The two most common pathogens causing neonatal meningitis are which?

• A. Group B Streptococcus and Escherichia coli
• B. Streptococcus pneumoniae and Neisseria meningitidis
• C. Listeria monocytogenes and Staphylococcus aureus
• D. Haemophilus influenzae type b and Pseudomonas aeruginosa

Answer: (A)

Neonatal meningitis is mainly caused by organisms tied to the maternal birth canal, so the most frequent culprits are Group B Streptococcus and Escherichia coli. Group B Streptococcus commonly colonizes the mother’s vagina and rectum; during labor, the baby can be exposed and develop bacteremia that seeds the meninges, especially in early-onset disease. Escherichia coli, especially strains with the K1 capsule, also colonizes the maternal and neonatal GI tract and can invade the CNS after bacteremia. The neonate’s immature immune system makes CNS invasion more likely once bacteria are in the bloodstream, which is why these two pathogens dominate neonatal meningitis.

Other organisms listed are more typical of meningitis in older children or adults (like Streptococcus pneumoniae and Neisseria meningitidis) or are less common causes in neonates (such as Listeria monocytogenes, Staphylococcus aureus, Haemophilus influenzae type b, or Pseudomonas).