ID#: 16225
Caption:
This Petri dish culture plate contained a growth medium that had been colored blue due to the addition of toluidine blue dye. The medium was subsequently inoculated with an Enterobacter sakazakii bacterial culture at 1-day intervals, being allowed to incubate for a 1-day (bottom), 2-day (middle), and a 3-day (top) time period, at a temperature of 36°C. The resultant DNase reaction revealed positive results after a 2, and 3-day incubation period, evidenced by the light-pink halo surrounding the punctate-, hyphenated-, and X-shaped colonies. The DNase test measures the production of the extracellular enzyme, deoxyribonuclease (DNase), a chemical break down DNA. In a positive DNase test, the DNA is fragmented, freeing the double-stranded DNA (dsDNA) from its bonds with the dye contained in the medium, in this case toluidine, and leaving behind a lightly colored, pinkish tinted halo around the colonies.
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Content Provider(s): CDC/ Dr. J.J. Farmer
Creation Date: 1978
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