Streptococcus pneumoniae

A Gram-positive bacterium that commonly colonizes the human upper respiratory tract and can cause pneumonia, meningitis, and other infections. Its polysaccharide capsule is a major determinant of virulence and defines many vaccine-targeted types.

Polysaccharide capsule: A bacterial surface layer made of repeating sugar molecules that can protect cells and shape host interactions. The capsule helps pneumococci evade immune clearance and distinguishes vaccine-targeted serotypes.
Pneumococcal conjugate vaccine: A vaccine that links pneumococcal capsular polysaccharides to carrier proteins to produce an immune response effective in young children. It prevents disease from selected serotypes and can reduce carriage and transmission.
Streptococcus pyogenes: A Gram-positive group A streptococcus that causes diseases including strep throat, scarlet fever, and skin infections. It is another major human pathogen in the same genus, but differs in its diseases and defining traits.
Otitis media: Inflammation or infection of the middle ear, especially common in children. Pneumococci are a frequent bacterial cause of this noninvasive infection.
Pneumococcal serotype: A classification of Streptococcus pneumoniae based on the antigenic structure of its polysaccharide capsule. Capsular variation changes immune recognition and determines which types vaccines target.
Pneumococcal polysaccharide vaccine: A vaccine made from purified capsular polysaccharides of multiple Streptococcus pneumoniae serotypes. Unlike conjugate vaccines, it stimulates a weaker immune response in young children and has limited effects on carriage.
Streptococcus agalactiae: A group B streptococcus that can cause severe infections in newborns and invasive disease in adults. It shares the genus but is especially associated with perinatal transmission rather than pneumococcal respiratory carriage.
Sinusitis: Inflammation of the tissue lining the paranasal sinuses, sometimes caused by bacterial infection. Pneumococcus can cause acute bacterial sinusitis after colonizing the upper respiratory tract.
Nasopharyngeal colonization: The presence and growth of microorganisms in the upper part of the throat behind the nose. Pneumococci usually establish carriage here before transmission or spread into normally sterile sites.
Pneumococcal antimicrobial resistance: Reduced susceptibility of Streptococcus pneumoniae to one or more antimicrobial drugs. Resistance can constrain treatment choices, especially where resistant strains are common.

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