5) In Figure 6.1, which line best depicts a psychrotroph incubated at 0°C?

A) a

B) b

C) c

Answer: B

6) If cells are grown in media containing amino acids labeled with radioactive nitrogen (15N), most of the radioactivity will be found in the cells'

A) DNA.

B) proteins.

C) phospholipids.

D) DNA and proteins.

E) DNA and phospholipids.

Answer: D

7) Which of the following elements is NOT correctly matched with its cellular function?

A) nitrogen — needed for amino acid synthesis

B) phosphorus — incorporated into nucleic acids

C) sulfur — used for synthesis of thiamin and biotin

D) magnesium and potassium — required as cofactors for enzymes

E) phosphorus — used for production of carbohydrates.

Answer: E

8) Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are

A) strict aerobes that grow best in candle jars.

B) capnophiles that grow best in carbon dioxide incubators.

C) facultative anaerobes that require reducing media for growth.

D) strict aerobes that grow best in reducing media.

E) capnophiles that prefer highly oxygenated growth conditions.

Answer: B

9) The biosafety level (BSL) for most introductory microbiology laboratories is

A) BSL-1.

B) BSL-2.

C) BSL-3.

D) BSL-4.

Answer: A

10) The biosafety level (BSL) for a clinical microbiology laboratory working with potentially airborne pathogens, such as tuberculosis bacteria, is

A) BSL-1.

B) BSL-2.

C) BSL-3.

D) BSL-4.

Answer: C

11) A sample of milk is tested for its bacterial content in a plate count assay. A one-milliliter sample of the milk is diluted in a 1:10 dilution series. One milliliter of the third dilution tube is plated in a pour plate. After incubation, the plate has 54 colonies, indicating that the original milk sample contained

A) 54 cells per milliliter.

B) 540 cells per milliliter.

C) 5,400 cells per milliliter.

D) 54,000 cells per milliliter.

E) 540,000 cells per milliliter.

Answer: D

12) The addition of which of the following to a culture medium will neutralize acids?

A) buffers

B) sugars

C) pH

D) heat

E) carbon

Answer: A

13) Salts and sugars work to preserve foods by creating a

A) depletion of nutrients.

B) hypotonic environment.

C) lower osmotic pressure.

D) hypertonic environment.

E) lower pH.

Answer: D

14) The term aerotolerant anaerobe refers to an organism that

A) does not use oxygen but tolerates it.

B) is killed by oxygen.

C) tolerates normal atmospheric nitrogen gas levels.

D) requires less oxygen than is present in air.

E) requires more oxygen than is present in air.

Answer: A

15) Which of the following is an advantage of the standard plate count?

A) can readily count cells that form aggregates

B) determines the number of viable cells

C) can be performed on very dilute samples, such as lake water

D) provides immediate results

E) can be used to count heat-sensitive bacteria

Answer: B

16) Which of the following is an advantage of the direct microscopic count?

A) can readily count organisms that are motile

B) can easily distinguish live from dead cells

C) requires no incubation time

D) sample volume is unknown

E) requires a large number of cells

Answer: C

17) Most bacteria reproduce by

A) aerial hyphae.

B) fragmentation.

C) mitosis.

D) binary fission.

E) budding.

Answer: D

18) Thirty-six colonies grew in nutrient agar from 1.0 ml of undiluted sample in a standard plate count. How many cells were in the original sample?

A) 4 per milliliter

B) 9 per milliliter

C) 18 per milliliter

D) 36 per milliliter

E) 72 per milliliter

Answer: D

19) Figure 6.2 shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture. In the figure, which section (or sections) shows a growth phase where the number of cells dying equals the number of cells dividing?
A) a
B) b
C) c
D) d
E) a and c

Answer: C

20) Figure 6.2 shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture. In the figure, which sections of the graph illustrate a logarithmic change in cell numbers?

A) a and c

B) b and d

C) a and b

D) c and d

E) a and d

Answer: B

21) Most bacteria grow best at pH

A) 1.

B) 5.

C) 7.

D) 9.

E) 14.

Answer: C

22) Most fungi grow best at pH

A) 1.

B) 5.

C) 7.

D) 9.

E) 14.

Answer: B

23) Consider a culture medium on which only gram-positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as a(n)

A) selective medium.

B) differential medium.

C) enrichment culture.

D) selective and differential medium.

E) differential and enrichment culture.

Answer: D

24) A culture medium consisting of agar, peptone, and beef heart is a

A) chemically defined medium.

B) complex medium.

C) selective medium.

D) differential medium.

E) reducing medium.

Answer: B

25) Which of the following pairs of microbe classification terms and optimal growth temperatures is mismatched?

A) psychrotroph — growth at 0°C

B) thermophile — growth at 37°C

C) mesophile — growth at 25°C

D) psychrophile — growth at 15°C

E) hyperthermophiles — growth at 85°C

Answer: B

26) During which growth phase will gram-positive bacteria be most susceptible to penicillin?

A) lag phase

B) log phase

C) death phase

D) stationary phase

E) The culture is equally susceptible during all phases.

Answer: B

27) Which of the following is the best definition of generation time?

A) the length of time needed for lag phase

B) the length of time needed for a cell to divide

C) the minimum rate of doubling

D) the duration of log phase

E) the time needed for nuclear division

Answer: B

28) Which of the following is NOT a direct method to measure microbial growth?

A) direct microscopic count

B) standard plate count

C) filtration on a support membrane followed by incubation on medium

D) metabolic activity

E) most probable number (MPN)

Answer: D

29) Which group of microorganisms is most likely to spoil a freshwater trout preserved with salt?

A) psychrophiles

B) facultative halophiles

C) anaerobes

D) thermophiles

E) hyperthermophiles

Answer: B

30) Which of the following is an organic growth factor?

A) glucose

B) vitamin B1

C) peptone

D) Mg+2

E) H2O

Answer: B

31) Which of the following is an example of a metabolic activity that could be used to measure microbial growth?

A) standard plate count

B) glucose consumption

C) direct microscopic count

D) turbidity

E) most probable number (MPN)

Answer: B

32) An experiment began with 4 cells and ended with 128 cells. How many generations did the

cells go through?

A) 64

B) 32

C) 6

D) 5

E) 4

Answer: D

33) Three cells with generation times of 60 minutes are inoculated into a culture medium. How many cells are there after 5 hours?

A) 900

B) 180

C) 96

D) 32

E) 15

Answer: C

34) In Figure 6.3, which tube shows the expected growth pattern for a microaerophile?

1. A) a
2. B) b
3. C) c
4. D) d
5. E) e

Answer: E

35) In Figure 6.3, which tube shows the expected growth pattern for a facultative anaerobe?

A) a

B) b

C) c

D) d

E) e

Answer: B

36) In one hospital, Pseudomonas aeruginosa serotype 10 infected the biliary tract of 10 percent of 1300 patients who underwent gastrointestinal endoscopic procedures. After each use, endoscopes were washed with an automatic reprocessor that flushed detergent and glutaraldehyde through the endoscopes, followed by a tap water rinse. P. aeruginosa serotype 10 was not isolated from the detergent, glutaraldehyde, or tap water. What was the source of the infections?

A) bacterial cell walls in the water

B) a biofilm in the reprocessor

C) contaminated disinfectant

D) fecal contamination of the bile ducts

E) None of the answers is correct.

Answer: B

37) For the three types of media in Table 6.1, which medium (or media) is/are chemically defined?

A) A

B) B

C) C

D) A and B

E) A and C

Answer: A

38) In Table, 6.1, in which medium (or media) would an autotroph grow?

A) A

B) B

C) C

D) A and B

E) A and C

Answer: A

39) Assume you inoculated 100 cells, with a generation time of 20 minutes, into 100 ml of nutrient broth. You then inoculated 100 cells of the same species into 200 ml of nutrient broth. After incubation for 4 hours, you can reasonably expect to have

A) more cells in the 100 ml.

B) more cells in the 200 ml.

C) the same number of cells in both.

D) The answer cannot be determined based on the information provided.

Answer: C

40) The source of nutrients in nutrient agar is

A) agar.

B) gelatin.

C) peptone and beef extract.

D) peptone and NaCl.

E) agar and NaCl.

Answer: C

41) Which enzyme catalyzes the reaction: O2- + O2- + 2H+ → H2O2 + O2?

A) catalase

B) oxidase

C) peroxidase

D) superoxide dismutase

Answer: D

42) Which enzyme catalyzes the reaction: 2H2O2 → 2H2O + O2?

A) catalase

B) oxidase

C) peroxidase

D) superoxide dismutase

Answer: A

43) Which enzyme catalyzes the reaction: H2O2 + 2H+ → 2H2O?

A) catalase

B) oxidase

C) peroxidase

D) superoxide dismutase

Answer: C

The data in Table 6.2 indicate that S. aureus is a(n)

A) mesophile.

B) facultative anaerobe.

C) facultative halophile.

D) aerobe.

E) halophile.

Answer: C

45) Patients with indwelling catheters (long-term tubes inserted into body orifices for drainage, such as through the urethra and into the urinary bladder) are susceptible to infections because

A) injected solutions are contaminated.

B) their immune systems are weakened.

C) infections can be transmitted from other people.

D) biofilms develop on catheters.

E) bacteria cause infections.

Answer: D