The leading cause of sepsis and meningitis in newborns is which organism?

• A. Escherichia coli
• B. Streptococcus agalactiae
• C. Listeria monocytogenes
• D. Staphylococcus aureus

Answer: (B)

Group B Streptococcus (Streptococcus agalactiae) is the leading cause of neonatal sepsis and meningitis because it commonly colonizes the maternal vagina and rectum and can be transmitted to the baby during delivery. When a newborn acquires this organism, it can invade the bloodstream and meninges, leading to sepsis and meningitis in the first days of life. A helpful lab clue is the CAMP test, where GBS produces enhanced beta-hemolysis when grown with Staphylococcus aureus, creating a distinctive arrowhead pattern. Clinically, this is why prenatal screening late in pregnancy and intrapartum antibiotics for colonized mothers or those with risk factors have dramatically reduced early-onset neonatal disease. While other organisms like E. coli and Listeria monocytogenes can cause neonatal infections, they are not more common causes than GBS, and Staphylococcus aureus is not the primary agent of neonatal sepsis or meningitis.