was similar to wild type. Here, we show that glucose transport in GAS is primarily via a non-PTS pathway. The route of glucose transport differentially affects the survival of GAS in whole human blood, as well as the lesion size at the local site of infection in a murine skin infection model.

Streptococcus pyogenes (Group A Streptococcus, GAS), a major human-specific pathogen, relies on efficient nutrient acquisition for successful infection within its host. The phosphotransferase system (PTS) couples the import of carbohydrates with their phosphorylation prior to metabolism and has been linked to GAS pathogenesis. In a screen of an insertional mutant library of all 14 annotated PTS permease (EIIC) genes in MGAS5005, the annotated ß-glucoside PTS transporter (bglP) was found crucial for GAS growth and survival in human blood and was validated in another M1T1 GAS strain, 5448. In 5448, bglP was shown to be in an operon with a putative phospho-ß-glucosidase (bglB) downstream and a predicted antiterminator (licT) upstream. Using defined non-polar mutants of the ß-glucoside permease (bglP) and ß-glucosidase enzyme (bglB) in 5448, we showed that bglB, not bglP, was important for growth in blood. Furthermore, transcription of the licT/blgPB operon was found to be repressed by glucose and induced by the ß-glucoside salicin as the sole carbon source. Investigation of the individual bglP and bglB mutants determined that they influence in vitro growth in the ß-glucoside salicin; however, only bglP was necessary for growth in other non-ß-glucoside PTS sugars such as fructose and mannose. Additionally, loss of BglP and BglB suggests they are important for the regulation of virulence-related genes that control biofilm formation, SLS-mediated hemolysis, and localized ulcerative lesion progression during subcutaneous infections in mice. Thus, our results indicate that the ß-glucoside PTS transports salicin and its metabolism can differentially influence GAS pathophysiology during soft tissue infection.

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