**Core Concept**
Meningitis is an infection of the meninges, the protective membranes surrounding the brain and spinal cord. In children, particularly under the age of 2, the most common cause of meningitis is a bacterial infection. The causative organism depends on the age of the child, with certain pathogens more prevalent in specific age groups.

**Why the Correct Answer is Right**
In infants under 1 year of age, the most common cause of bacterial meningitis is *Neisseria meningitidis* (also known as meningococcus). This bacterium is highly contagious and can be spread through respiratory droplets, such as those produced by coughing or sneezing. The pathogenesis of meningococcal meningitis involves the bacterium's ability to invade the bloodstream and cross the blood-brain barrier, leading to inflammation of the meninges.

**Why Each Wrong Option is Incorrect**
**Option A:** *Streptococcus pneumoniae* is a common cause of bacterial meningitis, but it is more commonly seen in older children and adults. While it can cause meningitis in infants, it is not the most common cause in this age group.
**Option B:** *Haemophilus influenzae* type b (Hib) was a leading cause of meningitis in children before the widespread use of Hib conjugate vaccines. Although vaccination has significantly reduced its incidence, it is still a possible cause in unvaccinated children, but not the most common in this age group.
**Option C:** *Escherichia coli* (E. coli) can cause meningitis, particularly in neonates, but it is not the most common cause in 1-year-old children.

**Clinical Pearl / High-Yield Fact**
It's essential to consider the age and vaccination status of the child when evaluating a suspected case of bacterial meningitis. The most common causes of meningitis can vary depending on these factors, and prompt identification of the causative organism is crucial for effective treatment and prevention of complications.

**Correct Answer:** C. *Escherichia coli*