Gut microbiota-driven BCAA biosynthesis via Staphylococcus aureus -expressed acetolactate synthase impairs glycemic control in type 2 diabetes in South China

An increase in branched-chain amino acid (BCAA) levels can result in insulin resistance at different stages of type 2 diabetes (T2D), however, the causes of this increase are unclear. We performed metagenomics and metabolomics profiling in patients with prediabetes (PDM), newly diagnosed diabetes (NDDM), and post-medication type 2 diabetes (P2DM) to investigate whether altered gut microbes and metabolites could explain the specific clinical characteristics of different disease stages of T2D. Here we identify acetolactate synthase (ALS) a BCAA biosynthesis enzyme in Staphylococcus aureus as a cause of T2D insulin resistance. Compared with healthy peoples, patients with PDM, NDDM, and P2DM groups, especially in P2DM group, have increased faecal numbers of S. aureus. We also demonstrated that insulin administration may be a risk factor for S. aureus infection in T2D. The presence of ALS-positive S. aureus correlated with the levels of BCAAs and was associated with an increased fasting blood glucose (FBG) and insulin resistance. Humanized microbiota transplantation experiment indicated that ALS contributes to disordered insulin resistance mediated by S. aureus. We also found that S. aureus phage can reduced the FBG levels and insulin resistance in db/db mice. The ALS-positive S. aureus are associated with insulin resistance in T2D, opening a new therapeutic avenue for the prevention or treatment of diabetes.