A 35-year-old woman presents to the clinic with a 3-day history of dysuria, increased urinary frequency, and lower abdominal pain. She denies fever, chills, or flank pain. She has no significant past medical history and does not take any medications. Vital signs are temperature 37.1°C (98.6°F), blood pressure 118/72 mmHg, pulse 90 beats/min, and respirations 18/min. Physical examination is unremarkable. A urinalysis is performed and shows the following:
A urine culture grows a lactose-fermenting, urease-producing, Gram-negative rod. Imaging studies show the presence of staghorn calculi in the kidneys. Which of the following organisms is most likely responsible for this patient's urinary tract infection?
D) Proteus mirabilis
The patient's presentation with dysuria, increased urinary frequency, and lower abdominal pain, along with positive findings on urinalysis, is consistent with a urinary tract infection (UTI). The urine culture growing a lactose-fermenting, Gram-negative rod with strong urease activity, along with imaging showing staghorn calculi, strongly suggests Proteus mirabilis.
Answer choice A: Escherichia coli, is incorrect. While E. coli is the most common cause of UTIs and is a lactose-fermenting, Gram-negative rod, it does not typically lead to the formation of staghorn calculi.
Answer choice B: Enterococcus faecalis, is incorrect. Enterococcus is a Gram-positive organism and does not ferment lactose or produce strong urease activity, nor is it typically associated with staghorn calculi.
Answer choice C: Klebsiella pneumonia, is incorrect. Klebsiella is also a lactose-fermenting, Gram-negative rod and can cause UTIs but does not produce strong urease activity like Proteus mirabilis and is less commonly associated with staghorn calculi.
Answer choice E: Pseudomonas aeruginosa, is incorrect. Pseudomonas aeruginosa is a non-lactose-fermenting, Gram-negative rod and would not fit the description provided by the urine culture or the presence of staghorn calculi.
Key Learning Point
Symptoms of urinary tract infection include dysuria, increased urinary frequency, and lower abdominal pain. Urinalysis often shows positive nitrites and leukocyte esterase, along with white blood cells and bacteria. Proteus mirabilis is a lactose-fermenting, Gram-negative rod with strong urease activity that is associated with development of staghorn calculi.
