Pneumococcal refers to Pneumococcus, which is another name for Streptococcus pneumoniae; a species of Gram-positive, lancet-shaped diplococci frequently occurring in chains; cells are readily lysed by bile salts. Virulent forms are enclosed in type-specific polysaccharide capsules; there is also a specific somatic antigen (M protein) for each of the approximately 85 types, and somatic C carbohydrate common to all types. They are normal inhabitants of the respiratory tract, and are perhaps the most common causative agents of meningitis, sinusitis, and other infections.

of or derived from or caused by bacteria of the genus pneumococcus