Dey-Engley Neutralizing Broth ISO

Peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Dextrose is the fermentable carbohydrate providing carbon and energy. Five neutralizers inactivate a number of disinfectant and antiseptic chemicals. Sodium bisulfite neutralizes aldehydes. Sodium thioglycollate neutralizes mercurials. Sodium thiosulfate neutralizes iodine and chlorine. Lecithin neutralizes quaternary ammonium compounds. Polysorbate 80, a non-ionic surface active agent, neutralizes substituted phenolics. Bromocresol purple is used as an indicator for dextrose utilization. The organisms that ferment dextrose will turn the medium from a purple to yellow color.

Those organisms that ferment dextrose will turn the medium from purple to yellow. The growth of Pseudomonas species, which do not ferment dextrose, can be detected by the formation of a pellicle on the surface of the broth.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 39 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Distribute into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Instructions for use

For the neutralization and testing of antiseptics and disinfectants:

1. Add 1 mL of the test sample to one tube containing 9 mL of Neutralizing Broth.
2. Add an amount of inoculum from a broth culture as desired.
3. Incubate tubes at 35 °C.
4. Growth is indicated by a color change from purple to yellow or by pellicle formation.
5. Growth in the Neutralizing Broth indicates the neutralization of the disinfectant.

For the detection of microorganisms on surfaces of sanitary interest:

1. Apply a sterile cotton swab on the material surface to recover the microorganisms.
2. Immerse the swab in the Neutralizing Broth tube.
3. Incubate tubes at 35 °C.
4. Growth is indicated by a color change from purple to yellow or by pellicle formation.

Due to the composition of the Dey-Engley Neutralizing Broth and its hygroscopic properties, the powder could appear lumpy and moist. This phenomenon does not affect the microbiological performance of the medium.

• Downes and Ito (ed.). 2001. Compendium of methods for the microbiological examination of foods, 4th ed. American Public Health Association, Washington, D.C.
• Association for the Advancement of Medical Instrumentation. 1984. Process control guidelines for gamma radiation sterilization of medical devices. AAMI, Arlington, VA.