**Core Concept**
Neonatal bacterial meningitis is a severe infection in newborns caused by bacteria, which can lead to significant morbidity and mortality. The most common causative agents are typically those that are acquired from the maternal genital tract during birth.

**Why the Correct Answer is Right**
Group B Streptococcus (GBS) is the most common cause of neonatal bacterial meningitis, accounting for approximately 50-70% of cases. GBS is a gram-positive bacterium that can colonize the maternal genital tract, and transmission to the newborn can occur during delivery. The bacteria can then invade the central nervous system, leading to meningitis. The exact mechanism of GBS invasion is not fully understood, but it is thought to involve the bacterium's ability to adhere to and invade epithelial cells.

**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 common than GBS.
* **Option B:** Listeria monocytogenes is a rare cause of neonatal meningitis, typically seen in premature infants or those with underlying immunodeficiency.
* **Option C:** Staphylococcus aureus is a common cause of skin and soft tissue infections, but it is not typically associated with neonatal meningitis.

**Clinical Pearl / High-Yield Fact**
GBS colonization in pregnant women can be identified through routine screening at 35-37 weeks of gestation. Women who test positive can receive intrapartum antibiotic prophylaxis to reduce the risk of transmission to the newborn.

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