Cat. no. C6940 CRITERION™ SIM Medium 60gm
Cat. no. C6941 CRITERION™ SIM Medium 500gm
Cat. no. C6942 CRITERION™ SIM Medium 2kg
Cat. no. C6943 CRITERION™ SIM Medium 10kg
Cat. no. C6944 CRITERION™ SIM Medium 50kg


Hardy Diagnostics CRITERION™ SIM Medium is recommended for the differentiation of gram-negative enteric bacilli, such as Salmonella and Shigella, on the basis of sulfide production, indole formation, and motility.

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.


The formulation of SIM Medium is designed to allow the detection of sulfide production, indole formation and motility.

The medium contains ferrous ammonium sulfate and sodium thiosulfate, which together serve as indicators for the production of hydrogen sulfide. Hydrogen sulfide production is detected when ferrous sulfide, a black precipitate, is produced as a result of ferrous ammonium sulfate reacting with H2S gas.

Casein peptone, another component of SIM Medium, is rich in tryptophan. Organisms possessing the enzyme tryptophanase degrade tryptophan to indole. Indole is detected upon the addition of Kovacs Indole Reagent (Cat. no. Z67) following incubation of the inoculated medium. Indole combines with p-dimethylaminobenzaldehyde and produces a red band at the top of the medium. A negative indole test produces no color change upon the addition of Kovacs Indole Reagent.

The small amount of agar added to the medium provides a semi-solid structure allowing for the detection of bacterial motility. 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.

SIM Medium also contains animal tissue which provides amino acids and nutrients necessary for bacterial growth.


Gram weight per liter: 30.0gm/L
Pancreatic Digest of Casein 20.0gm
Peptic Digest of Animal Tissue 6.1gm
Ferrous Ammonium Sulfate 0.2gm
Sodium Thiosulfate 0.2gm
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 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 beige.

Store the prepared culture media at 2-30ºC.



1. Suspend 30.0gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely.

3. Dispense medium into tubes to an approximate depth of 3 inches.

4. Sterilize in the autoclave at 121ºC. for 15 minutes.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. Q30.


The inoculum should be taken from a solid medium. Use of an inoculum from a liquid or broth suspension will delay the initiation of growth and may result in erroneous results.

When inoculating semi-solid media, it is important that the inoculating needle be removed along the exact same line used to inoculate the medium. A fanning motion may result in growth along the stab line that may result in false-positive interpretation.

Motility and H2S results must be interpreted prior to addition of Indole Kovacs Reagent.

Weak motile organisms or organisms that possess damaged flagella (due to heating, shaking, or other trauma) often result in false-negative motility tests. Motility results may be confirmed by performing a hanging drop motility test. Consult listed references for procedure.(2-4,6)

Some microorganisms, such as Yersinia enterocolitica, demonstrate motility best at 25ºC.

Organisms that require oxygen for growth, such as Pseudomonas aeruginosa, will produce a spreading film on the surface of the medium and will not extend from the line of inoculation where oxygen is depleted.

Erroneous results may occur if caps are not loose during incubation.


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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Salmonella enterica
ATCC ® 14028
D 18-24hr 35°C Aerobic Growth; motility positive, H 2 S positive (black color along stab line), indole negative
Escherichia coli
ATCC ® 25922
D 18-24hr 35°C Aerobic Growth; motility positive, H2S negative, indole positive (Kovacs Reagent turns pink after adding three drops)

User Quality Control


CRITERION™ SIM Medium powder should appear homogeneous, free-flowing, and beige in color. The prepared media should appear as a semi-solid medium, slightly opalescent, and medium amber 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.