Streptococcus pneumoniae

Microbiology

• Gram-positive, lancet-shaped diplococci
• 90+ serotypes, based on capsular polysaccharide that is bound to peptidoglycan
• Lab identification is based on α-hemolysis of blood agar (from pneumolysin), optochin susceptibility, and bile salt solubility

Epidemiology

• Present worldwide
• Major cause of morbidity and mortality in children
  • Leading cause of under-5 mortality worldwide

Pathophysiology

• Acquired by coughing and sneezing
• Asymptomatic carriage or colonization in the nasopharynx
• Invasion through epithelial cells into the bloodstream, using the PAF and pIg receptors
• Capsule and various proteins help it to evade immune system