66 plus species including:


(Pyogenic Streptococci)

(Oral Streptococci)

(Lactic Streptococci)

(Anaerobic Streptococci)

(Other Streptococci)

The genus Melissococcus contains an organism previously known as Streptococcus pluton .


Gram Stain: Positive.
Morphology: Spherical, ovoid, or cocci shaped. Often occur in pairs or chains when grown in liquid media. They are sometimes elongated in the axis of the chain to form a lancelate shape.
Size: 0.5-2.0 micrometers in diameter.
Motility: Usually no motility occurs.
Capsules: Encapsulation occurs often.
Spores: None.


Streptococcal colonies vary in color from gray to whitish and usually glisten. Often dry colonies are observed. Encapsulated strains may appear mucoid. Many variations exist among Lancefield groups.


Facultatively or strictly anaerobic. Requires a nutritionally rich media for growth. Typically the metabolism is fermentative, with sugars being metabolized without gas. For Streptococcus spp. the main product of carbohydrate fermentation is dextrorotatory lactic acid.


As well as phenotypic biochemical reactions, some of the streptococci can also be identified by their carbohydrate antigens (Lancefield groups A to P, excluding I) and by their protein antigens M and T (Griffiths types 1-30).

Lancefield grouping may be required for accurate identification of some species. (1)


Many species exist as commensals or parasites on man and other animals, mainly inhabiting the mouth and upper respiratory tract. Streptococci are found on the mucous membranes of the mouth, respiratory, alimentary and genitourinary tracts, and the skin of man and animals (including insects). They are also present in milk and dairy products, in some food and plant material, soil and fecally contaminated water. Some species are saprophytic in their natural environments.


Group A streptococci represent one of the most impressive human pathogens. (8) The numerous virulence factors of S. pyogenes allow it to produce a wide array of serious infections including tonsillitis, respiratory infection, skin (impetigo, erysipelas) and soft tissue infections. Pharyngitis, as well as scarlet fever, toxic shock, necrotizing fasciitis, erysipelas and other spreading infections, and two serious poststreptococcal sequelae, rheumatic fever and glomerulonephritis are indicated in the staphylococci clinical isolates. Causative agent of endocarditis in some mammals, including humans. Often associated with food poisoning and septicemias, meningitis, sinusitis, as well as mastitis in cattle.

Group B streptococci are an important cause of neonatal infection characterized by sepsis and meningitis. Group B streptococcal infections include diabetes mellitus, cancer, and human immunodeficiency virus infection. Adult group B infections include bacteremia, endocarditis, skin and soft tissue infection, and osteomyelitis.

Other isolates, those belonging to non-group A or B streptococci, can cause a wide range of infections such as bacteremia, endocarditis, meningitis, septic arthritis, and infections of the respiratory tract and skin. Notable species include S . pneumoniae , S. bovis , Viridans streptococci, and nutritionally variant streptococci.


For culture: Tryptic Soy Agar or Blood Agar 5% (Sheep blood), Chocolate Agar, or Chocolate with Pyridoxal.
For selective isolation: Columbia CNA Agar, Rose Agar, Selective Strep Agar, or FB Broth.
For maintenance: Blood Agar 5% for routine maintenance. Brucella with 20% Glycerol or Skim Milk for long-term storage at -70 degrees C. Lyophilization may be used for preservation.


Temperature: 25-45 degrees C., Optimum temperature at 37 degrees C. (Some strains demonstrate typical hemolysis when incubated anaerobically).
Mixed flora specimens incubation temperature - 35 degrees C. for 18 hours (not under CO 2 ).
Time: Up to 48 hours.
Atmosphere: Aerobic; some strains require increased CO 2 (5-10%) for optimum growth.
Anaerobic streptococci must be incubated anaerobically.


1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.

8. Howard, B.J., et al. 1994. Clinical and Pathogenic Microbiology , 2nd ed. Mosby, St. Louis, IL.