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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 ...
Chains of S. pyogenes bacteria (orange) at 900× magnification Gram stain of Streptococcus pyogenes. Unlike most bacterial pathogens, S. pyogenes only infects humans. Thus, zoonotic transmission from an animal (or animal products) to a human is rare. [8] S. pyogenes typically colonizes the throat, genital mucosa, rectum, and skin. Of healthy ...
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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]
The genus Streptococcus has around 129 species and 23 subspecies [16] that benefit many microbiomes on the human body. There are many species that show non-pathogenic characteristics; however, there are some, like S. pneumoniae , that exhibit pathogenic characteristics in the human body.
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.
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.
Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick layer of peptidoglycan in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.