Cat. no. G129 MacConkey Agar with Sorbitol, Cefixime, and Tellurite,
15x100mm Plate, 18ml
10 plates/bag


Hardy Diagnostics MacConkey Agar with Sorbitol, Cefixime, and Tellurite (CT-SMAC) is used for the selective and differential isolation of enterohemorrhagic Escherichia coli O157.


E. coli serogroup O157 is a group of enteric pathogens that cause hemorrhagic colitis and hemolytic uremic syndrome. MacConkey Agar with Sorbitol was developed as a medium capable of differentiating E. coli O157 from non-O157 E. coli on the basis of sorbitol fermentation. (1)

MacConkey Agar with Sorbitol, Cefixime, and Tellurite inhibits the growth of most non-verocytotoxigenic E. coli strains and most other non-sorbitol fermenting species. A number of organisms which may be mistaken for E. coli O157 on traditional MacConkey Agar with Sorbitol are inhibited on MacConkey Agar with Sorbitol, Cefixime, and Tellurite. (1)


Ingredients per liter of deionized water:*

Pancreatic Digest of Gelatin 17.0gm
Sorbitol 10.0gm
Sodium Chloride 5.0gm
Proteose Peptone 3.0gm
Bile Salts Mixture 1.5gm
Neutral Red 30.0mg
Potassium Tellurite 2.5mg
Crystal Violet 1.0mg
Cefixime 0.05mg
Agar 13.5gm

Final pH 7.1 +/- 0.3 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), contamination, or if the expiration date has passed.



Specimen Collection: Consult appropriate references to determine how to correctly collect the specimen to be tested (stool, food, etc.). (2-4)

Method of Use: Allow plates to warm to room temperature. The agar surface should be dry before inoculating. Inoculate plates with a loopful of sample and streak using the four quadrant method to obtain isolated colonies. Incubate plates aerobically at 37ºC. for 24 hours. Examine media macroscopically for typical colonies.


E. coli O157, which does not ferment Sorbitol, will grow as colorless colonies on CT-SMAC. Any colony capable of fermenting sorbitol will appear as pink colonies on CT-SMAC.


Reading CT-SMAC beyond 24 hours should be avoided. The pink color produced by sorbitol fermenting colonies will fade after time. In addition, colonies inhibited by the tellurite and cefixime in the media may begin to overwhelm the medium after 24 hours.

A heavy inoculum should be avoided, as it can exhaust the sorbitol, giving a false-negative sorbitol fermentation reaction.

Streaking for isolation is critical as sorbitol negative colonies present in low numbers may be buried beneath sorbitol positive colonies and difficult to distinguish.

The CT-SMAC Agar can be used to aid in the identification of bacteria. Additional biochemical and serological testing is recommended for complete identification.

Sorbitol-negative colonies may be presumptively identified as E. coli O157 using our E. coliPRO™ O157 Kit (Cat. no. PL070HD). Further serotyping with H7 antiserum is necessary for definitive identification (Cat. no. 221591).


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
Escherichia coli O157:H7
ATCC ® 43888**
A 24hr 35°C Aerobic Clear colonies seen; no fermentation of sorbitol
Escherichia coli
ATCC ® 25922**
B 24hr 35°C Aerobic Partial to complete inhibition; pink colonies seen; fermentation of sorbitol
Proteus mirabilis
ATCC ® 12453
B 24hr 35°C Aerobic Partial to complete inhibition
Enterococcus faecalis
ATCC ® 29212
B 24hr 35°C Aerobic Partial to complete inhibition

** Recommended QC strains for User Quality Control according to the CLSI document M22 when applicable.

User Quality Control


CT-SMAC Agar should appear slightly opalescent, and reddish-purple in color.

E. coli O157 growing on CT-SMAC Agar

Escherichia coli O157:H7 (ATCC ® 43888) colonies growing on CT-SMAC Agar (Cat. no. G129). Incubated aerobically for 24 hours at 35ºC.

P. mirabilis on CT-SMAC Agar

Uninoculated plate of CT-SMAC Agar (Cat. no. G129).


1. Zadik, P.M., P.A. Chapman and C.A. Siddons. 1993. J. Med. Microbiol.; 39:155-158.

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. U.S. Food and Drug Administration. Bacteriological Analytical Manual. AOAC, Arlington, VA. .

5. Chapman, P.A., et al. 1991. J. Med. Microbiol.; 35:107-110.

6. Quality Assurance for Commercially Prepared Microbiological Culture Media, M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

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