Deck 6: Microbial Growth

Question 1

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 1

D

Question 2

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 2

B

Question 3

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

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

Answer 3

A

Question 4

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 5

Thirty-six colonies grew in nutrient agar from 1.0 ml of undiluted sample in a standard plate count.How many viable and culturable 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

Question 6

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

Question 7

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.

Question 8

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 9

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 10

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.

Question 11

Figure 6.2

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

Question 12

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.

Question 13

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.

Question 14

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.

Question 15

Figure 6.1

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

A)a
B)b
C)c

Question 16

Figure 6.1

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

A)a
B)b
C)c

Question 17

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

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

Question 18

Figure 6.2

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

Question 19

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 20

Most bacteria reproduce by

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

Question 21

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.

Question 22

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.

Question 23

Table 6.1
Three different culture media are shown below.

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 24

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 3 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.

Question 25

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.

Question 26

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)

Question 27

Which of the following is an organic growth factor?

A)glucose
B)vitamin B1
C)peptone
D)Mg⁺²
E)H₂O

Question 28

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

A)psychrotroph - growth at 20-30°C
B)thermophile - growth at 37°C
C)mesophile - growth at 25-40°C
D)psychrophile - growth at 15°C
E)hyperthermophiles - growth at greater than 80°C

Question 29

Three cells with generation times of 60 minutes are inoculated into a culture medium.Assuming no lag phase takes place,how many cells are there after 5 hours?

A)900
B)180
C)96
D)32
E)15

Question 30

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

Question 31

Most bacteria grow best at pH

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

Question 32

An experiment began with 4 cells in log phase and ended with 128 cells.How many generations did the cells go through?

A)64
B)32
C)6
D)5
E)4

Question 33

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

Question 34

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 35

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 36

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.

Question 37

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)

Question 38

Most fungi grow best at pH

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

Question 39

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.

Question 40

Table 6.1
Three different culture media are shown below.

In Table,6.1,in which medium (or media)would an autotroph grow but a heterotroph could not?

A)A
B)B
C)C
D)A and B
E)A and C

Question 41

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

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

Question 42

The ________ method is used to indirectly measure microbial growth of filamentous bacteria and molds.

A)metabolic activity
B)dry weight
C)pour plate
D)spread plate
E)turbidity measurement

Question 43

Most pathogenic bacteria are thermophiles.

Question 44

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

Question 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.

Question 46

Which enzyme catalyzes the following reaction? 2H₂O2 → 2H₂O + O₂

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

Question 47

The U.S.Food and Drug Administration convention when performing pour or spread plate counts is to count only plates with ________ colonies.

A)1 to 10
B)50 to 100
C)500 or more
D)25 to 250
E)30 to 300

Question 48

Filtration methods,followed by growth of the bacteria trapped on the filters in growth media,are used to count bacteria present in very low concentrations,such as in lakes and streams.

Question 49

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 50

Table 6.2 The following data show growth of two bacteria on different media.

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.

Question 51

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

Question 52

A sample of ocean water is tested for its bacterial content in a plate count assay.A one-milliliter sample of the water is diluted in a 1:10 dilution series.0.1 milliliter of the second dilution tube is plated in a pour plate.After incubation,the plate has 191 colonies,indicating that the original water sample contained

A)191 cells per milliliter.
B)1,910 cells per milliliter.
C)19,100 cells per milliliter.
D)191,000 cells per milliliter.
E)1,910,000 cells per milliliter.

Question 53

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

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

Question 54

An isolated colony on a streak plate contains millions (or even billions)of identical cells all arising from one initial cell.

Question 55

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

Question 56

In measuring turbidity of a culture in indirect measurement of bacterial growth,absorbance and transmittance are identical and interchangeable values.

Question 57

When cultivating anaerobic organisms in the laboratory setting,a candle jar is sufficient for the vast majority of organisms.

Question 58

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

Question 59

A sample of raw,unpasteurized 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 approximately 500 colonies,indicating that the original milk sample contained

A)500 cells per milliliter.
B)5,000 cells per milliliter.
C)50,000 cells per milliliter.
D)500,000 cells per milliliter.
E)The answer cannot be determined reliably with the information given.

Question 60

A sample of well water is tested for its bacterial content in a plate count assay.A one-milliliter sample of the water is diluted in a 1:10 dilution series.One milliliter of the fourth dilution tube is plated in a pour plate.After incubation,the plate has 83 colonies,indicating that the original water sample contained

A)83 cells per milliliter.
B)830 cells per milliliter.
C)8,300 cells per milliliter.
D)83,000 cells per milliliter.
E)830,000 cells per milliliter.

Question 61

A patient with a heart pacemaker received antibiotic therapy for streptococcal bacteremia (bacteria in the blood).One month later,he was treated for recurrence of the bacteremia.When he returned six weeks later,again with bacteremia,the physician recommended replacing the pacemaker.Why did this cure his condition?

Question 62

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 pure distilled 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 63

As part of an experiment where absorbance values are measured using a spectrophotometer,you are taking readings of your sample every 20 minutes.The non-motile microbe you're testing has a generation time of roughly 20 minutes at an incubation temperature right around room temperature.Things start out fine,with the expected results - as time goes by at the correct incubation temperature,absorbance starts to rise as the medium starts to become more cloudy with growing microorganisms.But roughly 2 hours into the process,you notice that the absorbance levels flatten out,and then start to decrease unexpectedly.What is most likely taking place in your experiment?

Question 64

You are tasked with attempting to culture microbes in the lab that were initially obtained from samples taken in and near the Arctic circle,in areas of extreme cold and either very long or very short days,depending on the time of year.How would you begin to try to grow these microbes in the lab,and why would you choose those methods?

Question 65

An extreme-weather event has knocked out power in your community.Even with rebuilding efforts,it appears that it could be 6 months or longer before power is restored.Since you have a background in microbiology,the people you know are asking you for possible ways of storing/preserving their food safely without electricity.What advice can you give them,and why would you make those recommendations?