**Core Concept**
The CAMP (Christie-Atkins-Munch-Peterson) test is a screening method used to identify bacteria that produce a hemolysin, which causes a characteristic "double zone of hemolysis" around bacterial colonies. This test is specifically used to differentiate between Group B Streptococcus (GBS) and other Streptococcus species.

**Why the Correct Answer is Right**
The positive CAMP test in an infant with neonatal meningitis indicates the presence of Group B Streptococcus (GBS). GBS produces a hemolysin that enhances the hemolytic activity of the CAMP factor, resulting in a characteristic double zone of hemolysis. This bacterium is a common cause of neonatal meningitis and sepsis, and its identification is crucial for guiding antibiotic therapy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Group A Streptococcus (GAS) does not produce the CAMP factor and would not result in a positive CAMP test.
**Option B:** This option is incorrect because Escherichia coli (E. coli) is not a Streptococcus species and would not produce a positive CAMP test.
**Option C:** This option is incorrect because Klebsiella pneumoniae is a different type of bacterium that does not produce the CAMP factor and would not result in a positive CAMP test.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that a positive CAMP test in a neonate with meningitis strongly suggests Group B Streptococcus as the causative agent. This bacterium requires specific antibiotic therapy, and prompt identification is critical for improving outcomes.

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