Cat. no. C5520 CRITERION™ D/E Neutralizing Agar 113.4gm
Cat. no. C5521 CRITERION™ D/E Neutralizing Agar 500gm
Cat. no. C5522 CRITERION™ D/E Neutralizing Agar 2kg
Cat. no. C5523 CRITERION™ D/E Neutralizing Agar 10kg
Cat. no. C5524 CRITERION™ D/E Neutralizing Agar 50kg


Hardy Diagnostics CRITERION™ D/E Neutralizing Agar is used for the testing and neutralizing of antiseptics and disinfectants in order to detect organisms remaining after treatment. This agar is especially suited for environmental sampling where neutralization of the disinfectant is important to determine its bactericidal activity.

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.


CRITERION™ D/E Neutralizing Agar, which was developed by Dey-Engley, is capable of neutralizing a broad spectrum of antiseptic and disinfectant chemicals, including ethanol, quaternary ammonium compounds, phenolics, iodine, chlorine preparations, mercurials, formaldehyde and glutaraldehyde. It can determine the bactericidal capability of disinfectants and, therefore, is well suited for environmental sampling (swab and contact plate methods). D/E Neutralizing medium can neutralize higher concentrations of residual antiseptic and disinfectant chemicals than other neutralizing agents.

D/E Neutralizing Agar contains various neutralizing agents: lecithin, Tween®, sodium thiosulfate, sodium bisulfite, and sodium thioglycollate. Lecithin neutralizes quaternary ammonia compounds while phenolic disinfectants and hexachlorophene are neutralized by Tween®. Together, lecithin and Tween® neutralize ethanol. Sodium thiosulfate neutralizes iodine and chlorine, where as sodium bisulfite neutralizes formaldehyde and gluteraldehyde. Sodium thioglycollate neutralizes mercurials.

Complete neutralization of disinfectants is important because disinfectant carryover can cause a false no-growth test result. D/E Neutralizing medium effectively neutralizes the inhibitory effects of disinfectant carryover, allowing differentiation between bacteriostasis and the true bacterocidal action of disinfectant chemicals.

In addition to neutralizing agents, this medium contains ingredients that enhance the growth of a wide variety of microorganisms. Pancreatic digest of casein provides the carbon and nitrogen sources. Yeast extract provides vitamins and cofactors required for growth. Dextrose is added as a fermentable carbohydrate source. Bromcresol purple is added to the media as a colormetric indicator to demonstrate the production of acid from dextrose as a result of bacterial growth.


Gram weight per liter: 56.7gm/L
Dextrose 10.0gm
Lecithin 7.0gm
Sodium Thiosulfate 6.0gm
Pancreatic Digest of Casein 5.0gm
Tween® 80 5.0gm
Dipotassium Phosphate 3.3gm
Yeast Extract 2.5gm
Sodium Bisulfite 2.5gm
Sodium Thioglycollate 1.0gm
Monopotassium Phosphate 0.1gm
Bromcresol Purple 0.02gm
Agar 14.3gm

Final pH 7.6 +/- 0.2 at 25ºC.

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


Store the sealed bottle(s) containing dehydrated culture medium at 2-8ºC. 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 the color has changed from its original bluish-gray.

Store the prepared culture media at 2-8ºC.



1. Suspend 56.7gm of the dehydrated culture medium in one liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat to boiling to dissolve completely. Do not overheat.

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

4. Cool to 45-50ºC. and aseptically pour into Petri plates.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G224.



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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Bacillus subtilis
ATCC ® 6633
A 24-48hr 35°C Aerobic Growth; usually no color change
Escherichia coli
ATCC ® 25922
A 24-48hr 35°C Aerobic Growth; yellow color change
Pseudomonas aeruginosa
ATCC ® 9027
A 24-48hr 35°C Aerobic Growth; no color change
Salmonella enterica
ATCC ® 14028
A 24-48hr 35°C Aerobic Growth; yellow color change
Staphylococcus aureus
ATCC ® 6538
A 24-48hr 35°C Aerobic Growth; yellow color change

User Quality Control

Physical Appearance

CRITERION™ D/E Neutralizing Agar should appear moist, lumpy, and bluish-gray in color. The prepared medium should appear opaque, with an even suspension of particulates, and gray-purple to lavender 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.

6. American Public Health Association. Standard Methods for the Examination of Water and Wastewater, APHA, Washington, D.C.

7. Association of Official Analytical Chemists. Official Methods of Analysissm, AOAC, Washington, D.C.

8. The Official Compendia of Standards. 2008. USP27-NF22. United States Pharmacopeial Convention, Rockville, MD.

ATCC is a registered trademark of the American Type Culture Collection.
Tween is a registered trademark of ICI Americas, Inc.