Clinical laboratory evaluation of the thermonuclease test

Simultaneous testing for clumping factor, coagulase, deoxyribonuclease, and thermonuclease was performed on 189 clinical isolates of gram-positive cocci with strong catalase activity to determine the suitability of the thermonuclease test as a routine procedure for the identification of Staphylococcus aureus. Positive reactions to all four tests were exhibited by 72 of the strains while 88 of the isolates gave uniformly negative results. Although discrepancies were found between the reactions of 29 organisms, differences were found between the reactions of 29 organisms, differences between tube coagulase ant thermonuclease results were rare. Greater than 90% of positive reactions for both tube coagulase and thermonuclease tests were detected within a four-hour incubation period. The thermonuclease test was found to be simple, reliable, inexpensive and rapid. This test gave easily interpretable reactions within an eight-hour workday, even when only one or two isolated colonies were used for testing. The thermonuclease test is well suited for use as a primary clinical laboratory procedure for the identification of Staphylococcus aureus.