Which two organisms are most commonly associated with bacterial meningitis in adults and older children?

• A. Streptococcus pneumoniae and Neisseria meningitidis
• B. Haemophilus influenzae and Listeria monocytogenes
• C. Streptococcus pyogenes and Staphylococcus aureus
• D. Escherichia coli and Listeria monocytogenes

Answer: (A)

The main idea is identifying the two organisms that most often cause bacterial meningitis in adults and older children. Streptococcus pneumoniae is the leading cause in this group; it’s an encapsulated gram-positive diplococcus that frequently colonizes the nasopharynx and can invade the meninges, leading to inflammation. Vaccination against its capsule has reduced its incidence, reinforcing its prominent role. Neisseria meningitidis is also a major player, especially in children and adolescents; it’s a gram-negative diplococcus spread by close contact and can cause outbreaks, with vaccines targeting several serogroups.

Together, these two pathogens account for the majority of meningitis cases in this age range. Other organisms listed tend to be more relevant in different contexts: Haemophilus influenzae type b was more common before widespread Hib vaccination; Listeria monocytogenes is more typical in older adults or immunocompromised individuals and in neonates; Escherichia coli is a leading cause in neonates; Streptococcus pyogenes and Staphylococcus aureus can cause meningitis but are less common primary pathogens in healthy adults and older children.