Cat. no. A70 Selective Strep Agar, 15x100mm Plate, 17ml 10 plates/bag


Hardy Diagnostics Selective Strep Agar is a selective medium recommended for use in the primary isolation of all Streptococcus species, including streptococcal groups A (S. pyogenes), B (S. agalactiae), C, D, F, G, and S. pneumoniae, especially from repiratory specimens.


Selective Strep Agar is designed to inhibit gram-negative bacilli and staphylococci, thereby allowing for the isolation, subculture, and identification of pathogenic streptococci, including beta-hemolytic streptococci and S. pneumoniae.

Tryptic Soy Agar is the basal medium for Selective Strep Agar. Organic nitrogen, particularly amino acids and long-chained peptides are supplied by the combination of casein and soy peptones. This combination renders the medium highly nutritious. Osmotic equilibrium is maintained by sodium chloride. Sheep blood (5%) has been added to facilitate growth and to detect hemolytic activity. Selective agents are added to suppress much of the oral flora, including coliforms, staphylococci, Micrococcus, Haemophilus and Neisseria species. All species of Streptococcus will grow on this medium. For the selection of only group A streptococci (S. pyogenes) see Group A Beta Strep Agar, Cat. no. A72.


Ingredients per liter of deionized water:*

Pancreatic Digest of Casein 15.0gm
Peptic Digest of Soybean Meal 5.0gm
Sodium Chloride 5.0gm
Nucleic Acid 3.0gm
Selective Agents 15.3mg
Sheep Blood 50.0ml
Agar 15.0gm

Final pH 7.3 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.


Storage: Upon receipt store at 2-8ºC. away from direct light. Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), hemolysis, contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.



Specimen Collection: Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport media and refrigerated until inoculation. Consult listed references for information on specimen collection.(1-5)

Prepared media should be inoculated, incubated, and results recorded according to accepted procedures described in the listed reference texts.(1-5)

Method of Use: Medium should be brought to room temperature prior to inoculation. Inoculate according to standard microbiological procedures. Streak inoculum so as to obtain isolated colonies. Stab the medium several times with the inoculating loop in the area of heavy inoculation in order to create anaerobic conditions to stimulate maximum expression of beta-hemolysis. Incubate at 35ºC. for 18-24 hours.

It is recommended to incubate plates either anaerobically or with increased CO2 (5-10%) in order to enhance the development of hemolytic zones of the pathogenic streptococci.(7)

Square Pill Pocket Plate: After inoculation, place one CO2 tablet in the pill pocket and place plate in a sealed zip bag. Do not invert the plate. Proceed with incubation parameters as outlined above.


Selective Strep Agar is designed to grow all species of streptococci, which would include some normal respiratory flora, such as Streptococcus viridans.

Arcanobacterium haemolyticum may be recovered on Selective Strep Agar, however the colonies will likely be obscured by other flora, thus Arcanobacterium Selective Agar (Cat. no. A134) is recommended for A. haemolyticum recovery.

Unless a provision is made to reduce oxygen tension, approximately 2% of group A streptococci may be missed if incubated aerobically. It is recommended that several stabs be made into the medium upon inoculation.(2) Incubation in increased CO2 or anaerobically is recommended.

Either anaerobic incubation or aerobic with stabs (see Method of Use) is the preferable atmosphere.(6)

Selective Strep Agar may be inhibitory to certain rare strains of streptococci.


Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Streptococcus pyogenes
ATCC® 19615
A 24hr 35°C CO2** Growth; beta-hemolysis
Streptococcus pneumoniae
ATCC® 6305
A 24hr 35°C CO2** Growth; alpha-hemolysis
Escherichia coli
ATCC® 25922
B 24hr 35°C CO2** Inhibited
Staphylococcus epidermidis
ATCC® 12228
B 24hr 35°C CO2** Inhibited

** Atmosphere of incubation is enriched with 5-10% CO2.

User Quality Control


Selective Strep Agar should appear opaque, and cherry red in color.

S. pyogenes growing on Selective Strep Agar

Streptococcus pyogenes (ATCC® 19615) colonies growing on Selective Strep Agar (Cat. no. A70). Incubated in CO2 for 24 hours at 35ºC.

S. pneumoniae growing on Selective Strep Agar

Streptococcus pneumoniae (ATCC® 6305) colonies growing on Selective Strep Agar (Cat. no. A70). Incubated in CO2 for 24 hours at 35ºC.

E. coli inhibited on Selective Strep Agar

Escherichia coli (ATCC® 25922) growth inhibited on Selective Strep Agar (Cat. no. A70). Incubated in CO2 for 24 hours at 35ºC.


1. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

2. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

5. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

6. The United States Pharmacopeia , XXII, 1990.

7. Pacifico, L., et al. 1995. Journal of Clinical Micro., 33; 9:2480-2482. American Society for Microbiology.

ATCC is a registered trademark of the American Type Culture Collection.