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Group A streptococcal infections are a number of infections with Streptococcus pyogenes, a group A streptococcus (GAS). [1] S. pyogenes is a species of beta-hemolytic Gram-positive bacteria that is responsible for a wide range of infections that are mostly common and fairly mild. If the bacteria enters the bloodstream, the infection can become ...
However, both Streptococcus dysgalactiae and the Streptococcus anginosus group can possess group A antigen as well. Group A streptococci, when grown on blood agar, typically produce small (2–3 mm) zones of beta-hemolysis, a complete destruction of red blood cells. The name group A (beta-hemolytic) Streptococcus is thus also used. [1]
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Similarly, group B streptococcus typically denotes Streptococcus agalactiae, although minor beta-hemolytic group B streptococci like S. troglodytidis exist. [15] While most streptococcal illnesses in humans originate from species adapted to humans, such as S. pneumoniae or S. pyogenes, there are zoonotic species capable of causing infections. [15]
Streptococci are chains of cocci such as Streptococcus pyogenes. Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus). Tetrads are clusters of four cocci arranged within the same plane such as Micrococcus sp.). Sarcina describes a pack-like cuboidal arrangement of eight cocci such as Sarcina ventriculi.
S. agalactiae, or group B streptococcus, GBS, causes pneumonia and meningitis in newborns and the elderly, with occasional systemic bacteremia. Importantly, Streptococcus agalactiae is the most common cause of meningitis in infants from one month to three months old.
Staphylococci are usually opaque, [1]: 167–8 while many Streptococcus species are translucent. [4]: 188 The overall shape of the colony may be characterized as circular, irregular, or punctiform (like pinpoints). The vertical growth or elevation of the colony, another identifying characteristic, is assessed by tilting the agar plate to the ...
Streptococcal pharyngitis, also known as streptococcal sore throat (strep throat), is pharyngitis (an infection of the pharynx, the back of the throat) caused by Streptococcus pyogenes, a gram-positive, group A streptococcus. [9] [10] Common symptoms include fever, sore throat, red tonsils, and enlarged lymph nodes in the front of the neck.