DNase Medium

DNase without Indicator is recommended for the detection of DNase activity of gram-negative and gram-positive bacteria, particularly Staphylococcus aureus, Branhamella (Moraxella) catarrhalis and Serratia marcescens. DNase with Toluidine Blue Agar is recommended for the detection of DNase in gram-negative bacteria, especially Serratia spp. Jeffries, Holtman, and Guse, reported the development of a medium that detects the deoxyribonuclease activity of microorganisms1. When plates of bacteria were flooded with 0.1N hydrochloric acid organisms possessing DNase activity degraded the DNA into nucleotide fractions resulting in a clear zone around the colonies. Whereas the organisms that do not pocess DNase activity, HCl combines with nucleate salts to yield free nucleic acid producing an opaque appearance in the medium.

DNase with Toluidine Blue O, developed by Schreier in 1969, is a modification of the formula developed by Jeffries, Holtman, and Guse1,2. DNA is incorporated into the medium to detect organisms which possess the DNase. Toluidine blue O serves as the color indicator and it eliminates the need to add HCl to the plate. The complexing of toluidine blue O with DNA produces a blue color in the uninoculated medium. Organisms which depolymerize DNA result in the formation of a dye, oligonucleotide, and mononucleotide complex. Metachromatic properties of the indicator thereby produce a visible bright rose-pink color in the surrounding area of the organisms possessing the DNase enzyme. Because toluidine blue may be inhibitory to some gram-positive organisms, it is recommended for the detection of DNase in gram-negative microorganisms.


Product NameCatalog #Quantity
DNase Agar mono plate, 90 x 15 mm CD9310P 10/pk
DNase Slant CD9310S 10/pk
DNase Broth CD9310B 10/pk


Quality Control



The following organisms are routinely used for testing for this medium.
Test OrganismsResults
Without Toluidine Blue O  
  1. Serratia marcescens ATCC® 13880
Growth; clear zone around growth after addition of HCl
  1. Branhamella (Moraxella) catarrhalis ATCC® 25240
Growth; clear zone around growth after addition of HCl
  1. Staphylococcus aureus ATCC® 25923
Growth; clear zone around growth after addition of HCl
  1. Staphylococcus epidermidis ATCC® 12228
Growth; no clear zones, entire plate turns opaque white after addition of HCl
  1. Escherichia coli ATCC® 25922
Growth; no clear zones; entire plate turns opaque white after addition of HCl
With Toluidine Blue O  
  1. Serratia marcescens ATCC® 13880
Growth; pink zone around colonies, must use transmitted light to read, may take up to 48 hours for color change
  1. Branhamella (Moraxella) catarrhalis® 25240
Growth; pink zone around colonies, must use transmitted light to read, may take up to 48 hours for color change
  1. Staphylococcus aureus ATCC® 25923
Growth; pink zone around colonies, must use transmitted light to read, may take up to 48 hours for color change
  1. Escherichia coli ATCC® 25922
Growth; no color change
  1. Staphylococcus epidermidis ATCC® 12228
Growth; no color change


User Quality Control



Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 7.3 +/- 0.2 at 25°C)
Pancreatic Digest of Casein 15.0
Papaic Digest of Soybean Meal 5.0
Sodium Chloride 5.0
Deoxyribonucleic Acid 2.0
Agar 15.0
DNase with Toluidine Blue contains the above ingredients with the addition of:  
Toluidine Blue O 0.075
2 total citations

  1. Jeffries, Holtman and Guse. 1957. J. Bacteriol.; 73:590
  2. Schreier, J.B. 1969. Am. J. Clin. Pathol.; 51:711-716.
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