A patient with benign hypertrophy of prostate was admitted in the hospital for 3 weeks. He subsequently developed suspected catheter associated-urinary tract infection. The tip of the catheter was sent for culture and was grown on blood agar. After 24 hours, the blood agar shows the following appearance. What is the most likely causative agent for the UTI?
A. Escherichia coli
B. Klebsiella pneumoniae
C. Proteus mirabilis
Ans: C. Proteus mirabilis
(Ref Ananthanarayan p288, 8/e p280; Jawetz 27/e p233).
- Blood agar shows concentric swarming – Seen in Proteus infections.
- More active movement with peritrichous flagella à Resulting in “swarming” on solid media.
- Swarming inhibited by chemicals (phenylethyl alcohol or CLED (cystine-lactose-electrolyte-deficient) medium.
- Shows concentric swarming on blood agar.
Note: Clostridium species show non-concentric swarming