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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]
Species of streptococci are classified based on their hemolytic properties. [10] Alpha-hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Beta-hemolytic species cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood ...
The system, created by Rebecca Lancefield, was historically used to organize the various members of the family Streptococcaceae, which includes the genera Lactococcus and Streptococcus, but now is largely superfluous due to explosive growth in the number of streptococcal species identified since the 1970s. [2]
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. Other synonymous terms are incomplete hemolysis and partial hemolysis.
Streptococcus mitis is a species of Gram-positive, mesophilic, alpha-hemolytic bacteria in the genus Streptococcus, belonging to the viridans streptococci group. These bacteria are facultative anaerobes, and made up of non-motile and non-sporing cocci (round cells) that are catalase negative.
Streptococcus oralis is a Gram positive viridans streptococcus of the Streptococcus mitis group. [2] [3] S. oralis is one of the pioneer species associated with eubiotic dental pellicle biofilms, and can be found in high numbers on most oral surfaces. [4] [5] It has been, however, found to be an opportunistic pathogen as well. [2]
The group is named after a principal member species, Streptococcus anginosus. The older name Streptococcus milleri (as well as Streptococcus milleri group, SMG) is now pseudotaxonomic, as the idea that these streptococci constituted a single species was incorrect. The anginosus group streptococci are members of the viridans streptococci group. [1]
Viridans may refer to: Viridans streptococci, large group of bacteria species; Achatinella viridans, species of mollusc; Aerococcus viridans, species of bacteria;