Deck 5: Microbial Growth and Its Control

Question 1

Most mesophilic organisms can grow in a temperature range of

A) 0-15°C.
B) 10-20°C.
C) 20-45°C.
D) 50-65°C.

Answer 1

C

Question 2

Bacteria that are able to grow in humans and cause disease would be classified as

A) psychrophiles.
B) mesophiles.
C) thermophiles.
D) hyperthermophiles.

Answer 2

B

Question 3

Cell density in a chemostat is controlled by

A) the concentration of the limiting nutrient.
B) the dilution factor.
C) the size of the initial inoculum.
D) the concentration of the limiting nutrient, the dilution factor, and the size of the initial inoculum.

Answer 3

A

Question 4

The time between inoculation and the beginning of growth is usually called the

A) lag phase.
B) log phase.
C) dormant phase.
D) death phase.

Question 5

The ratio of the vapor pressure of the air in equilibrium with a substance to the vapor pressure of pure water is known as

A) water activity.
B) vapor activity.
C) positive water balance.
D) osmosis.

Question 6

Which of the following is/are transferred to daughter cells during bacterial cell division?

A) only genomic DNA, the blueprint for everything the cell needs
B) individual genes and enzymes to later be brought together to form the genome
C) only the chromosome and enzymes to immediately begin cellular metabolism
D) chromosome, proteins, and all other cellular constituents

Question 7

Bacterial growth refers to

A) an increase in the number of cells.
B) the occurrence of binary fission.
C) the time required for one cell to divide into two.
D) the occurrence of mitosis.

Question 8

Relative to enzymes in mesophilic microorganisms, which of the following is NOT characteristic of enzymes in psychrophiles?

A) decreased alpha helix content
B) decreased beta sheet content
C) fewer hydrogen bonds
D) fewer ionic bonds

Question 9

A chemical that denatures proteins is most likely to be classified as a(n) ________ agent.

A) antiseptic
B) bacteriostatic
C) bacteriocidal
D) detergent

Question 10

An agar plate for counting colonies and maximizing statistical validity should ideally contain

A) 1 to 100 colonies.
B) 50 to 100 colonies.
C) 30 to 300 colonies.
D) 100 to 1000 colonies.

Question 11

Turbidity measurements are commonly utilized for monitoring

A) planktonic cultures.
B) biofilms.
C) conies.
D) sessile cultures.

Question 12

A microbe growing in a refrigerator is likely

A) psychrophilic.
B) mesophilic.
C) psychrotolerant or psychrophilic.
D) hyperthermophilic.

Question 13

The time interval required for the formation of two cells from one is called the

A) generation time.
B) growth time.
C) growth rate.
D) division rate.

Question 14

Optical density and viable cell concentration are LEAST proportional to each other during the

A) lag phase.
B) exponential growth phase.
C) stationary phase.
D) death phase.

Question 15

Obligate anaerobes which are sensitive to O₂ would be found growing

A) throughout a tube of thioglycolate broth.
B) only at the very top of a tube of thioglycolate broth.
C) only at the bottom of a tube of thioglycolate broth.
D) approximately one-third of the way down the thioglycolate broth.

Question 16

The number of colonies obtained in a plate count does NOT depend on the

A) inoculum volume.
B) size of the colonies.
C) type of culture medium.
D) incubation time.

Question 17

When attempting to determine viable cell counts of a heat-sensitive bacterial isolate, which cell counting method should be avoided?

A) spread-plate method
B) pour-plate method
C) live staining and direct counting with a microscope
D) both spread- and pour-plate methods

Question 18

Organisms able to live in environments with high sugar concentrations are

A) halotolerant.
B) osmophiles.
C) xerophiles.
D) anaerobic fermenting bacteria.

Question 19

Which of these statements is/are TRUE?

A) In general, species that can grow at higher temperatures are prokaryotic.
B) The most thermophilic prokaryotes are species of Archaea.
C) Chemoorganotrophic organisms are able to grow at higher temperatures than phototrophic organisms.
D) All of the statements are true.

Question 20

What temperature is most commonly used in autoclaves to sterilize growth media and other devices prior to experimentation?

A) 95°C
B) 101°C
C) 121°C
D) 140°C

Question 21

Serial dilutions are generally made

A) when the appropriate viable count is unknown.
B) based on powers of 10, although other serial dilution factors are possible.
C) to reach a suitable dilution while minimizing error.
D) All of these answer choices apply.

Question 22

When water activity is low, an organism must

A) increase its internal solute concentration.
B) increase its external solute concentration.
C) decrease its internal solute concentration.
D) decrease its external solute concentration.

Question 23

A ________ agent is a chemical that inhibits bacteria from reproducing, but does NOT necessarily kill them.

A) bacteriostatic
B) bacteriolytic
C) bacteriocidal
D) xerophilic

Question 24

A halotolerant facultative anaerobe would grow BEST in which of the following environments?

A) oxygen depleted saline
B) oxygenated saline
C) oxygen depleted non-saline
D) oxygenated non-saline

Question 25

Superoxide dismutase and catalase work together to convert superoxide into

A) peroxide.
B) oxygen.
C) water
D) water and oxygen.

Question 26

Which of the following methods used to enumerate cells often requires specialized staining to observe non-pigmented bacteria?

A) spectrophotometry/turbidity
B) spread-plating
C) microscopy
D) spread-plating, turbidity, and microscopy

Question 27

Which method would be LEAST effective at sterilizing a glass hockey stick to use in the spread-plate method?

A) autoclaving
B) gamma radiation
C) ethanol soaking
D) ultrahigh-temperature pasteurization

Question 28

The cell membranes of thermophiles and hyperthermophilic bacteria typically have

A) more saturated fatty acids.
B) more long chain fatty acids.
C) fewer unsaturated fatty acids.
D) All of these answer choices are true of thermophiles and hyperthermophilic bacteria.

Question 29

Selective medium differs from differential medium because

A) selective medium permits growth of more organisms than differential medium.
B) selective medium permits growth of a particular microbial type while differential medium is used to distinguish between types of organisms.
C) differential medium differentiates pathogens from nonpathogens while selective medium grows only pathogens.
D) differential medium contains growth inhibitors while selective medium does not.

Question 30

Which term is most relevant in describing the efficacy of an antimicrobial for use in a clinical setting?

A) effective dose
B) sterilization coefficient
C) lethal dosage
D) minimum inhibitory concentration (MIC)

Question 31

The optimal growth temperature of a bacterium is most closely related to the optimal temperature for

A) transcription of DNA.
B) DNA replication.
C) enzyme function.
D) mRNA attachment to ribosomes.

Question 32

A medium containing known substances in precise amounts is known as a ________ media.

A) selective
B) complex
C) natural
D) defined

Question 33

When counting colonies on an agar plate

A) it is assumed that each colony arose from division of one or a few cells.
B) only viable colonies are counted.
C) the medium must be suitable for colony growth.
D) All of these answer choices are true.

Question 34

Which of the following statements is TRUE of disinfectants?

A) They are always effective in destroying endospores.
B) They are used on living tissue.
C) They are used for sterilization.
D) They are used on inanimate surfaces.

Question 35

Why is the enzyme catalase important to the survival of bacteria?

A) Catalase protects the cell from desiccation.
B) Catalase breaks down toxic hydrogen peroxide.
C) Catalase allows for growth in high salt concentrations.
D) Catalase aids in the transport of oxygen into the cell.

Question 36

By controlling the concentration of nutrients continuously added to a chemostat, cells can constantly be maintained at the

A) exponential growth phase.
B) stationary growth phase.
C) lag growth phase.
D) death growth phase.

Question 37

Which of the following forms of oxygen is/are generally toxic to living organisms?

A) superoxide anion
B) hydrogen peroxide
C) hydroxyl radical
D) Superoxide, hydrogen peroxide, and hydroxyl radicals are all toxic.

Question 38

A bacterium possessing ________ will produce O₂ bubbles when placed in the presence of hydrogen peroxide.

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

Question 39

The use of chemical agents directly on exposed body surfaces to destroy or inhibit vegetative pathogens is

A) disinfection.
B) sterilization.
C) antisepsis.
D) sanitization.

Question 40

Which of the following statements is FALSE?

A) In the death phase, bacterial growth may cease as a result of oxygen and nutrient depletion.
B) The generation time of bacteria may vary from species to species.
C) Bacteria typically divide by binary fission, producing two daughter cells.
D) In the lag phase, cell death exceeds cell division.

Question 41

The death phase applies to individual cells rather than populations.

Question 42

A complex medium is one that has been completely made in the laboratory and the concentration of all the nutrients is known.

Question 43

In both the lag and stationary phase, there is no net increase or decrease in viable cells.

Question 44

Microbial growth is generally described as an increase in cell number rather than the expansion in size of an individual microbial cell.

Question 45

A microbiology student in a research lab repeated an experiment described by others using the identical bacterial isolate, the same growth medium, and the same growth conditions. However, the student was unable to achieve the same O.D. at 600 nm. What is the LEAST likely cause for this discrepancy in measured turbidity?

A) One experiment used 16 mm wide test tubes while the other used 18 mm wide test tubes.
B) One experiment subtracted the yellow color of the growth medium away from the final turbidity reported whereas the other used colorless water.
C) One experiment vigorously dispersed the bacterial pellicle with vortexing while the other did not.
D) The two experiments were carried out at vastly different elevations and did not consider the influence of pressure.

Question 46

The rate of exponential growth varies greatly according to bacterial species and bioavailable nutrients.

Question 47

When viable cell concentrations are too high to count on an agar plate, it is common to use larger sized plates to increase the surface area for counting the colonies.

Question 48

Microbial contamination is prevented by the

A) use of the quadrant streak method.
B) use of aseptic technique.
C) use of cultures containing special nutrients.
D) spread plate method.

Question 49

A bacterium such as a snow alga that is able to grow in cold temperatures is called a psychrophile.

Question 50

A common antimicrobial chemical (or chemicals) used as both an antiseptic and a general disinfectant is

A) iodophors.
B) 70% alcohol.
C) hydrogen peroxide.
D) Each of these chemicals at appropriate concentrations can be used as antiseptics or disinfectants.

Question 51

The optimum growth temperature for an organism is typically closer to its minimum temperature rather than the maximum temperature.

Question 52

Direct microscopic counting of cells is an accurate method for estimating the number of viable cells in a sample.

Question 53

The lag phase does NOT occur if an exponentially growing culture is transferred into a nutrient rich medium with the same components and growth conditions as the previous medium.

Question 54

Cultures of a bacterial species were incubated on the shelf of a refrigerator (5°C), on a lab benchtop (25°C), on the shelf of a 37°C incubator, and on the shelf of a 50°C incubator. After incubation, there was no growth at 37°C or 50°C, slight growth on the benchtop, and abundant growth at refrigeration. What term could be used for this species?

A) halophile
B) mesophile
C) anaerobe
D) psychrophile

Question 55

Many fungi and bacteria grow best at pH 5 or below.

Question 56

A bacterium whose optimal growth temperature is 35˚C would be classified as a thermophile.

Question 57

Refrigeration controls microbial growth in food as a result of irreversible cell damage caused by low temperature.

Question 58

The optimal pH for growth of an organism refers to its intracellular environment.

Question 59

A selective medium is used to suppress the growth of certain bacteria in order to facilitate the growth of other bacteria.

Question 60

The duration of exponential growth would increase if bacterial cells divided into three equal daughter cells rather than two.

Question 61

Enumerating the viable and total cell concentration of a population of a microbial isolate can be a laborious task for a microbiologist, especially when studying the same isolate for several years. It is often more practical to determine the relationship between optical density (OD) and cell concentration. Once this relationship (determined by a standard curve) is determined, the OD of an isolate in a broth can be used to determine the populationʹs concentration. Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve.

Question 62

Mesophiles typically have longer fatty acid tails and more saturated carbon-carbon bonds in their cytoplasmic tails compared with thermophiles.

Question 63

Explain the difference between the division rate and the generation time.

Question 64

Some microbes can grow in boiling water.

Question 65

Based on studies with obligate acidophiles, high concentrations of hydrogen ions are required for their membrane stability.

Question 66

Sterility of a laminar flow hood is accomplished by filter-sterilized air passed through the hood quickly enough that non-sterile air does not flow into the work area.

Question 67

Irreversible cell damage is more likely to occur at low rather than high temperatures.

Question 68

The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature.

Question 69

Explain the present understanding of molecular adaptations to the cytoplasmic membrane as found in psychrophiles.

Question 70

Organisms living in boiling hot springs often grow rapidly and have short doubling times.

Question 71

Autoclaving and pasteurization are two processes that are both very effective for sterilization.

Question 72

Planktonic cells remain in suspension while sessile cells adhere to a surface.

Question 73

Knowing the concentration of microorganisms in a sample is often an important consideration for environmental, industrial, and medical microbiologists, yet a microscope is sometimes not used to accomplish this task. Explain five major limitations to using a light microscope to directly count microorganisms.

Question 74

Explain why a hyperthermophile is unlikely to be a human pathogen.

Question 75

Most microorganisms are particularly susceptible to antimicrobial agents during the logarithmic growth phase.

Question 76

A bacterial cell in nutrient broth with a generation time of 15 minutes will produce 16 cells in 2 hours.

Question 77

Knowledge of microbial growth patterns is useful in working with the control of microbial growth.

Question 78

Compare and contrast the spread plate method and the pour plate method of doing plate counts. Also describe which group of organisms would not be quantifiable in the pour plate method but would still be observed in the spread plate method.

Question 79

Use the formulas N = N₀2ⁿ and g = t/n.
N = final cell number, N₀ = initial cell number,
n = number of generations, t = time, g = generation time.
Find the generation time if N = 2 × 10⁸, N₀ = 3 × 10⁶ and t = 3 hours.

Question 80

Taq polymerase was isolated from a thermophile and is used in the polymerase chain reaction (PCR) technique because it does not become inactivated at high temperatures.