Cat. no. P130 D/E Neutralizing Agar, Irradiated,Contact Plate, TapTight™, Triple Bagged, 14.5ml 10 plates/bag
Cat. no. P99 D/E Neutralizing Agar, Contact Plate, 14.5ml 10 plates/bag
Cat. no. G224 D/E Neutralizing Agar, 15x100mm plate, 18ml 10 plates/bag
Cat. no. U113 D/E Neutralizing Agar, 16oz bottle, 300ml 12 bottles/box
Cat. no. U168 D/E Neutralizing Agar, 16oz bottle, 400ml 12 bottles/box


Hardy Diagnostics D/E Neutralizing Agar is used for the testing efficacy and neutralizing of antiseptics and disinfectants based on neutralizing the chemical and detecting organisms remaining after treatment.

This product is not intended to be used for the diagnosis of human disease.


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 media 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 media effectively neutralizes the inhibitory effects of disinfectant carryover, allowing differentiation between bacteriostasis and the true bacteroidal action of disinfectant chemicals.

In addition to neutralizing agents, this media 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 growth factors 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.


Ingredients per liter of deionized water:*

Dextrose 10.0gm
Lecithin 7.0gm
Sodium Thiosulfate 6.0gm
Pancreatic Digest of Casein 5.0gm
Tween®80 5.0gm
Yeast Extract 2.5gm
Sodium Bisulfite 2.5gm
Sodium Thioglycollate 1.0gm
Monopotassium Phosphate 0.1gm
Bromcresol Purple 0.02gm
Agar 13.5gm

Final pH 7.6 +/- 0.3 at 25°C

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


Storage: Upon receipt store at 2-8°C 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. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.



Before Use of Plates: It is possible that variation in temperature and pressure during shipping and storage may cause condensation on the innermost bag surrounding the product. If condensation of the packaging or plates is observed, remove the plates from the innermost packaging in a sterile environment and allow them to dry for 10-15 minutes before use.

For re-melting bottled media: Liquefy the medium by autoclaving at 121°C for 1-3 minutes Cool the medium to 45-50°C and pour into sterile petri dishes. Allow the agar to solidify for at least 30 minutes prior to use. Alternatively, a covered, boiling waterbath (100°C) can be used. There should be enough water in the waterbath to reach the top of the media line. Heat in a waterbath until melted through. A covered waterbath will help to reach and maintain the media temperature prior to dispensing. Note: After autoclaving, do not heat media using a hot plate, heat block or waterbath for longer than 3 hours at 45-50°C. Melt only enough media that can be poured within a 3 hour time period. For optimal performance, sterile solidified medium should be remelted only once prior to use.

Contact Plate Method: Allow plates to warm to room temperature, and agar surface to dry. Select a surface to test. Sample the surface by firmly pressing the agar against the test area, using the thumb and second finger to hold the plate, and the first finger to press firmly and evenly on the base. The same amount of pressure should be used for each sample. Do not move the plate laterally, as this spreads contaminants across the agar surface. A rolling motion may be used when slightly curved surfaces are sampled. Areas to be assayed may by divided into grids or sections, and days, as required. Observe for growth and/or a zone of color change from purple to yellow which occurs when the dextrose is fermented.


Colonies of dextrose fermenting microorganisms will be surrounded by a yellow zone.

Consult listed references for information pertaining to colony morphology and biochemical tests required for identification.(1-3,5,6)



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
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



D/E Neutralizing Agar should appear opaque, with an even suspension of particulates, and lavender in color.

E. coli growing on D/E Neutralizing Agar

Uninoculated plate of D/E Neutralizing Agar (Cat. no. P99).


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

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

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

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

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

7. Centers for Medicare & Medicaid Services (CMS). Individualized Quality Control Plan (IQCP)

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