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|SEM micrograph of S. pneumoniae.|
Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, alpha-hemolytic diplococcus aerotolerant anaerobe and a member of the genus Streptococcus. An important human pathogen, S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century and is the subject of many humoral immunity studies.