Final answer:
Group B Streptococcus (Streptococcus agalactiae or GBS) is the most common cause of neonatal meningitis, which is notable in babies up to 3 months old and can be passed from mother to newborn during birth.
Step-by-step explanation:
The most common cause of neonatal meningitis, which is meningitis occurring in babies up to 3 months of age, is Group B Streptococcus (Streptococcus agalactiae or GBS). This encapsulated gram-positive bacterium can be found in the urogenital and gastrointestinal microbiota of about 10-30% of humans, and it is capable of causing meningitis in individuals of all ages. GBS is commonly found in the microbiota of the vagina and gastrointestinal tract and has the potential to be transmitted to newborns from the mother either before or during birth, leading to neonatal meningitis.
Diagnosis of neonatal meningitis is often confirmed by positive results from cultures of cerebrospinal fluid (CSF) or blood, and it is typically treated with ß-lactam antibiotics like intravenous penicillin or ampicillin, often in combination with gentamicin. Although it receives prompt medical attention, there is still a significant mortality rate associated with neonatal meningitis, underscoring the seriousness of the infection in this vulnerable population.