Liofilchem® Dey-Engley Neutralizing Broth, 500g

Dey-Engley Neutralizing Broth (D/E Broth) is a liquid culture medium specifically formulated for the neutralization of a wide range of antiseptics and disinfectants during microbiological testing. It is widely used in environmental sampling, disinfectant efficacy testing, and hygiene monitoring, enabling laboratories to differentiate between bacteriostatic and bactericidal activity.

By effectively neutralizing residual antimicrobial agents, D/E Broth ensures the accurate recovery and detection of viable microorganisms that may otherwise be inhibited by disinfectant carryover.

Intended Use

• Neutralization of disinfectants and antiseptics
• Environmental microbiological sampling
• Disinfectant efficacy and validation studies
• Differentiation between bacteriostatic and bactericidal effects
• Surface and equipment hygiene monitoring

Principle of the Medium

The formulation combines a nutrient-rich base with multiple chemical neutralizers, allowing microorganisms to recover and grow in the presence of disinfectant residues:

• Enzymatic digest of casein provides amino acids, nitrogen, carbon, minerals, and vitamins
• Yeast extract supplies B-group vitamins and growth factors
• Dextrose acts as a fermentable carbohydrate
• Neutralizing agents inactivate specific disinfectant classes
• Bromcresol purple serves as a pH indicator for microbial growth

Supplementation with Tween 80 (Polysorbate 80) enhances neutralization of phenolic disinfectants.

Disinfectants Neutralized

D/E Neutralizing Broth effectively neutralizes:

• Mercurial compounds → Sodium thioglycollate
• Iodine and chlorine → Sodium thiosulfate
• Aldehydes (formaldehyde, glutaraldehyde) → Sodium bisulfite
• Quaternary ammonium compounds → Lecithin
• Phenolic disinfectants → Tween 80 (supplement)

Typical Formula (g/L)

• Enzymatic Digest of Casein – 5.0
• Yeast Extract – 2.5
• Dextrose – 10.0
• Sodium Thioglycollate – 1.0
• Sodium Thiosulfate – 6.0
• Sodium Bisulfite – 2.5
• Lecithin – 7.0
• Bromcresol Purple – 0.02

Final pH: 7.6 ± 0.2 at 25 °C

Preparation

1. Suspend 34.0 g of powder in 1 L of deionized or distilled water
2. Add 5 mL of Tween 80 Supplement (ref. 80031)
3. Mix thoroughly
4. Sterilize by autoclaving at 121 °C for 15 minutes
5. Dispense into final containers

Test Procedure (Technique)

1. Add 1 mL of disinfectant to 9 mL of D/E Neutralizing Broth
2. Inoculate with an overnight microbial culture
3. Incubate at 35 ± 2 °C for 24–48 hours

To confirm viability:

• Subculture from broth onto D/E Neutralizing Agar (ref. 610086) or other suitable media
• Incubate plates at 35 ± 2 °C for 48 hours

Interpretation of Results

• Purple → Yellow color change → Microbial growth
• Pellicle formation → Microbial growth

Bacteriostatic effect:

• No growth in broth, but growth on subculture plates

Bactericidal effect:

• No growth in broth and no growth on plates

All positive broth tubes must show growth on plates.

Quality Control

Each batch undergoes:

1. Physical and label inspection
2. Microbiological performance testing

Test organisms (10³–10⁴ CFU, 24–48 h at 35 ± 2 °C):

• Bacillus subtilis ATCC® 6633 – Good growth
• Escherichia coli ATCC® 8739 – Good growth
• Pseudomonas aeruginosa ATCC® 27853 – Good growth
• Salmonella typhimurium ATCC® 14028 – Good growth
• Staphylococcus aureus ATCC® 6538 – Good growth

Product Specifications

Packaging

• Ref. 610088 – 500 g bottle 
  

Safety & Handling

• Not classified as hazardous under current legislation
• Consult Safety Data Sheet before use
• For professional use only by trained personnel

Waste Disposal

Dispose of unused medium and contaminated materials according to national and local regulations.

References

Dey & Engley (1970–1995) – foundational studies establishing D/E medium as a universal neutralizing system for antimicrobial chemicals in microbiological testing.

LIOFILCHEM® Dey-Engley Neutralizing Broth is a gold-standard neutralizing medium for disinfectant testing and environmental microbiology. Its broad-spectrum neutralization capacity, reliable growth recovery, and validated performance make it an essential tool for pharmaceutical, food, healthcare, and industrial hygiene laboratories.