DNase Test HiVeg™ Agar Base w/o DNA

Principle and Interpretation

This medium is prepared by using HiVeg hydrolysate which is free from BSE/TSE risks. DNase Test HiVeg Agar Base is the modification of DNase Test agar base which is used for detecting deoxyribonuclease activity of bacteria and fungi and particularly for identification of pathogenic Staphylococci. DNase activity was observed by Weckman and Catlin (1) in Micrococci and found the correlation with coagulase activity as coagulase positive species were DNase positive. Di Salvo (2) confirmed the results of Weckman and Catlin and observed accurate correlation of DNase and coagulase activity. In his experiment Di Salvo incorporated DNA and calcium chloride to activate DNase enzyme. DNase medium was modified by adding toluidine blue by Schreier. DNase Test HiVeg Agar Base w/o DNA is modified by adding bromothymol blue instead of toluidine blue (3). This modified medium achieved faster identification of Serratia marcescens and could differentiate Serratia from other members of the Enterobacteriaceae. HiVeg hydrolysate and papaic digest of soyabean meal provide essential nutrients. DNase depolymerizes the DNA resulting in the formation of a clear zone around the microbial growth which is visualized by flooding the plate with hydrochloric acid (4). When bromothymol blue is added to the medium itself, DNase activity results in the production of a colourless to yellow reaction. Further confirmatory tests for identification should be carried out.