Choice A rationale:

Haemophilus influenzae type b (Hib) was a common cause of bacterial meningitis in the past, especially in children, but its incidence has significantly decreased due to the widespread use of the Hib vaccine.

Choice B rationale:

Neisseria meningitidis (meningococcal) can cause meningitis and is an important pathogen, but it is more commonly associated with meningitis in children and young adults.

Choice C rationale:

Streptococcus pneumoniae (pneumococcal) is the most common cause of bacterial meningitis in adults. It is a gram-positive bacterium that can lead to severe infections, including pneumonia, meningitis, and bloodstream infections.

Choice D rationale:

Escherichia coli is a bacterial species typically associated with urinary tract infections and gastrointestinal illnesses. While it can rarely cause meningitis in certain populations, it is not the most common cause of bacterial meningitis in adults.

Choice E rationale:

Group B streptococcus is a significant cause of neonatal meningitis but is less commonly responsible for meningitis in adults.