A patient of post-cholecystectomy biliary stricture has undergone an ERCP three days ago. Following this she has developed acute cholangitis. Which of the following is the most likely organism causing acute cholangitis?
**Core Concept**
Acute cholangitis is a bacterial infection of the biliary tract, often caused by gram-negative bacteria. The liver's bile ducts can become infected after a procedure like ERCP, especially if there is a stricture or stenosis.
**Why the Correct Answer is Right**
In the setting of a post-cholecystectomy biliary stricture, the most likely organism causing acute cholangitis is **Escherichia coli** (E. coli). E. coli is a gram-negative rod that commonly colonizes the gut and can easily infect the biliary tract, especially in the presence of a stricture or stenosis. This is due to the increased pressure and stasis of bile, which facilitates bacterial growth and infection.
**Why Each Wrong Option is Incorrect**
* **Option A:** Staphylococcus aureus is more commonly associated with skin and soft tissue infections, as well as endocarditis, rather than biliary tract infections.
* **Option B:** Klebsiella pneumoniae is another gram-negative rod that can cause urinary tract infections and pneumonia, but it is less commonly associated with biliary tract infections.
* **Option D:** Pseudomonas aeruginosa is a gram-negative rod that can cause a variety of infections, including respiratory and urinary tract infections, but it is not the most likely organism causing acute cholangitis.
**Clinical Pearl / High-Yield Fact**
In patients with biliary tract disease, especially after an ERCP, it's essential to empirically treat with broad-spectrum antibiotics that cover gram-negative bacteria, such as E. coli, until culture results are available.
**Correct Answer: C. Escherichia coli**