Deck 6: Microbial Growth

Question 1

Figure 6.1

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

A) a
B) b
C) c

Answer 1

B

Question 2

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

A) BSL- 1.
B) BSL- 2.
C) BSL- 3.
D) BSL- 4.

Answer 2

A

Question 3

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

A) oxidase
B) peroxidase
C) superoxide dismutase
D) catalase

Answer 3

C

Question 4

Table 6.1
Three different culture media are shown below. $\begin{array} { l l l } \text { Medium A } & \text { Medium B } & \text { Medium C } \\\mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 } & \text { Tide detergent } & \text { Glucose } \\\mathrm { KH } _ { 2 } \mathrm { PO } _ { 4 } & \mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 } & \text { Peptone } \\\mathrm { MgSO } _ { 4 } & \mathrm { KH } _ { 2 } \mathrm { PO } _ { 4 } & \left( \mathrm { NH } _ { 4 } \right) _ { 2 } \mathrm { SO } _ { 4 } \\\mathrm { CaCl } _ { 2 } & \mathrm { MgSO } _ { 4 } & \mathrm { KH } _ { 2 } \mathrm { PO } _ { 2 } \\\mathrm { NaHCO } _ { 3 } & \left( \mathrm { NH } _ { 4 } \right) _ { 2 } \mathrm { SO } _ { 4 } & \mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 }\end{array}$

-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

Question 5

Figure 6.1

In Figure 6.1, which line best depicts a facultative anaerobe in the absence of O₂?

A) a
B) b
C) c

Question 6

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

A) phosphorus - incorporated into nucleic acids
B) magnesium and potassium - required as cofactors for enzymes
C) nitrogen - needed for amino acid synthesis
D) sulfur - used for synthesis of thiamin and biotin
E) None of the answers is correct; all of the elements are correctly matched.

Question 7

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

A) sample volume is unknown
B) requires a large number of cells
C) requires no incubation time
D) can easily distinguish live from dead cells
E) can readily count organisms that are motile

Question 8

Figure 6.1

In Figure 6.1, which line best illustrates the growth of a facultative anaerobe incubated aerobically?

A) a
B) b
C) c

Question 9

The term aerotolerant anaerobe refers to an organism that

A) requires less oxygen than is present in air.
B) is killed by oxygen.
C) requires more oxygen than is present in air.
D) uses oxygen or grows without oxygen.
E) does not use oxygen but tolerates it.

Question 10

Figure 6.3

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

A) a
B) b
C) c
D) d
E) e

Question 11

Most fungi grow best at pH

A) 1.
B) 5.
C) 7.
D) 9.
E) 14.

Question 12

Figure 6.1

In Figure 6.1 ,which line best depicts an obligate anaerobe in the presence of O₂?

A) a
B) b
C) c

Question 13

Figure 6.1

In Figure 6.1, which line shows the growth of an obligate aerobe incubated anaerobically?

A) a
B) b
C) c

Question 14

Assume you inoculated 100 cells into 100 ml of nutrient broth. You then inoculated 100 cells of the same species into 200 ml of nutrient broth. After incubation for 24 hours, you should have

A) the same number of cells in both.
B) more cells in the 100 ml.
C) more cells in the 200 ml.
D) The answer cannot be determined based on the information provided.

Question 15

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

A) capnophiles that grow best in carbon dioxide incubators.
B) capnophiles that prefer highly oxygenated growth conditions.
C) strict aerobes that grow best in candle jars.
D) facultative anaerobes that require reducing media for growth.
E) strict aerobes that grow best in reducing media.

Question 16

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

A) facultative halophiles
B) anaerobes
C) hyperthermophiles
D) psychrophiles
E) thermophiles

Question 17

A culture medium on which only gram- positive organisms grow and a yellow halo surrounds Staphylococcus aureus colonies is called a(n)

A) enrichment culture.
B) differential medium.
C) selective medium.
D) selective and differential medium.
E) differential and enrichment culture.

Question 18

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

A) glucose consumption
B) turbidity
C) MPN
D) standard plate count
E) direct microscopic count

Question 19

The source of nutrients in nutrient agar is

A) agar.
B) nutrient.
C) peptone and beef extract.
D) peptone and NaCl.
E) agar and NaCl.

Question 20

Figure 6.3

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

Question 21

Which of the following is an organic growth factor?

A) H₂O
B) glucose
C) vitamin B1
D) NH₄H₂PO₄
E) peptone

Question 22

Which enzyme catalyzes the reaction: H₂O₂ + 2H⁺ -2H₂O?

A) superoxide dismutase
B) peroxidase
C) catalase
D) oxidase

Question 23

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.
B) 540 cells.
C) 5400 cells.
D) 54,000 cells.
E) 540,000 cells.

Question 24

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

A) DNA.
B) proteins.
C) phospholipids.
D) DNA and proteins.
E) DNA and phospholipids.

Question 25

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

A) metabolic activity
B) filtration
C) standard plate count
D) most probable number (MPN)
E) direct microscopic count

Question 26

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
B) 9
C) 18
D) 36
E) 72

Question 27

Patients with indwelling catheters are susceptible to infections because

A) infections can be transmitted from other people.
B) bacteria cause infections.
C) biofilms develop on catheters.
D) injected solutions are contaminated.
E) their immune systems are weakened.

Question 28

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 10 was not isolated from the detergent, glutaraldehyde, or tap water. What was the source of the infections?

A) a biofilm in the reprocessor
B) fecal contamination of the bile ducts
C) contaminated disinfectant
D) bacterial cell walls in the water
E) None of the answers is correct.

Question 29

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

A) the length of time needed for lag phase
B) the duration of log phase
C) the minimum rate of doubling
D) the time needed for nuclear division
E) the length of time needed for a cell to divide

Question 30

Figure 6.2

Figure 6.2 shows a typical bacterial growth curve with the x- axis indicating the log of the number of bacteria and the y- 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

Question 31

Most bacteria grow best at pH

A) 1.
B) 5.
C) 7.
D) 9.
E) 14.

Question 32

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

A) buffers
B) heat
C) sugars
D) carbon
E) pH

Question 33

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

A) provides immediate results
B) determines the number of viable cells
C) can be used to count heat- sensitive bacteria
D) can be performed on very dilute samples, such as lake water
E) can readily count cells that form aggregates

Question 34

Figure 6.2

Figure 6.2 shows a typical bacterial growth curve with the x- axis indicating the log of the number of bacteria and the y- 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

Question 35

Which of the following pairs is mismatched?

A) mesophile - growth at 25°C
B) thermophile - growth at 37°C
C) psychrophile - growth at 15°C
D) hyperthermophiles - growth at 85°C
E) psychrotroph - growth at 0°C

Question 36

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

A) death phase
B) log phase
C) lag phase
D) stationary phase
E) The culture is equally susceptible during all phases.

Question 37

Which enzyme catalyzes the reaction: 2H₂O2 -2H₂O + O₂?

A) superoxide dismutase
B) catalase
C) oxidase
D) peroxidase

Question 38

Salts and sugars work to preserve foods by creating a

A) hypotonic environment.
B) hypertonic environment.
C) lower osmotic pressure.
D) depletion of nutrients.
E) lower pH.

Question 39

Most bacteria reproduce by

A) budding.
B) aerial hyphae.
C) mitosis.
D) binary fission.
E) fragmentation.

Question 40

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

Question 41

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

A) chemically defined medium.
B) reducing medium.
C) selective medium.
D) complex medium.
E) differential medium.

Question 42

In performing a ten- fold dilutions series from a sample containing 10,000 bacteria per milliliter, the fourth tube in the dilution series will have 10 cells per milliliter.

Question 43

Table 6.3

Bacterial generation times for four different bacterial species were calculated in the media listed in Table 6.3. All media were prepared with tap water and incubated aerobically in the light. Compare and contrast the growth requirements of the four bacteria listed above. Which of the media, if any, are chemically defined?

Question 44

Most pathogenic bacteria are thermophiles.

Question 45

Filtration methods are used to count bacteria present in very low concentrations, such as in lakes and streams.

Question 46

Table 6.1
Three different culture media are shown below. $\begin{array} { l l l } \text { Medium A } & \text { Medium B } & \text { Medium } \mathrm { C } \\\mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 } & \text { Tide detergent } & \text { Glucose } \\\mathrm { KH } _ { 2 } \mathrm { PO } _ { 4 } & \mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 } & \text { Peptone } \\\mathrm { MgSO } _ { 4 } & \mathrm { KH } _ { 2 } \mathrm { PO } _ { 4 } & \left( \mathrm { NH } _ { 4 } \right) _ { 2 } \mathrm { SO } _ { 4 } \\\mathrm { CaCl } _ { 2 } & \mathrm { MgSO } _ { 4 } & \mathrm { KH } _ { 2 } \mathrm { PO } _ { 2 } \\\mathrm { NaHCO } _ { 3 } & \left( \mathrm { NH } _ { 4 } \right) _ { 2 } \mathrm { SO } _ { 4 } & \mathrm { Na } _ { 2 } \mathrm { HPO } _ { 4 }\end{array}$

-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

Question 47

Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it.

Question 48

Laboratory cultivation of obligate anaerobes requires reducing media or special growth chambers filled with inert gases.

Question 49

Table 6.2
The following data show growth of two bacteria on different media.
$$\begin{array}{l}\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\text { Amount of Growth }\\\begin{array} { | l | c | c | } \hline & \text { Staphylococcus avoeus } & \text { Streptococcus pyogenes } \\\hline \text { Nutrient agar } & + + & + + \\\hline \text { Nutrient agar + 7.5\% NaCl } & + & - \\\hline\end{array}\end{array}$$

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

A) facultative halophile.
B) aerobe.
C) facultative anaerobe.
D) halophile.
E) mesophile.

Question 50

Turbidity is an indirect measurement of bacterial growth that can be measured using a spectrophotometer.

Question 51

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

Question 52

Pure cultures can easily be obtained on streak plates, even if the desired bacteria are present in very low concentrations.

Question 53

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.

Question 54

Figure 6.4

In each graph in Figure 6.4, the culture was incubated at 30°C in glucose- minimal salts broth, aerobically. The bacterium is a facultative anaerobe with an optimum temperature of 37°C and can metabolize glucose and lactose. Indicate how each growth curve would change under the conditions indicated in each graph. Draw the new graphs, or write "no change."

Question 55

Bacterial growth refers to an increase in the numbers of cells in a bacterial culture.

Question 56

An isolated colony on a streak plate contains millions or billions of identical cells.

Question 57

Nitrogen- fixing bacteria, such as cyanobacteria, can use atmospheric nitrogen (N₂) for their nitrogen source.