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DNase test


Many bacteria have enzymes that break down nucleic acids. The bacteria can then use the resulting nucleotides to build up their own nucleic acids. DNase is such an enzyme, which thus hydrolyzes DNA. Existence of DNase is characteristic for certain species or strains of bacteria and can be used for typing.



Figure: DNase test of Staphylococcus spp. The strain in the upper streak is negative (no clearing around the streak), whereas the strain in the lower streak is positive. (Image: SLU/SVA)

Presence of DNase can be determined by cultivation on an agar plate, which contains DNA. If the bacterium has DNase and if the bacteria are allowed to grow over night, the DNA will be hydrolyzed into the constituting nucleotides. Diluted hydrochloric acid (HCl) is then poured onto the plate and there will be a clear zone close to the colonies or the streak, because individual nucleotides are soluble in diluted HCl, but not DNA, which precipitates in the rest of the plate.


The test is useful to distinguish between:

  • Serratia spp. and Enterobacter spp.
  • Staphylococcus aureus (most strains are coagulase positive) and coagulase negative Staphylococcus spp.
  • Moraxella catarrhalis and Neisseria spp.


Updated: 2017-12-08.


Phage therapy for treatment of American foulbrood caused by Paenibacillus larvae infections in honey bees
Wild bee on a black chokeberry flower.

It has recently been shown that phage therapy can be used to treat and cure hives of honey bees, which are suffering from American foulbrood. Read more about this here or on our blog.

Published 2018-05-17. Read more...

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Swedish University of Agricultural Sciences