Diabetic foot ulcers differ from non-diabetic trauma, as diabetic patients have dysfunctional wound healing owing to changes in the microcirculation. Herein, we report the case of a 48-year-old man with a 4-year history of uncontrolled type 2 diabetes. The patient had developed a 3-cm-wide ulcer deep to the phalanx on the big toe of the right foot 3 weeks ago, and the ulcer became infected with multi-drug-resistant Enterobacter cloacae 1 week later. We performed thorough wound debridement combined with Vacuum Sealing Drainage (VSD) and intravenous immunoglobulin administration without antibiotic therapy. This treatment strategy reduced the size of the ulcer. Three weeks later, antibiotic-susceptible Staphylococcus aureus was cultured from the wound tissue instead of Enterobacter cloacae, and so, the patient was administered antibiotics. The patient recovered well after this simple procedure followed by antibiotic therapy.