Microbiology Biology 250

Microbiology Biology 250 Stavney Name Lab Quiz III

25 points total. Use Scantron answer form for questions 1-20, and write in the answer directly onto page 4 for Question 20.

1. The oxidase test, in which a chemical is added to a plate of bacteria to see if they turn purple, is a test for: a. the presence of an enzyme that breaks down hydrogen peroxide (H2O2) b. the presence of an enzyme that can convert nitrate to nitrite c. the presence of a certain protein in the bacterium’s electron transport chain d. the presence of a protein that can oxidize amino acids e. the ability of a bacterium to oxidatively use glucose, lactose, or sucrose as energy sources

2. The citrate test is shows a positive result when: a. the medium turns yellow from a starting color of red b. the medium turns red from a starting color of yellow c. the medium turns hot pink from a starting color of red d. the medium turns black from a starting color of red e. the medium turns blue from a starting color of dark green

3. Citrate-positive organisms are unique bacteria because they can specifically perform which of the following? a. use citrate metabolically b. take up citrate from the medium c. deaminate citrate d. decarboxylate citrate e. produce the enzyme citrase

4. In a positive decarboxylation test result, what molecules or substances have been decarboxylated? a. casein b. starch c. urea d. amino acids e. gelatin

5. What gas causes the foaming bubbles seen in a positive catalase test? a. oxygen b. carbon dioxide c. hydrogen d. carbon monoxide e. nitrogen

Bio 250 Lab Quiz III pg. 1 6. In the list below, select all of the enzymes that are exoenzymes. Note that if you select multiple answers, like “a” and “b”, fill in BOTH “a” and “b” on your answer sheet for this question. a. urease b. casease c. amylase d. catalase e. cytochrome c oxidase

7. In examining the results of a gelatinase test, it is essential that the control tube is: a. faintly yellow b. red c. solid d. blue e. colorless

8. The results of gelatin hydrolysis produces: a. single or short chains of amino acids b. single or short chains of glucose c. single molecules of glucose and fructose d. fatty acids e. starch

9. Indole is a chemical group that results from the catalytic break down of: a. nitrate b. urea c. any amino acid d. tryptophan e. starch

10. Which of the following media would allow the microbiologist to test for indole production? a. nutrient gelatin b. SIM media c. nitrate reduction broth d. urea agar slants e. decarboxylase broths

11. What product of bacteria metabolism causes the pH indicator dye in urease slants to turn hot pink? a. nitrite b. carbon dioxide c. acid d. ammonium e. indole

Bio 250 Lab Quiz III pg. 2 12. A bacterium that can hydrolyze casein would be able to specifically break down: a. milk b. starch c. gelatin d. urea e. glucose

13. What is the appropriate incubation time for litmus milk cultures? a. a few minutes b. 24 hours c. 48 hours d. one week e. two weeks

14. What substance must be added to a starch agar plate to interpret the results of the starch hydrolysis test? a. glucose b. iodine c. Kovac’s reagent d. hydrogen peroxide e. oxidase reagent

15. Which of the following can you NOT determine from a triple sugar iron (TSI) test? a. whether the bacteria could ferment glucose b. whether the bacteria could reduce sulfur to H2S c. whether the bacteria could reduce nitrate to nitrite d. whether the bacteria could ferment sucrose or lactose e. whether the bacteria produced acid from fermentation

16. What substance is added to sulfur-containing media in order to detect the production of hydrogen sulfide? a. iodine b. ferrous sulfate c. sodium chloride d. Kovac’s reagent e. nitrate reduction reagents ------

TRUE/FALSE Answer “a” if true and “b” if false.

17. If you were strictly looking for motility among sulfur producers in SIM media, you could eliminated the tryptophan from the medium.

18. Muller-Hinton agar, used in the Kirby-Bauer test, forms a red ring at the top when you add Kovac’s reagent.

Bio 250 Lab Quiz III pg. 3 19. A zone of clearing in the bacterial lawn around an antibiotic disk always indicates that the bacteria in the lawn are susceptible to the antibiotic.

20. The ammonia smell in baby diapers results from the hydrogen sulfide produced by intestinal bacteria. ------

5 pts. Describe the steps you would take to interpret a culture of bacteria that has been grown in nitrate reduction broth. What reagents, if any, do you add? What color-change is a positive result, and what does a “positive” mean in terms of chemical production by these bacteria (what has changed into what)? If you get a negative result, is there anything else you should do? What does it mean chemically (what has changed into what) if you now see a color change after further testing? In summary, describe all the possible outcomes, the expected color or physical changes, and what chemicals are produced for the nitrate reduction test.

Bio 250 Lab Quiz III pg. 4