**Core Concept**
Neonatal meningitis is a severe infection that affects the meninges, the protective membranes surrounding the brain and spinal cord, in newborns. It is often caused by bacterial pathogens that are transmitted from the mother or acquired during delivery.

**Why the Correct Answer is Right**
Group B Streptococcus (GBS) is the most common cause of neonatal meningitis, responsible for approximately 50% of cases. GBS is a gram-positive bacterium that is typically found in the gastrointestinal and genitourinary tracts of healthy adults. During childbirth, GBS can be transmitted to the newborn through the birth canal, leading to infection. The bacteria can then invade the meninges, causing inflammation and infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Escherichia coli (E. coli) is a common cause of neonatal sepsis and meningitis, but it is less commonly associated with meningitis than GBS.
**Option B:** Listeria monocytogenes is a rare cause of neonatal meningitis, typically affecting premature or immunocompromised infants.
**Option C:** Staphylococcus aureus is a common cause of skin and soft tissue infections, but it is not a typical cause of neonatal meningitis.

**Clinical Pearl / High-Yield Fact**
GBS colonization in pregnant women is a significant risk factor for neonatal meningitis, and intrapartum antibiotic prophylaxis (IAP) is recommended for women colonized with GBS to reduce the risk of transmission.

**Correct Answer: A. Group B Streptococcus**