Diabetes mellitus promotes the nasal colonization of high virulent Staphylococcus aureus through the regulation of SaeRS two-component system

Diabetic foot infections are a common complication of diabetes. Staphylococcus aureus is frequently isolated from diabetic foot infections and commonly colonizes human nares. According to the study, the nasal microbiome analysis revealed that diabetic patients had a significantly altered nasal microbial composition and diversity. Typically, the fasting blood glucose (FBG) level had an impact on the abundance and sequence type (ST) of S. aureus in diabetic patients. We observed that highly virulent S. aureus ST7 strains were more frequently colonized in diabetic patients, especially those with poorly controlled FBG, while ST59 was dominant in healthy individuals. S. aureus ST7 strains were more resistant to human antimicrobial peptides and formed stronger biofilms than ST59 strains. Critically, S. aureus ST7 strains displayed higher virulence compared to ST59 strains in vivo. The dominance of S. aureus ST7 strains in hyperglycemic environment is due to the higher activity of the SaeRS two-component system (TCS). S. aureus ST7 strains outcompeted ST59 both in vitro, and in nasal colonization model in diabetic mice, which was abolished by the deletion of the SaeRS TCS. Our data indicated that highly virulent S. aureus strains preferentially colonize diabetic patients with poorly controlled FBG through SaeRS TCS. Detection of S. aureus colonization and elimination of colonizing S. aureus are critical in the care of diabetic patients with high FBG.

The effects of L-arginine on protein stability and DNA binding ability of SaeR, a transcription factor in Staphylococcus aureus

The SaeRS two-component system in Staphylococcus aureus controls the expression of a series of virulence factors, such as hemolysins, proteases, and coagulase. The response regulator, SaeR, belongs to the OmpR family with an N-terminal regulatory domain and a C-terminal DNA binding domain. To improve the production and stability of the recombinant protein SaeR, l-arginine (L-Arg) was added to the purification buffers. L-Arg enhanced the solubility and stability of the recombinant protein SaeR. The thermal denaturation temperature of SaeR in 10 mM L-Arg buffer was significantly increased compared to the buffer without L-Arg. Microscale Thermophoresis (MST) analysis results showed that the SaeR protein could bind to the P1 promoter under both phosphorylated and non-phosphorylated status in buffer containing 10 mM L-Arg. These results illustrate an effective method to purify SaeR and other proteins.