Inclusion Criteria:  1. Surface skin cotton swab collection  (1) Observation group: In the endocrinology department of Nanfang hospital, the patient were diagnosed with type 2 diabetes to the WHO 1999 diagnostic criteria for diabetes.  (2) Control group:  Control subjects that was ruled out diabetes according to the WHO 1999 diagnostic criteria for euglycemia. Age ≥18 years, the patient and (or) his family members know and agree to participate in this study.  2. Skin tissue collection  (1) Observation group:  The patient was diagnosed with type 2 diabetes in the Endocrinology Department, Burns Department, Traumatology Orthopedics, Plastic Surgery in Nanfang hospital. Patients who need surgical operations such as debridement and amputation below the knee joint due to various reasons such as diabetic foot osteomyelitis, fractures, car accidents and so on.  (2) Control group:  The patient without type 2 diabetes in the Endocrinology Department, Burns Department, Traumatology Orthopedics, Plastic Surgery in Nanfang hospital. Patients who need surgical operations such as debridement and amputation below the knee joint due to various reasons such as post-traumatic foot osteomyelitis, fractures, car accidents and so on. Age ≥18 years, the patient and (or) his family members know and agree to participate in this study.  Exclusion Criteria:  The patients Including other skin diseases, using medically prescribed soap for bathing, using cosmetics on the feet, suffering from severe liver and kidney disease, immune system disease, HIV infection, malignant tumors, or using immunosuppressive drugs within the first four weeks. The patient or (and) their family members refused to participate in this study.  The researchers judged that they are not suitable to participate in this research.