Group B Streptococcus (Streptococcus agalactiae) is the most common cause of neonatal bacterial meningitis beyond one week of age.

Step-by-Step Justification:

Group B Streptococcus (GBS) and Neonatal Infections:

GBS is a leading cause of late-onset neonatal meningitis (occurring after 7 days of age)​.

Infection typically occurs through vertical transmission from the mother or postnatal exposure.

Neonatal Risk Factors:

Premature birth, prolonged rupture of membranes, and maternal GBS colonization increase risk​.

Why Other Options Are Incorrect:

A. Group A: Rare in neonates and more commonly associated with pharyngitis and skin infections.

C. Group C: Typically associated with animal infections and rarely affects humans.

D. Group D: Includes Enterococcus, which can cause neonatal infections but is not the most common cause of meningitis.

CBIC Infection Control References:

APIC Text, "Group B Streptococcus and Neonatal Meningitis"​.