DNAse test | Agar | Principle | Interpretation

☰ Summary :

Ⅰ. Overview

Deoxyribonuclease (DNase) test is used to determine an organism's ability to hydrolyze DNA and use it as a source of carbon and energy for growth. Used mainly to differentiate Staphylococcus aureus from other Staphylococci.

DNases are enzymes that hydrolyze DNA and release free nucleotides and phosphate. DNases produced by bacteria are extracellular endonucleases that cleave DNA, producing a high concentration of oligonucleotides.

There are several media used to detect these enzymes, some do not use any indicator (requires the addition of HCl reagent) and others use various indicators (toluidine blue O or methyl green).

Ⅱ. Agar for DNase test / Principle

🏾 DNase agar without indicator

🏾 DNase agar with methyl green

🏾 DNase agar with toluidine blue O

Described by Schreier, originally designed to easily and quickly differentiate S. marcescens from other members of the KES division: Klebsiella, Enterobacter, Serratia.

Toluidine blue O ........................ 0,1 g

◈ Principle : When toluidine blue O (TBO) is added, a complex forms with the DNA, which changes structure when the DNA is hydrolyzed, resulting in a bright pink color.

Ⅲ. DNase Test Procedure / Results

  1. You will make a single line down the center of the box (if you are using 2 species of staphylococci, you can split the box in half and pass each organism down one side).
  2. Incubate at 30º C or 37º C.
  3. AFTER INCUBATION: If the DNase medium does not contain a color indicator: Flood the dish with 1N hydrochloric acid and Let the dish stand for a few minutes to allow the reagent to adsorb. Decant the excess hydrochloric acid, then examine the box within 5 minutes against a dark background.

🏿 DNase test positive :

  • 1. Serratia marcescens (Serratia fonticola is the only Serratia sp. that is DNase negative.)
  • 2. Staphylococcus aureus
  • 3. Campylobacter jejuni
  • 4. Moraxella catarrhalis
  • 5. Corynebacterium diphtheriae


  1. C D JEFFRIES- Rapid method for determining the activity of microorganisms on nucleic acids
  2. P. B. Smith - Improved Medium for Detecting Deoxyribonuclease-Producing Bacteria
  3. Schreier - Modification of Deoxyribonuclease Test Medium for Rapid Identification of Serratia marcescens
  4. TEXtBOOK Diagnostic Microbiology 4ed
  6. F.P. Pimenta - DNase test as a novel approach for the routine screening of Corynebacterium diphtheriae
  7. BD - DNase Test Agar
  8. BIOLOGY libretexts - Deoxyribonuclease (DNAse) Test
  9. T J Beveridge - Mechanism of gram variability in select bacteria
  10. CDC - DNase Test
  11. laboratoryinfo - Deoxyribonuclease (DNase) Test – Principle, Procedure, Uses, Result Interpretation