A urine sample of a patient suspected to have urinary tract infection(UTI) was sent to the microbiology lab. On culture, the colony shows hemolysis on blood agar, on eosin methylene blue (EMB) agar the following is seen, a positive indole test, and a positive MUG test. The most likely etiologic organism is
## **Core Concept**
The question involves identifying a urinary tract infection (UTI) pathogen based on specific microbiological test results. The key tests mentioned are hemolysis on blood agar, appearance on eosin methylene blue (EMB) agar, a positive indole test, and a positive MUG (4-methylumbelliferyl-β-D-glucuronide) test. These tests help differentiate bacteria commonly causing UTIs.
## **Why the Correct Answer is Right**
The correct answer, **E. coli**, is indicated by the combination of test results provided:
- **Hemolysis on blood agar**: Some E. coli strains can exhibit hemolysis.
- **Appearance on EMB agar**: E. coli typically appears as colonies with a metallic sheen on EMB agar due to lactose fermentation.
- **Positive indole test**: E. coli is usually indole-positive, which helps in its identification.
- **Positive MUG test**: E. coli is MUG-positive, meaning it can hydrolyze MUG to produce a fluorescent compound. This is a key characteristic used in the identification of E. coli, especially in urine cultures.
## **Why Each Wrong Option is Incorrect**
- **Option A:** *Klebsiella pneumoniae* can cause UTIs but typically does not produce indole and may not show the same level of hemolysis or MUG positivity as E. coli.
- **Option B:** *Staphylococcus saprophyticus* is a common cause of UTIs, especially in sexually active young women, but it does not match the biochemical profile described (e.g., it would not be MUG-positive).
- **Option C:** *Proteus mirabilis* can cause UTIs and may show hemolysis, but it is usually urease-positive (which is not mentioned) and does not match the MUG and indole test results provided.
- **Option D:** This option is not provided, implying we focus on the characteristics aligning with **E. coli**.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **E. coli** is the most common cause of urinary tract infections, especially in outpatients, and its identification can often be streamlined in the lab by using a combination of EMB agar, the indole test, and the MUG test. The MUG test is particularly useful because it allows for rapid identification of E. coli.
## **Correct Answer:** .