Cat. no. C5510 CRITERION™ Cystine Tryptic Agar (CTA) 59gm
Cat. no. C5511 CRITERION™ Cystine Tryptic Agar (CTA) 500gm
Cat. no. C5512 CRITERION™ Cystine Tryptic Agar (CTA) 2kg
Cat. no. C5513 CRITERION™ Cystine Tryptic Agar (CTA) 10kg
Cat. no. C5514 CRITERION™ Cystine Tryptic Agar (CTA) 50kg


Hardy Diagnostics CRITERION™ Cystine Tryptic Agar (CTA) is recommended for the determination of carbohydrate fermentation by fastidious microorganisms, such as Neisseria spp. It is also used for the detection of bacterial motility and the base can serve as a holding medium for the maintenance of fastidious microorganisms.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.


In general, Cystine Tryptic Agar (CTA) provides a nutritious basal medium composed of casein peptones, cystine, inorganic salts, phenol red, and agar. The inorganic salts serve as a source of essential ions. Phenol red is the pH color indicator.

CRITERION™ Cystine Tryptic Agar (CTA) supplemented with a 1% concentration of a specific carbohydrate is used to detect fermentation reactions. The 1% concentration is recommended to decrease the possibility of reversal reactions. Reversion occurs when the carbohydrate is depleted, thereby resulting in the masking of acid by alkaline by-products from peptone degradation. The acid produced by carbohydrate consumption causes a decrease in pH resulting in a color shift in the medium from red-pink to yellow.

The addition of agar to the medium allows for the detection of motility along the stab line of inoculation. Motile organisms extend from the stab line and produce turbidity or cloudiness throughout the medium. Non-motile organisms grow only along the stab line and leave the surrounding medium clear.

CRITERION™ Cystine Tryptic Agar (CTA) can also be made carbohydrate-free and used as a holding medium for fastidious microorganisms at 25ºC.


Gram weight per liter: 29.5gm/L
Pancreatic Digest of Casein 20.0gm
Sodium Chloride 5.0gm
L-Cystine 0.5gm
Sodium Sulfite 0.5gm
Phenol Red 0.017gm
Agar 3.5gm

Final pH 7.3 +/- 0.2 at 25ºC.

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


Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original pink.

Store the prepared culture media at 2-8ºC.



1. Suspend 29.5gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat with frequent agitation to boiling for one minute to dissolve completely.

3. If desired, add 5-10gm (0.5-1.0%) of carbohydrate to the medium before autoclaving. Stir to mix thoroughly. Adjust the pH if necessary. (Note: Some carbohydrates are degraded by heat and should be added as described in step 4.)

4. Pour the desired volume of media into appropriately sized tubes and sterilize in the autoclave at 118ºC. for 12 minutes. As an alternative, dissolve medium in 900ml of water, autoclave, and aseptically add 100ml of sterile 5-10% carbohydrate solution.

5. Cool tubes in the upright position.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. Y11.


Only small amounts of acid may be produced by Neisseria spp., as the organisms utilize carbohydrates oxidatively.

Aerobic incubation is necessary, as incubation in CO2 may lead to erroneous results.

Lack of sufficient inoculum may lead to erroneous results.

Do not inoculate to the bottom of the tube; improper inoculation may lead to weak acid reactions, thus creating difficulty in test interpretation.

Peptone utilization results in the production of alkaline by-products. Prolonged incubation may result in a reversion reaction where alkaline by-products mask the acid by-products formed from carbohydrate utilization.

Because some strains of meningococci, primarily sulfonamide-resistant strains, do not produce acid from maltose, repeated subcultures to non-inhibitory media may be required to restore their maltose utilizing capability.

Rare strains of gonococci require additional compounds not provided by the CTA Media formulation, and will therefore not grow on the CTA Media.


Standard microbiological supplies and equipment such as autoclaves, incinerators, and incubators, etc., are not provided.


Test Organisms Inoculation Method* Incubation Results**
Time Temperature Atmosphere
CTA Dextrose :**
Listeria monocytogenes
ATCC ® 7644
E 18-48hr 15-30°C Aerobic Growth; motility (+),
acid (+)
Neisseria gonorrhoeae
ATCC ® 43069
E 18-48hr 35°C Aerobic Growth; motility (-),
acid (+)
Neisseria meningitidis
ATCC ® 13090
E 18-48hr 35°C Aerobic Growth; motility (-),
acid (+)
Branhamella ( Moraxella ) catarrhalis
ATCC ® 25240
E 18-48hr 35°C Aerobic Growth; motility (-),
acid (-)

** Expected results when product is prepared with 1% glucose.

User Quality Control

** Expected results when product is prepared with 1% glucose.

Physical Appearance

CRITERION™ Cystine Tryptic Agar powder should appear homogeneous, free-flowing, and pink in color. The prepared media should appear clear, and red-pink in color.


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.

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