2. Explain the functions of Solutions A and B. 3. If a culture did not undergo a color change on the addition of Solutions A and B, explain how you would interpret this result. 4. Explain why the development of a red color on the addition of zinc is a negative test. 5. Discuss the relationship between an organism's ability to reduce nitrate past the nitrite stage and that organism's proteolytic activity. 202 Experiment 28: Lab Report
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Solutions A and B are reagents used to test for nitrate reduction. A red color change indicates the presence of nitrite, an intermediate in nitrate reduction. Zinc is added as a confirmatory test. Show more…
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Nitrate reduction test can be used to differentiate between Pseudomonads and the Enterobacteriaceae. You inoculated your Nitrate broth with your unknown. After incubation, you added 5 drops of reagent A and 5 drops of reagent B. You observed a red color within 2 minutes. A. Is this a positive or negative reaction? B. Assuming you did not get a red color, you then added a pinch of Zinc powder to the tube. This time you did not get a red color. Is this a positive or a negative reaction? C. Explain your answers to questions A and B above. D. You streaked a starch plate with an organism. How would you know if the starch is hydrolyzed?
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You inoculated nitrate broth with an unknown and incubate at 37 degrees for 48 hrs. You are ready to test for nitrate reduction. After adding reagents A and B, the broth does not change color. Then you add zinc which causes the tube to turn a pinkish red color. Is this a positive or negative result for nitrate reduction? What does the zinc detect that helps you answer the previous question?
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Suppose you perform a nitrate reduction test on several organisms and obtain the following results: Sample Color after adding Nitrate reagents A and B Color after adding Zinc Gas bubble Negative control (uninoculated tube) beige red none E. coli Red N.D. (not done) none Pseudomonas aeruginosa N.D. N.D. bubble Enterococcus faecalis beige red none Bacillus cereus Beige beige none Use only the organisms-and the data- named in the table to answer the questions. 1. Name the organism(s) that does not reduce nitrate. 2. Name the organism(s) that produces nitrite. 3. Name the organism(s) that produces Nâ‚‚. 4. Name the organism(s) that is "positive" for nitrate reduction. 5. Why were reagents A and B not added to the tube containing Pseudomonas? 6. Why did the negative control tube turn red after adding zinc? 7. Why did we add a Durham tube to the nitrate broth?
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