Bacterial meningitis is commonly caused by which organism?

Bacterial meningitis is commonly caused by which organism?

• A. Streptococcus
• B. Staphylococcus aureus
• C. Pseudomonas aeruginosa
• D. Listeria monocytogenes

Answer: (A)

Streptococcus pneumoniae is the organism most commonly responsible for bacterial meningitis. This pneumococcus is a Gram-positive diplococcus that often colonizes the nasopharynx and can invade the bloodstream to reach the meninges. Its polysaccharide capsule helps it resist immune clearance, contributing to its prominence as a cause of meningitis across age groups, especially in adults and older children. In meningitis, CSF typically shows a neutrophilic predominance with high protein and low glucose, reflecting bacterial infection. While other bacteria matter in specific contexts—Staphylococcus aureus more with neurosurgical or healthcare-associated cases, Pseudomonas aeruginosa in some hospital-acquired scenarios, and Listeria monocytogenes in neonates, the elderly, or immunocompromised—the pneumococcus remains the most common culprit overall.

Streptococcus pneumoniae is the organism most commonly responsible for bacterial meningitis. This pneumococcus is a Gram-positive diplococcus that often colonizes the nasopharynx and can invade the bloodstream to reach the meninges. Its polysaccharide capsule helps it resist immune clearance, contributing to its prominence as a cause of meningitis across age groups, especially in adults and older children. In meningitis, CSF typically shows a neutrophilic predominance with high protein and low glucose, reflecting bacterial infection. While other bacteria matter in specific contexts—Staphylococcus aureus more with neurosurgical or healthcare-associated cases, Pseudomonas aeruginosa in some hospital-acquired scenarios, and Listeria monocytogenes in neonates, the elderly, or immunocompromised—the pneumococcus remains the most common culprit overall.