Sunday, 17 May 2015

Thermonuclease Test explained

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.

In relation to the thermonuclease test, Public Health England has issued a technical report, including safety information. The report can be accessed here.

Posted by Tim Sandle