DNase Test HiVeg™ Agar Base

Principle and Interpretation

DNase Test HiVeg Agar Base is specially developed from HiVeg hydrolysate to avoid BSE/TSE risks associated with animal origin casein enzymic hydrolysate. DNase Test HiVeg Agar is the modification of DNase Test Agar which is used for detecting deoxyribonuclease activity of bacteria and fungi and particularly for identification of pathogenic Staphylococci. With added toluidine blue, it is used in differentiation and identification of nonpigmented Serratia species isolated from clinical sources that might be improperly identified as Enterobacter and Klebsiella species. 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. DiSalvo (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 (3). Modified medium achieved faster identification of Serratia marcescens and could differentiate Serratia from other members of the Enterobacteriaceae.

HiVeg hydrolysate, papaic digest of soyabean meal provide essential nutrients. The DNase depolymerizes the DNA resulting in the formation of a clear zone around the microbial growth which is visualized by flooding the plate with 1N hydrochloric acid (4). When toluidine blue is added to the medium itself then, DNase activity results in the production of a bright pink zones surrounding growth due to the metachromatic property of toluidine blue. Some strains of Staphylococci may be inhibited on DNase Test Agar due to toluidine blue. Further confirmatory tests for the identification should be carried out.