Worksheet 11: Nitrate Reduction and Decarboxylase Test PDF

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Nitrate Reduction and Decarboxylase Test...

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Meet Patel

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Name: __________________________

Section Number: _____________

Worksheet 11: Nitrate Reduction and Decarboxylase Test 1.

Enter your conclusions for the Nitrate Reduction tests in the table below. Organism

Results Gas Bubble

Color of Broth

(Yes or No)

After Reagents A&B

After Zinc powder

E. coli

No&

Red&

----&

Alcaligenes faecalis

No&

Clear&

Pseudomonas aeruginosa

Yes&

----&

2.

Conclusion (Does the organism possess nitrate reductase?) Yes (+) No (-)

Yes (+) nitrate reductase positive No (-) nitrate reductase

Red/pink& negative Yes (+) nitrate reductase positive

----&

Wade, the not so observant research technician, made up a batch of nitrate broth but accidentally grabbed and used a bottle of potassium nitrite rather than potassium nitrate when preparing the media. Could you use this media to reliably determine whether an organism is nitrate reductase positive or not? Explain why or why not. [1.5 pts]

No, the media cannot be used to reliably determine whether an organism is nitrate reductase positive or not. Potassium nitrate is needed to correctly determine the nitrate reductase test results. The purpose of nitrate reductase test is to determine if the organism can convert nitrate to nitrite through reduction. If nitrite was used directly, we cannot tell if the organism can turn nitrate to nitrite, which gives us a false positive results.

3. Enter your conclusions below for the Decarboxylation tests in the table below. Does the organism possess the decarboxylase (positive (+) or negative (-))? The uninoculated tube for each condition is copper colored. Arginine Decarboxylase Broth Conclusion Positive or Negative (+/-)

Organism Color

E. aerogenes

yellow

P. stuartii

yellow

E. coli

purple

+

Lysine Decarboxylase Broth

Color

Conclusion Positive or Negative (+/-)

Ornithine Decarboxylase Broth

Color

Conclusion Positive or Negative (+/-)

purple

yellow

+ -

yellow

+ -

purple

+

purple

+

purple

4. Wade forgot to add a layer of sterile mineral oil on top of his arginine decarboxylase broth before incubating his tube. The next day, the tube remained copper in color. Wade concluded that the organism was arginine decarboxylase indeterminant. Is his answer reliable? What is the purpose of the sterile mineral oil and why is it important for decarboxylase production? [1.5 pts]

No, the answer is not reliable. Sterile mineral oil creates an anaerobic environment for the organism to grow in. Decarboxylase production happens in absence of oxygen which is under anaerobic condition. Without sterile mineral oil anaerobic environment is not created for organism to grow due to presence of oxygen (aerobic environment), thus it is not likely to produce enough acidic product to lower the pH that we need it to go....