A 2-year-old boy is brought to the physician because of 2‐day history of musky smelling urine, irritability, and decreased appetite. He has a past medical history of a congenital ureteral stricture. He has been treated with antibiotics for recurrent urinary tract infections. in the past 6 months. Vital signs are temperature is 37.8°C (100.04°F), pulse 80 beats/min, and respirations 20/min. Physical examination shows mild suprapubic tenderness. Laboratory studies show gram-negative motile rods which are urease and nitrite test positive.
Which of following laboratory characteristics will most likely also be observed with the causal agent?
The correct answer is:
A) Catalase positive, swarming colonies on solid agar
This patient has a congenital condition that obstructs the flow of urine, predisposing him to urinary tract infections. The causative agent is gram negative and urease positive which is consistent with Proteus mirabilis. The other possible gram-negative cause would be E. coli, but that organism is urease negative.
Answer choice B: H2S negative, pink mucoviscous colonies on MacConkey agar, is incorrect. This describes Klebsiella pneumoniae.
Answer choice C: Oxidase negative, green iridescent colonies on eosin-methylene blue (EMB) agar. This describes E. coli.
Answer choice D: Oxidase negative, no growth on MacConkey agar, is incorrect. This describes Staphylococcus saprophyticus.
Answer choice E: Oxidase negative, pink colonies on MacConkey agar, is incorrect. This describes E. coli.
Key Learning Point
Proteus mirabilis is a gram-negative motile rod which is urease and nitrite positive, catalase positive, and demonstrate swarming colonies on solid agar.
