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When alpha-hemolysis (α-hemolysis) is present, the agar under the colony is light and greenish. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha-hemolysis. This is sometimes called green hemolysis because of the color change in the agar.
Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. [2] Cell division in streptococci occurs along a single axis , thus when growing they tend to form pairs or chains, which may appear bent or twisted.
The viridans streptococci are a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), although some species in this group are actually γ-hemolytic, meaning they produce no change on blood agar. [1]
Clinical identification of beta-hemolytic streptococci relies on culturing the bacteria with agar media that has been supplemented with blood. [2] This method allows for beta-hemolysis to be easily identified, which is a critical step in further identification tactics. [2]
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 ...
The name group A (beta-hemolytic) Streptococcus is thus also used. [ 1 ] The species name is derived from Greek words meaning 'a chain' ( streptos ) of berries ( coccus [Latinized from kokkos ]) and pus ( pyo )-forming ( genes ), since a number of infections caused by the bacterium produce pus.
Lysis of these cells releases heme into the surroundings, allowing the bacteria to take up the free iron. But hemolysin is related to bacteria not only in this way but also in some others. [citation needed] As mentioned before, hemolysin is a potential virulence factor produced by microorganisms, which can put a human's health at risk.
Bacteria of the genus Enterococcus, formerly known as group D streptococci, were classified as members of the genus Streptococcus until 1984 and are included in the original Lancefield grouping. [4] Many—but not all—species of streptococcus are beta-hemolytic .