<unk><unk> , or pneumococcus, is a Gram-positive, alpha-hemolytic diplococcus bacterium and a member of the genus<unk> . A significant human pathogen, S.<unk>  was recognized as a major cause of<unk> in the late 19th century and is the subject of many humoral immunity studies.
Despite the name, the organism causes many types of<unk>  other than<unk>  including acute sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, cellulitis, and brain abscess.
S.<unk>  is the most common cause of bacterial meningitis in adults and children, and is one of the top two isolates found in otitis media. Pneumococcal<unk> is more common in the very young and the very old.
S.<unk>  can be differentiated from<unk>  viridans, which is also alpha hemolytic, using an optochin test, as S.<unk>  is optochin sensitive. The encapsulated, gram-positive coccoid bacteria have a distinctive morphology on gram stain, the so-called, "lancet shape." It has a polysaccharide capsule that acts as a virulence factor for the organism; 91 different capsular types are known, and these types differ in virulence, prevalence, and extent of drug resistance.
Streptococcus pneumoniae infection
Haemophilus influenzae infection
Pneumococcal infections
Middle East respiratory syndrome coronavirus infection
Group B streptococcal infection
Group A streptococcal infection
COVID-19-associated neutrophilia
Lemierre's syndrome