<unk> , or<unk> eumococcus, is a Gram-positive, alpha-hemolytic, facultative anaerobic member of the genus Streptococcus. A significant human pathogenic bacterium,<unk>  was recognized as a major cause of<unk> eumonia in the late 19th century, and is the subject of many humoral immunity studies.<unk>  resides asymptomatically in the nasopharynx of healthy carriers. The respiratory tract, sinuses, and nasal cavity are the parts of host body that are usually infected. However, in susceptible individuals, such as elderly and immunocompromised people and children, the bacterium may become pathogenic,<unk> read to other locations and cause disease. <unk>  is the main cause of community acquired<unk> eumonia and meningitis in children and the elderly, and of septicemia in HIV-infected persons. The methods of transmission include sneezing, coughing, and direct contact with an infected person.
Despite the name, the organism causes many types of<unk> eumococcal infections other than<unk> eumonia.  These invasive<unk> eumococcal diseases include bronchitis, rhinitis, acute sinusitis, otitis media, conjunctivitis, meningitis, bacteremia, sepsis, osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, cellulitis, and brain abscess.<unk>  is one of the most common causes of bacterial meningitis in adults and young adults, along with Neisseria meningitidis, and is the leading cause of bacterial meningitis in adults in the USA. It is also one of the top two isolates found in ear infection, otitis media.<unk> eumococcal<unk> eumonia is more common in the very young and the very old.
It also is a major bacterium for invasive diseases like<unk> eumonia and meningitis in South Asian children 12 years of age, though the evidence is of low quality and scarce.<unk>  can be differentiated from Streptococcus viridans, some of which are also alpha-hemolytic, using an optochin test, as<unk>  is optochin-sensitive.<unk>  can also be distinguished based on its sensitivity to lysis by bile, the so-called "bile solubility test". The encapsulated, Gram-positive coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci. They have 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.
Streptococcus pneumoniae
Haemophilus influenzae
Neisseria meningitidis
Streptococcus pyogenes
Haemophilus influenzae biogroup aegyptius
Rhodococcus equi
Chlamydophila pneumoniae
Moraxella catarrhalis