Deck 6: Microbial Growth

Question 1

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) capnophiles that prefer highly oxygenated growth conditions.
D) strict aerobes that grow best in reducing media.
E) facultative anaerobes that require reducing media for growth.

Answer 1

B

Question 2

The term aerotolerant anaerobe refers to an organism that

A) tolerates normal atmospheric nitrogen gas levels.
B) requires less oxygen than is present in air.
C) does not use oxygen but tolerates it.
D) is killed by oxygen.
E) requires more oxygen than is present in air.

Answer 2

C

Question 3

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) 54,000 cells per milliliter.
B) 540,000 cells per milliliter.
C) 5,400 cells per milliliter.
D) 540 cells per milliliter.
E) 54 cells per milliliter.

Answer 3

A

Question 4

Most fungi grow best at pH

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

Question 5

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

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

Question 6

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

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

Question 7

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

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

Question 8

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

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

Question 9

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 10

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 b
B) a and d
C) c and d
D) b and d
E) a and c

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 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 12

Most bacteria grow best at pH

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

Question 13

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

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

Question 14

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) 18 per milliliter
C) 9 per milliliter
D) 36 per milliliter
E) 72 per milliliter

Question 15

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

A) phosphorus  used for production of carbohydrates.
B) nitrogen  needed for amino acid synthesis
C) sulfur  used for synthesis of thiamin and biotin
D) phosphorus  incorporated into nucleic acids
E) magnesium and potassium  required as cofactors for enzymes

Question 16

Salts and sugars work to preserve foods by creating a

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

Question 17

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

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

Question 18

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

Question 19

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

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

Question 20

Most bacteria reproduce by

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

Question 21

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

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

Question 22

Which enzyme catalyzes the reaction: 2H 2o₂ → 2H₂O + o₂?

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

Question 23

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

A) most probable number (MPN)
B) standard plate count
C) direct microscopic count
D) metabolic activity
E) filtration on a support membrane followed by incubation on medium

Question 24

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

A) glucose consumption
B) most probable number (MPN)
C) direct microscopic count
D) turbidity
E) standard plate count

Question 25

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

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

Question 26

Which enzyme catalyzes the reaction: H₂o₂ + 2H+ → 2H₂O?

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

Question 27

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

Question 28

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

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

Question 29

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

Question 30

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 31

Table 6.2 The following data show growth of two bacteria on different media.
$$\begin{array}{l}\text { Amount of Growth }\\\begin{array} { | l | c | c | } \hline & \text { Staphylococcus aureus } & \text { Streptococcus pyogenes } \\\hline \text { Nutrient agar } & + + & + + \\\hline \text { Nutrient agar } + 7.5 \% \mathrm { NaCl } & + & - \\\hline\end{array}\end{array}$$ The data in Table 6.2 indicate that S. aureus is a(n)

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

Question 32

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

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

Question 33

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 34

Which of the following is an organic growth factor?

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

Question 35

Table 6.1
Three different culture media are shown below. $\begin{array}{|l|l|l|}\hline \text { Medium A } & \text { Medium B } & \text { Medium C } \\\hline \text { Na2H PO4 } & \text { Tide detergent } & \text { Glucose } \\\hline \text { KH2PO4 } & \text { Na2HPO4 } & \text { Peptone } \\\hline \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{4} & \left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \\\hline \mathrm{CaCl}_{2} & \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{2} \\\hline \mathrm{NaHCO}_{3} & \left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} & \mathrm{Na}_{2} \mathrm{HPO}_{4} \\\hline\end{array}$

-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 36

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

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

Question 37

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.

Question 38

Which enzyme catalyzes the reaction: o₂- + o₂- + 2H+ → H₂o₂ + o₂?

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

Question 39

Table 6.1
Three different culture media are shown below. $\begin{array}{|l|l|l|}\hline \text { Medium A } & \text { Medium B } & \text { Medium C } \\\hline \text { Na2H PO4 } & \text { Tide detergent } & \text { Glucose } \\\hline \text { KH2PO4 } & \text { Na2HPO4 } & \text { Peptone } \\\hline \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{4} & \left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \\\hline \mathrm{CaCl}_{2} & \mathrm{MgSO}_{4} & \mathrm{KH}_{2} \mathrm{PO}_{2} \\\hline \mathrm{NaHCO}_{3} & \left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} & \mathrm{Na}_{2} \mathrm{HPO}_{4} \\\hline\end{array}$

-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 40

The source of nutrients in nutrient agar is

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

Question 41

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 42

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

Question 43

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

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

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

Question 46

Most pathogenic bacteria are thermophiles.

Question 47

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 48

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 49

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

Question 50

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

Question 51

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

Question 52

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.