Cat. no. K105 Neutralizing Buffer, 16x125mm Tube, 10ml 20 tubes/box


Hardy Diagnostics Neutralizing Buffer is used in environmental monitoring procedures for the sterility testing of equipment and surfaces.

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


Neutralizing Buffer is used for the sampling of equipment and surfaces because it has the ability to neutralize the bactericidal and bacteriostatic effects of quaternary ammonium compounds. Standard Methods for the Examination of Dairy Products contains a procedure for the sterility testing of equipment.(3) Compendium of Methods for the Microbiological Examination of Foods details a procedure for the sterility testing of surfaces and utensils.(1)

Neutralizing Buffer contains potassium phosphate to maintain the pH. Sodium thiosulfate and aryl sulfonate complex act to neutralize chlorine and quaternary ammonium compounds. Neutralizing Buffer is not toxic to microorganisms, even when used in procedures that call for concentrations up to 10 times the single strength buffer.


Ingredients per liter of deionized water:*

Aryl Sulfonate Complex 5.0gm
Sodium Thiosulfate 160.0mg
Potassium Phosphate 42.5mg
Sodium Hydroxide 8.0mg

Final pH 7.2 +/- 0.3 at 25°C

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


Storage: Upon receipt store at 2-30°C away from direct light. Media should not be used if there are any signs of contamination, deterioration, discoloration, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.



Sample Collection(1)

Aseptically collect sample. Collect sample by rubbing the swab over the sample area (approximately 50cm2), reversing directions between strokes. Repeat the collection procedure three more times, returning the swab head to the Neutralizing Buffer after swabbing each area. When sampling utensils such as knives or ladles, run the swab over the entire surface of the instrument three times, as described above. If sample is not immediately taken to the lab the sample can be refrigerated for up to 24 hours prior to analysis.


Prior to plating, shake the tube vigorously (50 cycles of 15cm in 10 seconds). Prepare pour plates, using Standard Methods Agar or other appropriate media, plating 1.0ml and 0.1ml samples of Neutralizing Buffer containing the sample. Incubate plates at 35°C for 48 hours, then calculate the number of colonies from 50cm2 sample area.(2)

Refer to listed references for more information on procedures involving Neutralizing Buffer.(1,2,4)


Generally, the U.S. Public Health Service states that cleaned and sterilized food service equipment should not have more than 100 colonies per utensil or surface area sampled.(1) More often, the type of organism, rather than numbers is more critical in an HACCP system. It could be that more stringent specifications need to be made based on the type of surface sampled and the nature of the finished product that is being produced.



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.


Neutralizing Buffer is routinely tested at Hardy Diagnostics using the following procedure:

Dilute a disinfectant containing a quaternary ammonium compound such as Roccal with Neutralizing Buffer from 1:2,500 to 1:100,000. Inoculate the tubes with Staphylococcus aureus ATCC® 6538. Prepare pour plates by transferring 1.0ml from each dilution to Standard Methods Agar. Incubate the plates for 40-48 hours at 35°C. Record growth. Neutralizing Buffer inactivates the bactericidal activity which the growth pattern should reflect.

Test Organisms Incubation Results
Time Temperature Atmosphere
Staphylococcus aureus
ATCC ® 6538
24-48hr 35°C Aerobic Recovered

User Quality Control


Neutralizing Buffer should appear clear and colorless to light amber.


1. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods, APHA, Washington, D.C.

2. Tiedman, W.D., Chairman. 1948. Technique for the Bacteriological Examination of Food Utensils. Committee Report. American Journal of Public Health Yearbook.

3. American Public Health Association. Standard Methods for the Examination of Dairy Products, APHA, Washington, D.C.

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