|Show all biochemical tests|
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:
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