DNase test

Microbiology

Principle

Deoxyribonuclease breaks down DNA in the agar. Hydrolysed areas become clear when acid is added, or show a colour change with methyl green or toluidine blue indicator.

Procedure

Spot-inoculate DNase agar and incubate overnight.
Flood with 1 M HCl (plain agar) or read the indicator colour change.

Results

Positive: clear zone around the growth (e.g. S. aureus, Serratia, Moraxella catarrhalis)
Negative: no clearing

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