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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]
That is the main reason it is now used in bacteriology for the differentiation of Streptococcus pneumoniae, which is optochin-sensitive, from the other, resistant alpha-hemolytic streptococci, sometimes called the viridans streptococci because of the green colouration on blood agar around colonies.
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]
The effectiveness of individual antibiotics varies with the anatomical site of the infection, the ability of the antibiotic to reach the site of infection, and the ability of the bacteria to resist or inactivate the antibiotic. [34] Specimens for antibiotic sensitivity testing are ideally collected before treatment is started. [1]
Hemolyses of Streptococcus spp. (left) α-hemolysis (S. mitis); (middle) β-hemolysis (S. pyogenes); (right) γ-hemolysis (non-hemolytic, S. salivarius) Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms.
Streptococcus dysgalactiae is a gram positive, beta-haemolytic, coccal bacterium belonging to the family Streptococcaceae.It is capable of infecting both humans and animals, but is most frequently encountered as a commensal of the alimentary tract, genital tract, or less commonly, as a part of the skin flora.
Other strains of streptococci can cause subacute endocarditis as well. These include streptococcus intermedius, which can cause acute or subacute infection (about 15% of cases pertaining to infective endocarditis). [7] Enterococci from urinary tract infections and coagulase negative staphylococci can also be causative agents. [5]
Streptococcus cristatus is a species of viridans Streptococcus with tufted fibrils, first isolated from the human oral cavity and throat. The type strain is strain CR311 (= NCTC 12479). The type strain is strain CR311 (= NCTC 12479).