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16S rRNA RefSeq: V15.23    Genomic RefSeq: V10.1
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Streptococcus mitis (HMT-677)
Taxon Description:
Heterogenous group of viridans type of streptococci that has had taxonomic revisions. Original type strain NCTC 3165 (= SK51) clustered with Streptococcus gordonii strains. Proposed NCTC 12261 be replacement type strain of S. mitis [2]. Closely related to S. pneumoniae by 16S rRNA comparisons.

Disease Associations:
Not usually attributed to disease especially oral infections.May be involved in infective endocarditis toxic shock-like syndrome and neonatal infections. Septicemias have been reported.

Prevalence and Source:
Commonly found on most surfaces in the human oral cavity and throat [1].
species/SmitisMagenta-HparaCyan.jpg Cells of Streptococcus mitis/oralis (magenta) and Haemophilus parainfluenzae (cyan) together in dental plaque.
See Perera et al. 2021

Class: Bacilli
Order: Lactobacillales
Genus: Streptococcus
Species:Streptococcus mitis
Status: Named - Cultured
Type/Reference Strain: NCTC 12261
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Former Names or Synonyms:
Phylum: Firmicutes
16S rRNA Reference Sequences:    view in
RefSeq tree
RefSeq ID: 677_3929

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Genotypic Description:
Phenotypic Characteristics:
Facultatively anaerobic Gram positive cocci approximately 1 um in diameter that grow in short or long chains in broth cultures. Carbohydrates are femented primarily to lactic acid and no gas. Catalase negative. Cell wall contains riitol teichoic acid and minimal rhamnose. Peptidoglycan type is Lys-direct. G+C content is 41 mol%.[23]2 biovars of S. mitis differ biochemically and serologically [23]
Cultivability: Alpha-hemolytic colonies (0.7- 1.2 mm diameter) on blood agar and extensive greening on chocolate agar.
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Microbial Ecology
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NCBI Taxon ID: 28037 [Link to NCBI]
PubMed Searches:
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Number of
Genome Sequences:
216 See List
Phylogenetic Trees:
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[1] Kilian M, Mikkelsen L, Henrichsen J. Taxonomic study of viridans Streptococci: Description of Streptococcus gordonii sp. nov. and emended descriptions of S. sanguis (White and Niven 1946), S. oralis .... Int J Syst Bacteriol. 1989 Oct;39(4):471-84.
[2] Aas JA, Paster BJ, Stokes LN, Olsen I, Dewhirst FE. Defining the normal bacterial flora of the oral cavity. J Clin Microbiol. 2005 Nov;43(11):5721-32
[3] Hardie RM. Genus Streptococcus. Bergey's Manual of Systematic Bacteriology 1986; Vol. 2, pp. 1043-1063.