A 73-year-old nursing home resident is seen by the staffing physician due to complaints of flank pain and bleeding upon urination for the past 2 days. Medical history includes hypertension, Alzheimer dementia, and recurrent episodes of pyelonephritis. In the past 3 months, she has received antibiotics on six different occasions to treat urinary tract infections. Her vitals are temperature 39° C (102.2° F), blood pressure 90/70 mmHg, heart rate 95 beats/min, and respirations 25/min. Urinary analysis shows 2+ blood, 3+ WBCs, 3+ bacteria and pH 8.2. Abdominal x-ray reveals a large radio-opaque structure that obstructs the renal pelvis and calyces.

Which of the following organisms is the most likely etiologic agent?

• A) Enterobacter aerogenes
• B) Escherichia coli
• C) Kelbsiella ozanae
• D) Proteus mirabilis
• E) Salmonella typhi