**Core Concept**
Hydrocephalus is a condition characterized by an accumulation of cerebrospinal fluid (CSF) in the brain, leading to increased intracranial pressure. A ventriculoperitoneal shunt is a medical device used to drain excess CSF from the brain to the abdomen. Infection of the shunt, also known as shunt-related ventriculitis, is a serious complication that can occur if bacteria contaminate the shunt system.

**Why the Correct Answer is Right**
The most common organism isolated from shunt-related infections is **Staphylococcus epidermidis**. This coagulase-negative staphylococcus is a skin commensal that can colonize medical devices, including shunts. The organism's ability to form biofilms on the surface of the shunt tubing makes it particularly resistant to antibiotic treatment. The infection typically presents with symptoms such as fever, headache, and signs of increased intracranial pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Escherichia coli** is a gram-negative rod that is commonly found in the gastrointestinal tract. While it can cause infections in the central nervous system, it is not the most likely organism to be isolated from a shunt-related infection.
* **Option B:** **Streptococcus pneumoniae** is a gram-positive coccus that is a common cause of bacterial meningitis. However, it is not typically associated with shunt-related infections.
* **Option C:** **Haemophilus influenzae** is a gram-negative rod that was previously a common cause of meningitis and other infections in children. However, with the widespread use of conjugate vaccines, its incidence has decreased significantly.

**Clinical Pearl / High-Yield Fact**
Shunt-related infections are often caused by skin commensals that colonize the shunt tubing during surgery or device manipulation. Early recognition and treatment of these infections are critical to prevent long-term sequelae and neurological damage.

**Correct Answer:** B. **Staphylococcus epidermidis**.