A 35-year-old woman presents with 4 days of dysuria and urinary frequency that has worsened over the past 24 hours to include fever, right flank pain, and chills. She has no vaginal discharge and no gastrointestinal complaints. Temperature is 38.9°C and right costovertebral angle tenderness is present. Urinalysis shows 3+ leukocyte esterase, nitrites, too-numerous-to-count white blood cells per high-power field, and WBC casts. Urine culture grows >100,000 CFU/mL of Escherichia coli.
Which of the following surface structures of the infecting organism is most responsible for establishing the infection seen in this patient?