Streptococcus agalactiae
Streptococcus agalactiae Gram-staining
Streptococcus agalactiae beta-hemolytic colonies
Cultural characteristics
Biochemical characters
Phylum Firmicutes, Class Bacilli, Order Lactobacillales, Family Streptococcaceae, Genus Streptococcus, Streptococcus agalactiae
Lehmann and Neumann 1896.
Streptococcus difficilis (corrig. Eldar et al. 1995) Kawamura et al. 2005. Old synonyms: Streptoccocus de la mammite  
Nocard & Mollereau 1887,
Streptococcus agalactiae contagiosae  Kitt 1893, Streptococcus mastitidis  Migula 1900.

Lancefield group B. Cross-reaction may be encountered with group G streptococci.
Gram-positive 0.6-1.2 μm cocci, nonmotile, grouped in long chains.
Beta-hemolytic colonies, although some bovine and fish isolates were not hemolytic
S. difficile strains), sometimes alpha-hemolytic. CAMP-positive. Non-pigmented, but
may be encountered yellow, orange, or brick-red pigmented colonies. Pigment
production may be enhanced by addition of starch to the medium or by anaerobic
Grows at 37 ºC, no growth at  45 ºC; variable at 10 ºC. Aerobic, facultatively anaerobic.
Growth on complex media: Trypticase soy agar with defibrinated sheep blood.
Brain-hearth infusion broth. Many strains can grow in media containing 40% bile.
Isolated from  human (urogenital tract, intestine) & animal sources (bovine, cats, dogs,
rats, hamsters and also from frogs and fish).
Meningitis, septicaemia, arthritis, urinary infections & neonatal sepsis (serotypes I,
II, III, and V) in humans. Wound infections, cellulitis, fasciitis, endocarditis, and
osteomyelitis may occur. Usually is a member of the normal flora of the female
urogenital tract and rectum.
Bovine mastitis.Some endocarditis and dermatitis in dogs were reported. Formerly
Streptococcus difficile strains cause meningitis in fish (Tilapia sp. & Oncorhynchus
  1. 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.
  2. Holt J.G., Krieg N.R., Sneath P.H.A., Staley J.T. and Williams S.T., 1994. Bergey's Manual of Determinative Bacteriology, Ninth
    Edition, Williams & Wilkins, A Waverly Company, Baltimore, pp 527-558.
  3. Facklam R (October 2002). "What happened to the streptococci: overview of taxonomic and nomenclature changes". Clin.
    Microbiol. Rev. 15 (4): 613–30.
  4. Lehmann K.B. & Neumann R.: Atlas und Grundriss der Bakteriologie und Lehrbuch der speziellen bakteriologischen Diagnostik,
    1st ed., J.F. Lehmann, München, 1896.
  5. Kawamura Y., Itoh Y., Mishima N., Ohkusu K., Kasai H. & Ezaki T.: High genetic similarity of Streptococcus agalactiae and
    Streptococcus difficilis: S. difficilis Eldar et al. 1995 is a later synonym of S. agalactiae Lehmann and Neumann 1896 (Approved
    Lists 1980). Int. J. Syst. Evol. Microbiol., 2005, 55, 961-965.
Positive results for arginine dihydrolase, Voges-Proskauer, alkaline phosphatase,
hydrolysis of hippurate, acidification of N-acetyl-glucosamine, glucose, glycerol (only
aerobically fermented), galactose, maltose,  ribose (weak), trehalose (weak at 24
hours, but positive at 48 hours incubation - admin note) & saccharose.

Negative results for esculin, gelatin & starch hydrolysis, pyrrolidonyl arylamidase,
beta-galactosidase, acidification of: amygdalin, arbutin, arabitol, arabinose, dulcitol,
erythritol, inulin, mannitol, melibiose, melezitose, raffinose, sorbitol, sorbose & xylose.

Variable results for alpha-galactosidase, beta-glucuronidase, fermentation of lactose,
cellobiose & salicin.
(c) Costin Stoica
Culture media
Biochemical tests
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