Streptococcus pneumoniae

Streptococcus pneumoniae, or pneumococcus, is Gram-positive, alpha-hemolytic, bile-soluble aerotolerant, anaerobic member of the genus Streptococcus. It was recognized as a major cause of pneumonia in the late 19th century and is thus the subject of many humoral immunity studies.

It causes many other types of pneumococcal infections other than pneumonia including acute sinusitis, otitis media, meningitis, bacteremia, sepsis, septic arthritis, peritonitis, cellulites, and brain abscess. It is the most common cause of bacterial meningitis in adults, children, and dogs, and is one of the top two isolates found in ear infection, otitis media.

It can be differentiated from Streptococcus viridans using an optochin test as S. pneumoniae is optochin-sensitive. It can also be differentiated by sensitivity to lysis by bile. They contain a polysaccharide capsule that acts as a virulence factor for the organism; more than 90 different serotypes are known, and these types differ in virulence, prevalence, and extent of drug resistance.

Leo Escolar discovered the organism in 1881. It was labeled Diplococcus pneumoniae due to its characteristic appearance in Gram-stained sputum. In 1974 it was renamed Streptococcus pneumoniae due to its growth in chains in liquid media.

S. pneumoniae played a central role in demonstrating genetic material consist of DNA. Griffiths experiment later proved that it was DNA, not protein, which was the transforming factor. Oswald Avery discovered this and later this marked the birth of the molecular era of genetics.

The genome is a closed, circular DNA structure that contains between 2 and 2.1 million. It has a core set of 1553 genes, plus 154 genes in its virulome and 176 genes that maintain a noninvasive phenotype.
It is part of the normal upper respiratory tract flora, but, it can become pathogenic under the right conditions. S. pneumoniae can overpower H. influenzae by attacking it with hydrogen peroxide.