Thermonuclease Agar

Presumptively identify Staphylococcus aureus with Thermo Scientific™ Remel Thermonuclease Agar (w/toluidine blue). Zarzour and Belle reported the usefulness of the thermonuclease test in confirming questionable coagulase-negative S. aureus isolates¹. Shanholtzer and Peterson compared the thermonuclease test with the tube coagulase and clumping factor² and found that thermonuclease test to be as reliable as the tube coagulase and less time consuming to perform. Madison and Baselski demonstrated 100% correlation with the subsequent identification of the isolate as S. aureus by the coagulase test.

Thermonuclease Agar w/ Toluidine Blue is a solid medium recommended for use in qualitative procedures for presumptive identification of S. aureus. The nuclease produced by S. aureus is thermostable, whereas that produced by other organisms is thermolabile^3-5. Ratner and Stratton confirmed that the thermonuclease test could be performed directly from a blood culture broth showing gram-positive cocci in clusters on a Gram strain, thus allowing a same-day report of presumptive for S. aureus⁶. The thermonuclease enzyme produced by S. aureus depolymerizes DNA in the area adjacent to the well after incubation of the plate for 2-4 hours. The metachromatic property of toluidine blue produces a pink zone of diffusion or halo around the well.

Broth cultures incubated for 2 hours followed by boiling for 15 minutes are tested in wells cut into the agar plate.

• Ready-to-use – Convenience of prepared medium
• Easy to interpret – Pink zone of clearing at the edge of the well with a darker blue ring at the outer periphery of the zone indicates positive test whereas no zone or a small clear zone (without pink) and no hyper-pigmented peripheral ring indicates negative test

The medium consists of sodium chloride, calcium chloride, tris base, deoxyribonucleic acid, toluidine blue, and agar.

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Remel™ and Oxoid™ products are now part of the Thermo Scientific brand.