Dey-Engley Neutralizing HiVeg™ Agar (D/E HiVeg™ Agar Disinfectant Testing)

Principle And Interpretation

Dey-Engley Neutralizing HiVeg™ Agar is prepared by using HiVeg™ hydrolysate in place of Casein enzymic hydrolysate which is free from BSE/TSE risks. Dey-Engley Neutralizing HiVeg™ Agar is modification of the medium formulated as per the procedure described by Engley and Dey (1). A strongly bacteriostatic substance inhibits the growth and reproduction of bacteria without killing them. These bacteria hold the ability to cause infection under favourable conditions. Dey-Engley Neutralizing Agar neutralizes a broad spectrum of antiseptics and disinfectants including quaternary ammonium compounds, phenolics, iodine and chlorine preparations, mercurials, formaldehyde and glutaraldehyde (1).

HiVeg™ hydrolysate provide source of nitrogen, carbon, long chain amino acids and other essential nutrients, dextrose acts as the energy source and yeast extract provides vitamin B-complex. The present formulation incorporates neutralizing substances for almost all the active substances that are used as antiseptics and disinfectants. Sodium bisulfite neutralizes aldehydes; sodium thioglycollate neutralizes mercurials; sodium thiosulfate neutralizes iodine and chlorine; lecithin neutralizes quaternary ammonium compounds; and polysorbate 80 neutralizes substituted phenolics (2-5). Bromocresol purple has been used as the indicator for dextrose utilization. Due to the high concentration of lecithin in the broth medium, turbidity cannot be used to detect growth. Therefore, bromocresol purple and dextrose are added to the medium that will detect dextrose fermenting organisms, if positive, will change the colour of the medium from purple to yellow(1).

For Agar Medium: Dey -Engley Neutralizing HiVeg™ Agar medium can be over-filled, producing a meniscus or dome-shaped surface that can be pressed onto a surface for sampling its microbial burden. Incubate the plates, by covering the lids, at an appropriate temperature. The presence of microorganism is determined by the appearance of colonies on the surface of agar medium. Neutralization Test: Growth in Neutralizing Broth and no growth in Neutralizing Broth Base indicate neutralization of disinfectant. To check bactericidal activity, both broth tubes are inoculated on D/E Neutralizing HiVeg™ Agar. Positive growth from negative tubes of Neutralizing Broth Base indicates bacteriostatic substance while negative growth indicates a bactericidal disinfectant. All positive tubes should show growth on Dey-Engley Neutralizing HiVeg™ Agar. The control disinfectants used in test procedure are 2% chlorine, 2%formaldehyde, 1% glutaraldehyde, 2% iodine, 2% phenol, 1/750 quaternary ammonium compounds, 1/1000 mercurials etc.