Dey-Engley Neutralizing Broth (DE Broth): Principle, Composition, Preparation, and Applications in Microbiology
Category: Microbiology Media | Tags: DE Broth, Neutralizing Broth, Pharmaceutical Microbiology, Disinfectant Testing
Introduction
Dey-Engley Neutralizing Broth (DE Broth) is a widely used neutralizing medium designed to inactivate antiseptics, disinfectants, and preservatives during microbial testing. It is commonly used in pharmaceutical, cosmetic, and food industries to recover microorganisms exposed to antimicrobial agents.
The medium was formulated by Dey and Engley in 1983 to provide efficient neutralization without toxic effects on microorganisms. It ensures accurate recovery and enumeration of microorganisms from disinfected surfaces, containers, or test samples.
Principle of Dey-Engley Neutralizing Broth
The principle of DE Broth lies in its ability to neutralize a wide range of disinfectants such as quaternary ammonium compounds, phenolics, iodine, chlorine, mercurials, aldehydes, and oxidizing agents.
Each chemical neutralizer present in the medium counteracts specific antimicrobial agents. For example:
- Lecithin neutralizes quaternary ammonium compounds.
- Polysorbate 80 neutralizes phenolics and hexachlorophene.
- Sodium thiosulfate neutralizes chlorine and iodine compounds.
- Sodium bisulfite neutralizes aldehydes.
- Sodium thioglycolate neutralizes mercurial compounds.
These agents together create a balanced environment that supports microbial recovery while eliminating residual antimicrobial action.
Composition of Dey-Engley Neutralizing Broth (per liter)
| Ingredients | Amount (g/L) |
|---|---|
| Casein Peptone | 5.0 |
| Lecithin | 7.0 |
| Polysorbate 80 | 5.0 |
| Sodium Thiosulfate | 6.0 |
| Sodium Bisulfite | 6.0 |
| Sodium Thioglycolate | 1.0 |
| Yeast Extract | 2.5 |
| Glucose | 1.0 |
| Agar (if solid medium required) | 15.0 |
| Distilled Water | 1000 mL |
| Final pH (at 25°C) | 7.6 ± 0.2 |
Preparation of Dey-Engley Neutralizing Broth
- Weigh and suspend 32.5 grams of DE Broth powder in 1000 mL of purified water.
- Mix thoroughly and heat gently to dissolve the medium completely.
- Distribute the medium into test tubes or bottles as required.
- Autoclave at 121°C for 15 minutes.
- After sterilization, cool the medium to room temperature and check for clarity.
If solid medium is required (for DE Agar), add agar before sterilization.
Quality Control (QC) of Dey-Engley Neutralizing Broth
To ensure performance, test DE Broth using the following ATCC reference strains:
- Staphylococcus aureus ATCC 6538
- Pseudomonas aeruginosa ATCC 9027
- Bacillus subtilis ATCC 6633
- Escherichia coli ATCC 8739
- Candida albicans ATCC 10231
The test organisms should show good growth and recovery even after exposure to disinfectants, confirming the neutralizing efficiency of the medium.
Applications of Dey-Engley Neutralizing Broth
- Used for neutralization and recovery of microorganisms exposed to disinfectants, antiseptics, or sanitizers.
- Employed in environmental monitoring and surface sampling in pharmaceutical industries.
- Used in validation of disinfectant efficacy tests (as per USP, EP, and ISO guidelines).
- Applied in sterility testing and microbial limit tests when antimicrobial residues are present.
- Ideal for testing disinfected water, surgical instruments, filling equipment, and cleanroom surfaces.
Storage and Shelf Life
Store DE Broth at 2–8°C in tightly closed containers, protected from light and moisture. The medium remains stable for up to 6 months if stored properly.
Conclusion
Dey-Engley Neutralizing Broth (DE Broth) plays a critical role in microbial recovery and neutralization testing, ensuring the reliability of disinfectant efficacy studies. Its balanced formula effectively neutralizes multiple classes of antimicrobial agents without harming microbial viability, making it a vital medium in pharmaceutical and industrial microbiology.
