Question

Thermonuclease test is used for detection of

• A. Escherichia coli
• B. Salmonella spp.
• C. Enterococci spp.
• D. Staphylococci spp.

Hint:

The thermonuclease test serves as an indirect indicator of staphylococcal enterotoxins, as both the enzyme and the toxins are heat-stable and survive pasteurization.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Rapid screening tests are essential in dairy quality control to detect the historical growth of toxigenic pathogens.
The thermonuclease (TNase) assay is used as an index test to evaluate the safety of milk and milk products.

Step 2: Detailed Explanation:
Pathogenic strains of the genus Staphylococcus (most notably Staphylococcus aureus) secrete an extracellular nuclease.
This enzyme, known as thermonuclease (TNase), is exceptionally heat-stable and can withstand boiling for 30 minutes or standard pasteurization.
Because TNase is highly heat-stable, it remains active in dairy products even after pasteurization has killed the vegetative cells.
The production of thermonuclease correlates closely with the production of staphylococcal enterotoxins.
Therefore, detecting active thermonuclease indicates that staphylococci have grown in the milk and may have produced enterotoxins.
This makes the TNase test a rapid, cost-effective screening method that is faster than directly testing for enterotoxins.
In contrast:
Escherichia coli does not produce a highly heat-stable extracellular nuclease of diagnostic utility.
Salmonella species are detected using selective enrichment and serological or molecular assays.
Enterococci species are primarily monitored using bile esculin azide agar and are not characterized by diagnostic thermonuclease production.

Step 3: Final Answer:
Consequently, the thermonuclease test is specifically used for the detection of Staphylococci spp.