**Core Concept**
The question is testing the student's knowledge of neonatal meningitis, specifically the clinical presentation and cerebrospinal fluid (CSF) findings associated with this condition. The correct answer requires an understanding of the typical CSF profile and the common pathogens responsible for neonatal meningitis.

**Why the Correct Answer is Right**
The baby's clinical presentation of fever and leukocytosis, along with the CSF findings of pleocytosis, increased protein, and decreased glucose, is consistent with bacterial meningitis. The presence of gram-positive rods in the CSF is a key clue, as this morphology is characteristic of Listeria monocytogenes. Listeria monocytogenes is a common cause of neonatal meningitis, particularly in premature infants, and is known to cause a CSF profile with increased protein and decreased glucose. The bacteria can enter the CSF through the bloodstream and cause inflammation, leading to the observed symptoms.

**Why Each Wrong Option is Incorrect**
* **Option A:** Escherichia coli (E. coli) is a common cause of neonatal meningitis, but it typically presents with gram-negative rods in the CSF, not gram-positive rods.
* **Option B:** Group B Streptococcus (GBS) is a common cause of neonatal sepsis and meningitis, but it typically presents with gram-positive cocci in chains, not gram-positive rods.
* **Option D:** 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**
Listeria monocytogenes is a foodborne pathogen that can cause neonatal meningitis, particularly in premature infants. It is essential to consider Listeria in the differential diagnosis of neonatal meningitis, especially in the presence of gram-positive rods in the CSF.

**Correct Answer:** D. Listeria monocytogenes.