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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]
However, it has retained some clinical usefulness even after the taxonomic changes, [1] and as of 2018, Lancefield designations are still often used to communicate medical microbiological test results. The classification assigns a letter code to each serotype. There are 20 described serotypes assigned the letters A to V (excluding E, I and J). [3]
This phenomenon is the mechanism behind the CAMP test, [2] a test that was historically used for the identification of Streptococcus agalactiae and Listeria monocytogenes. [3] A modified version of this test called the reverse CAMP test, utilizing S. agalactiae instead of S. aureus, can also be used to identify Clostridium perfringens.
Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha-hemolysis. Alpha-hemolysis is also termed incomplete hemolysis or partial hemolysis because the cell membranes of the red blood cells are left intact.
Further identification can be done serologically to test for the presence of capsular antigen, which is the dominant structure on the surface of S. pneumoniae. [2] [5] Bile solubility can be used to further distinguish S. pneumoniae from viridans streptococci as S. pneumoniae are bile soluble and viridans streptococci are not. [6]
The anginosus group streptococci are members of the viridans streptococci group. [1] 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. [ 2 ]
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 GC content of the S. sanguinis genome is 43.4% (higher than the GC contents of other streptococci). The genome encodes 2,274 predicted proteins , 61 tRNAs , and four rRNA operons . About 22% of the open reading frames are conserved hypothetical proteins (present in multiple species but having unknown functions), and approximately 645 of the ...