Streptococcus milleri is an unofficial name applied to a group of basically similar viridans streptococci species showing various hemolytic, serological, and physiological characteristics. The species name Streptococcus anginosus has recently been recognized as the approved name for these organisms. They have been implicated as etiologic agents in a variety of serious purulent infections, but because of their heterogeneous characteristics, these organisms may be unrecognized or misidentified by clinical laboratorians. The unique characteristic of them from other pathogenic streptococci, such as S. pyogenes and S. agalactiae, is their ability to cause abscesses.
These non-hemolytic viridans streptococci were first described by Guthof in 1956 after being isolated from dental abscesses. He named these organisms "Streptococcus milleri" in honor of the microbiologist W. D. Miller.
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