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
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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
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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.
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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.
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