A 68-year-old male patient with 3rd degree burn wounds affecting 25% TBSA was admitted in the hospital and treated with intravenous fluids and analgesics. After 8 days of hospital admission, the patient develops fever and leukocytosis. On examination, there is erythema and swelling around the wound. Exudate from this wound is positive for gram negative, oxidase positive bacilli, which does not ferment sugars. Culture is shown below. Drug of choice for this infection is: -