This
test is also known as the heat stable nuclease test. It is a 4hr test based on
the production of a heat stable DNase (thermonuclease) by Staphylococcus aureus.
It
is also used for determining and confirming the presence of S. aureus subsp aureus DNase from that produced by S. epidermidis or other micrococci. It is of particular use in
determining the presence of S. aureus
in positive blood culture bottles.
Unlike
other staphylococci, most strains of S.
aureus and Staphylococcus intermedius produce thermonuclease, a heat stable
DNase.
Subspecies
of Staphylococcus schleiferi are
DNase positive and produce heat stable nucleases. The thermonuclease test
detects the presence of this DNase.
The
organism is heated to destroy heat labile thermonucleases. It is then
inoculated on medium containing DNA and toluidine blue. The DNA is broken down
by heat stable nucleases resulting in the toluidine blue changing to red or
pink.
Posted by Tim Sandle
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