Kingella denitrificans can be differentiated from Neisseria gonorrhoeae because it is able to

• A. Able to grow on Thayer-Martin agar
• B. Able to reduce nitrates
• C. Oxidase positive
• D. Glucose positive

Answer: (B)

The key idea is using a biochemical test to distinguish closely related Gram-negative bacteria. Kingella denitrificans can reduce nitrates to nitrites (or further to nitrogen), and this activity is detected by the nitrate reduction test. When you run the test, a positive result—typically a red color after adding reagents that detect nitrite—indicates nitrate reduction. Neisseria gonorrhoeae, under the same test conditions, generally does not reduce nitrate, so it does not produce that nitrite signal. This difference makes nitrate reduction the best way to tell these two apart. Other traits like specific selective-medium growth or general oxidase status aren’t as reliable for differentiating these two organisms, so the nitrate reduction capability provides a clearer diagnostic distinction.