Used in microbiology to detect deoxyribonuclease (DNase) activity in bacteria. The agar contains DNA and toluidine blue indicator. After incubation, the plate is flooded with 1N hydrochloric acid (HCl). When an organism produces DNase enzyme, it hydrolyzes the DNA in the medium, preventing the formation of a blue DNA-toluidine blue precipitate upon acidification, resulting in a clear zone around bacterial growth. Unhydrolyzed DNA areas form a blue precipitate, providing contrast for easy visualization of positive results. Commonly used to differentiate pathogenic strains such as Staphylococcus aureus, which typically produces DNase, from other less pathogenic staphylococci. Also helpful in identifying certain Streptococcus and Serratia species based on their DNase production. The test is simple, rapid, and effective for use in clinical and research laboratories.