A 52-year-old man from Mumbai with diabetes mellitus type 2 (HbA1c 9.2%) presents with fever (38.8°C), right flank pain, and dysuria for 3 days. Urinalysis shows pyuria, bacteriuria, and WBC casts. Blood culture and urine culture are sent. Serum creatinine is 1.8 mg/dL (baseline 1.0). Renal ultrasound shows right hydronephrosis without obstruction. Blood pressure is 100/65 mmHg. Which of the following organisms is MOST likely responsible, and what is the most appropriate initial management?