Species associated with pneumonia and other pyogenic infections, Streptococcus pneumoniae appears in fresh material as a pair of oval cocci with their long axes in line; capsules are present. On culture, chains of more rounded cocci may grow, and cap-sularity is often lost. Serum or blood is an aid to isolation, and on blood agar an alpha type of haemolysis may cause confusion with Streptococcus viridans, resolved by the inclusion in or on the medium of optochin (ethylhydrocupreine hydrochloride) to which the viridans are insensitive but by which the pneumococcus are inhibited. Over 70 serotypes of the organism are known, their specificity being dependent on capsular antigens of polysaccharide variety, identified by agglutination, or by swelling of the capsules when the strain is immersed in its homologous serum. The organism is virulent to mice, and very sensitive to most antibiotics.
A species that occurs in pairs with capsules, is also called the pneumococcus, and may be part of the transient flora of the upper respiratory tract. Based on capsular chemistry, more than 80 serological types have been identified. It is the causative agent of certain types of pneumonia, esp. lobar pneumonia, and is associated with other infectious diseases such as meningitis, conjunctivitis, endocarditis, periodontitis, septic arthritis, osteomyelitis, otitis media, septicemia, spontaneous bacterial peritonitis, and, rarely, urinary tract infections. About 40,000 people die of pneumococcal disease each year in the U.S., more than from any other vaccine-preventable illness.
Also known as Pneumococcus, this variety of Streptococcus bacterium has the capacity to lead to pneumonia as well as other grave conditions like meningitis and septicemia.