## **Core Concept**
The patient's presentation of an exquisitely tender prostate gland suggests a diagnosis of acute bacterial prostatitis. This condition is typically caused by a bacterial infection that inflames the prostate gland. The most common pathogens responsible for this infection are usually gram-negative bacteria.

## **Why the Correct Answer is Right**
The correct answer, **Escherichia coli (E. coli)**, is the most common cause of acute bacterial prostatitis. *E. coli* is a gram-negative rod that is commonly found in the urinary tract and can easily infect the prostate, especially in the setting of urinary reflux or stasis. The bacteria can ascend from the urethra or rectum to the prostate. *E. coli* accounts for approximately 70-80% of cases of acute bacterial prostatitis.

## **Why Each Wrong Option is Incorrect**
- **Option A: Klebsiella pneumoniae** - While *Klebsiella pneumoniae* can cause urinary tract infections and prostatitis, it is less common than *E. coli*.
- **Option B: Pseudomonas aeruginosa** - This organism is more commonly associated with infections in immunocompromised individuals or those with specific exposures (like contaminated water) and is not the most common cause of acute bacterial prostatitis in the general population.
- **Option D: Staphylococcus saprophyticus** - This gram-positive coccus is more commonly associated with urinary tract infections, particularly in sexually active young women, and is not the most common cause of acute bacterial prostatitis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that acute bacterial prostatitis often presents with symptoms such as fever, chills, and pain in the lower back, perineum, or radiating to the penis or testicles, along with urinary symptoms like frequency, urgency, and dysuria. Digital rectal examination (DRE) reveals a tender, swollen, and warm prostate gland.

## **Correct Answer:** . Escherichia coli