General Microbiology Chapter 5

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. (True/False)

True

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. (True/False)

True

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. (True/False)

True

The rate of exponential growth varies greatly according to bacterial species and bioavailable nutrients. (True/False)

True

The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature. (True/False)

True

A ________ agent is a chemical that inhibits bacteria from reproducing, but does NOT necessarily kill them. A) bacteriostatic B) bacteriolytic C) bacteriocidal D) xerophilic

A

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

A

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.

A

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.

A

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.

A

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.

A

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

A

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.

A

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.

A

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.

A

Turbidity measurements are commonly utilized for monitoring A) planktonic cultures. B) biofilms. C) conies. D) sessile cultures.

A

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.

A

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.

A

Bacteria that are able to grow in humans and cause disease would be classified as A) psychrophiles. B) mesophiles. C) thermophiles. D) hyperthermophiles.

B

Organisms able to live in environments with high sugar concentrations are A) halotolerant. B) osmophiles. C) xerophiles. D) anaerobic fermenting bacteria.

B

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.

B

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.

B

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

B

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.

B

A chemical that denatures proteins is most likely to be classified as a(n) ________ agent. A) antiseptic B) bacteriostatic C) bacteriocidal D) detergent

C

A microbe growing in a refrigerator is likely A) psychrophilic. B) mesophilic. C) psychrotolerant or psychrophilic. D) hyperthermophilic.

C

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.

C

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.

C

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.

C

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.

C

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.

C

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

C

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

C

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.

D

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

D

A medium containing known substances in precise amounts is known as a ________ media. A) selective B) complex C) natural D) defined

D

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.

D

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

D

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.

D

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.

D

Superoxide dismutase and catalase work together to convert superoxide into A) peroxide. B) oxygen. C) water D) water and oxygen.

D

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.

D

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

D

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.

D

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

D

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.

D

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.

D

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.

D

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)

D

A bacterium such as a snow alga that is able to grow in cold temperatures is called a psychrophile. (True/False)

True

Based on studies with obligate acidophiles, high concentrations of hydrogen ions are required for their membrane stability. (True/False)

True

In both the lag and stationary phase, there is no net increase or decrease in viable cells. (True/False)

True

Knowledge of microbial growth patterns is useful in working with the control of microbial growth. (True/False)

True

Many fungi and bacteria grow best at pH 5 or below. (True/False)

True

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

True

Most microorganisms are particularly susceptible to antimicrobial agents during the logarithmic growth phase. (True/False)

True

Organisms living in boiling hot springs often grow rapidly and have short doubling times. (True/False)

True

Planktonic cells remain in suspension while sessile cells adhere to a surface. (True/False)

True

Some microbes can grow in boiling water. (True/False)

True

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

False

A bacterium whose optimal growth temperature is 35 ̊C would be classified as a thermophile. (True/False)

False

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

False

A selective medium is used to suppress the growth of certain bacteria in order to facilitate the growth of other bacteria. (True/False)

False

Autoclaving and pasteurization are two processes that are both very effective for sterilization. (True/False)

False

Direct microscopic counting of cells is an accurate method for estimating the number of viable cells in a sample. (True/False)

False

Irreversible cell damage is more likely to occur at low rather than high temperatures. (True/False)

False

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

False

Refrigeration controls microbial growth in food as a result of irreversible cell damage caused by low temperature. (True/False)

False

The death phase applies to individual cells rather than populations. (True/False)

False

The duration of exponential growth would increase if bacterial cells divided into three equal daughter cells rather than two. (True/False)

False

The optimal pH for growth of an organism refers to its intracellular environment. (True/False)

False

The optimum growth temperature for an organism is typically closer to its minimum temperature rather than the maximum temperature. (True/False)

False

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. (True/False)

False