What causes pneumococcal infection?

Updated: Jun 08, 2020
  • Author: Eduardo Sanchez, MD; Chief Editor: John L Brusch, MD, FACP  more...
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S pneumoniae is an encapsulated, gram-positive, catalase-negative cocci that grows as a facultative anaerobe. These organisms often appear on Gram stain as lancet-shaped diplococci that grow in chains (see image below). On blood and chocolate agar plates, a green zone (alpha-hemolysis; due to the breakdown of hemoglobin by pneumolysin) surrounds the colonies. Other identifying properties include sensitivity to optochin (which distinguishes it from other alpha-hemolytic streptococci) and bile solubility.

Sputum Gram stain from a patient with a pneumococc Sputum Gram stain from a patient with a pneumococcal pneumonia. Note the numerous polymorphonuclear neutrophils and gram-positive, lancet-shaped diplococci. Courtesy of C. Sinave, MD, personal collection.

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