Streptococcus anginosus- An Overview


Streptococcus anginosus is a Gram-positive bacterium that belongs to the anginosus group of viridans streptococci, which also includes Streptococcus intermedius and Streptococcus constellatus. These bacteria are part of the normal human flora that colonize the mouth, upper respiratory tract, gastrointestinal tract, and vagina. However, they can also cause various infections of the oral and non-oral sites, especially in immunocompromised individuals or those with underlying conditions.

S. anginosus was first isolated and identified by Andrewes and Horder in 1906 from the human gut. The species name ‘anginosus‘ is taken from the term ‘angina’, indicating the association between the species and the disease angina, causing chest pain due to lack of oxygen to the muscles. S. anginosus is sometimes also referred to as Streptococcus milleri, but this name is now pseudotaxonomic as it was based on the erroneous assumption that all members of the anginosus group belonged to a single species.

S. anginosus is a facultative anaerobe that can grow in air with 5% carbon dioxide or under anaerobic conditions. It can produce acetoin from glucose, ferment lactose, trehalose, salicin, and sucrose, and hydrolyze esculin and arginine. It can also produce hydrogen sulfide (H2S) from cysteine, which is a unique feature among streptococci and contributes to its pathogenicity. S. anginosus may be alpha-hemolytic, beta-hemolytic, or non-hemolytic on blood agar, and some strains may produce a distinct butterscotch or caramel odor.

S. anginosus has several virulence factors that enable it to adhere to host cells, evade phagocytosis, destroy extracellular matrix components, and form abscesses. These include adhesins, capsule, H2S production, and hydrolytic enzymes. S. anginosus is associated with various infections such as bacteremia, endocarditis, brain abscesses, liver abscesses, pulmonary infections, intra-abdominal infections, osteomyelitis, prosthetic joint infections, and soft tissue infections. Some studies have also suggested a link between S. anginosus and colorectal carcinoma or abscesses.

The diagnosis of S. anginosus infections is based on the isolation and identification of the organism from clinical specimens using morphological, cultural, biochemical, and molecular methods. The treatment of S. anginosus infections depends on the site and severity of infection, but penicillin, ampicillin, erythromycin, and tetracycline are usually effective against most strains. In some cases, surgical drainage or removal of infected tissue may be required.