Streptococcus mitis
Streptococcus mitis cells, Gram stained
Streptococcus mitis on Sheep blood agar. Colonies
after 24h (A) and 72h (B) incubation
Taxonomy
Morphology
Cultural characteristics
Biochemical characters
Ecology
Pathogenicity
References
Phylum Firmicutes, Class Bacilli, Order Lactobacillales, Family Streptococcaceae, Genus Streptococcus, Streptococcus mitis  
Andrewes and Horder 1906. Two biovars were described.

Lancefield group O (biovar 1), K or non-groupable*.
*Admin note: a Streptococcus mitis biovar 1 strain isolated from human throat presented Lancefield group G antigens.
Gram-positive cocci, 0.6-0.8 μm in diameter, arranged in pairs or chains, non-motile.
S-type, sometimes R-type colonies, alpha-hemolytic. Rarely mucoid colonies may
occur or colonies resembling broken glass. Facultatively anaerobic, growth at 37.0 ºC.
Growth at 45 ºC is variable. Growth on : trypticase soy agar with defibrinated sheep /
horse blood, brain heart infusion broth. Most strains may require some factors from
yeast extract for growth.
Isolated from human saliva, sputum, dental plaque and feces. Isolated from oral
cavity of a man with parodontosis, as dominant microflora (admin note). Another
strain was isolated from human throat (admin note).
Oral and pharynx normal inhabitant. May cause septicaemia, endocarditis or
meningitis in immunosuppressed organisms.
  1. Andrewes F.W. & Horder T.J.: A study of the streptococci pathogenic for man. Lancet, 1906, 2, 708-713.
  2. Elliott, John A., Burke, John P., Classen, David C., Ford, Clyde D., Evershed, Sherri, Aloia, Mary R., Wilfahrt, James K.: Streptococcus
    mitis sepsis in bone marrow transplant patients receiving oral antimicrobial prophylaxis. American Journal of Medicine, 1990.
  3. Balkundi, Dhruv R.; Murray, Dennis; Patterson, Maria; Gera, Renuka; Scott-Emuakpor, Ajovi, Ph.D.; Kulkarni, Roshni M.D.: Penicillin-
    Resistant Streptococcus mitis as a Cause of Septicemia with Meningitis in Febrile Neutropenic Children.
  4. Robert A. Whiley and Jeremy M. Hardie, 2009. Genus I. Streptococcus Rosenbach 1884, 22AL. In: (Eds.) P.D. Vos, G. Garrity, D.
    Jones, N.R. Krieg, W. Ludwig, F.A. Rainey, K.-H. Schleifer, W.B. Whitman. Bergey’s Manual of Systematic Bacteriology, Volume 3:
    The Firmicutes, Springer, 655-711.
Positive results for leucine aminopeptidase, chymotrypsin, alanyl-phenylalanyl-proline
arylamidase, valine aminopeptidase, alpha-D-glucosidase, N-acetyl-beta-D-
glucosaminidase, acid production from: fructose, galactose, glucose, lactose,
mannose
, and sucrose.

Negative results for catalase, esculin hydrolysis, hippurate hydrolysis, pyrrolid
one
arylamidase, beta-glucuronidase, Voges-Proskauer reaction, acid  production from:
amygdalin, arabinose, arabitol, arbutin, cyclodextrin, dulcitol, esculin, glycerol,
glycogen, mannitol, methyl D-glucoside, D-melezitose, rhamnose, L-sorbose, starch,
tagatose
, and xylose.

Variable reaction for alkaline phosphatase, acid phosphatase, arginine hydrolysis,
phosphoamidase, alpha-glucosidase, alpha-maltosidase, beta-D-fucosidase,
beta-glucosaminidase, glycyl-tryptophan-arylamidase, alpha- and beta-D-
galactosidases, lactosidase, phospho-beta-galactosidase, sialidase, acid production
from: D-cellobiose, inulin, maltose, melibiose, pullulan,  D-raffinose, ribose, salicin,
sorbitol
, and D-trehalose (biovar 1 was able to ferment trehalose more often).
(c) Costin Stoica
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Legend:  '+' = more than 85% positive; '-'  = more than 85% negative; v = variable (16-84% positive).
 
Beta-
glucosaminidase
Beta-
lactosidase
Phospho-beta-galactosidase
Alpha-
galactosidase
Beta-
galactosidase
Beta-
glucosidase
Biovar 1
-
-
-
v
v
-
Biovar 2
+
v
v
+
+
v
Differential characters of Streptococcus mitis biovars:
 
Arginine hydrolysis
Starch
hydrolysis
Sorbitol
fermentation
Maltose
fermentaion
Melibiose
fermentation
Raffinose
fermentation
Biovar 1
-
v
-
v
v
v
Biovar 2
+
+
v
+
+
+