D/E Neutralising Agar (Dey & Engley)

Product information

Description:

D/E Neutralising Agar is used to neutralise and determine the bactericidal activity of antiseptics and disinfectants. Developed by Dey and Engley, this agar neutralises a broad spectrum of antimicrobial chemicals, producing better results than those obtained using alternatives such as Letheen Agar. Complete neutralisation is required to prevent false results arising from disinfectant carryover. D/E Neutralising Agar is used as the plating medium when testing disinfectants using D/E Neutralising Broth and D/E Neutralising Broth Base. It can also be used to test disinfectants by a disc diffusion method. D/E Neutralising Agar contains thioglycollate to neutralise mercurial compounds, sodium thiosulphate to neutralise iodine and chlorine and sodium bisulphite to neutralise formaldehyde and gluteraldehyde. Lecithin is included to neutralise quaternary ammonium compounds and Tween® 80 neutralises phenols, hexachlorophene, formalin, and combined with lecithin, ethanol. Bromocresol purple allows detection of growth via a colour change from purple to yellow when organisms ferment the glucose contained in the medium.

Formula g/litre
Glucose 10.0
Lecithin 7.0
Sodium thiosulphate 6.0
Tween®80 5.0
Tryptone 5.0
Sodium bisulphite 2.5
Yeast extract 2.5
Sodium thioglycollate 1.0
Bromocresol purple 0.02
Agar 15.0

Method for reconstitution
Weigh 54.0 grams of powder and disperse in 1 litre of deionised water. Allow to soak for 10 minutes. Sterilise by autoclaving at 121°C for
15 minutes. Cool to 47°C and pour into sterile Petri dishes and allow to set.

Appearance: Purple opaque gel.

pH: 7.6 ± 0.2

Minimum Q.C. organisms:
Bacillus subtilis NCIMB 8054
Escherichia coli NCIMB 12210
Pseudomonas aeruginosa NCIMB 12469
Salmonella typhimurium NCIMB 13284
Staphylococcus aureus NCIMB 12702

Storage of Powder: Store at 2-8°C in the dark. Formulation is very hygroscopic, keep container tightly closed after use.
Storage of Prepared Medium: Plates – up to 7 days at 2-8°C in the dark.

Inoculation: Consult appropriate references as this product is used in several procedures.

Incubation: 37°C aerobically for 24-48 hours.

Interpretation: Count all colonies for total counts, count yellow colonies for differential acid producer count.
Non-acid producing colonies are grey to colourless.