Microbiology Evolving Science 3rd Edition by Slonczewski Foster - Test Bank

Microbiology Evolving Science 3rd Edition by Slonczewski Foster – Test Bank

 

Instant Download – Complete Test Bank With Answers

 

 

Sample Questions Are Posted Below

 

CHAPTER 5: Environmental Influences and Control of Microbial Growth

 

MULTIPLE CHOICE

 

1. __________ have evolved to survive multiple extreme environments.

a.	Psychrophiles	d.	Thermophiles
b.	Extremophiles	e.	Acidophiles
c.	Halophiles

 

 

ANS:  B                    DIF:    Easy               REF:   5.1                 TOP:   I.A.ii

MSC:  Remembering

 

2. The membrane needs to remain __________ so that it can expand as cells grow larger and so proteins needed for solute transport can be inserted into the membrane.

a.	rigid	d.	hypertonic
b.	warm	e.	polarized
c.	fluid

 

 

ANS:  C                    DIF:    Easy               REF:   5.2                 TOP:   II.A

MSC:  Remembering

 

3. The general result of the Arrhenius equation is that growth rate roughly doubles for every __________°C rise in temperature.

a.	5	d.	20
b.	10	e.	25
c.	15

 

 

ANS:  B                    DIF:    Easy               REF:   5.2                 TOP:   II.A.i

MSC:  Remembering

 

4. The fastest growth rate for a species occurs at temperatures where a cell’s __________ work most efficiently.

a.	lipids	d.	proteins
b.	membranes	e.	polysaccharides
c.	nucleic acids

 

 

ANS:  D                    DIF:    Easy               REF:   5.2                 TOP:   II.A.ii

MSC:  Remembering

 

5. Human pathogens are:

a.	halophiles	d.	thermophiles
b.	psychrophiles	e.	extreme thermophiles
c.	mesophiles

 

 

ANS:  C                    DIF:    Easy               REF:   5.2                 TOP:   II.B.i

MSC:  Remembering

 

6. __________ are prominent flora beneath icebergs in the Arctic and Antarctic.

a.	Barophiles	d.	Thermophiles
b.	Psychrophiles	e.	Acidophiles
c.	Mesophiles

 

 

ANS:  B                    DIF:    Easy               REF:   5.2                 TOP:   II.B.ii

MSC:  Remembering

 

7. __________ enzymes are stable in part because they contain relatively low amounts of the amino acid glycine.

a.	Psychrophilic	d.	Halophilic
b.	Acidophilic	e.	Barophilic
c.	Thermophilic

 

 

ANS:  C                    DIF:    Medium         REF:   5.2                 TOP:   II.B.iii.a

MSC:  Remembering

 

8. __________ grow at temperatures as high as 121°C, which occur under extreme pressure.

a.	Thermophiles	d.	Hyperpsychrophiles
b.	Extreme halophiles	e.	Hyperthermophiles
c.	Psychrophiles

 

 

ANS:  E                    DIF:    Easy               REF:   5.2                 TOP:   II.B.iv

MSC:  Remembering

 

9. All of the following are true about microbes and temperature EXCEPT:

a.	Microbes have mechanisms to control their temperature.
b.	Temperature affects the average rate of molecular motion.
c.	Changes in temperature affect membrane fluidity.
d.	Changes in temperature affect transport.
e.	Every organism has an optimum temperature for growth.

 

 

ANS:  A                    DIF:    Medium         REF:   5.2                 TOP:   II.A

MSC:  Understanding

 

10. Psychrophiles favor the cold since their membranes are more fluid at low temperature as a result of the high proportion of __________ present.

a.	saturated fatty acids	d.	transport proteins
b.	unsaturated fatty acids	e.	water
c.	lipopolysaccharides

 

 

ANS:  B                    DIF:    Medium         REF:   5.2                 TOP:   II.B.ii.c

MSC:  Understanding

 

11. Which of the following is NOT true about thermophiles?

a.	Their proteins contain less glycine.
b.	They have more unsaturated linear lipids in their membranes.
c.	They have chaperone proteins.
d.	Their genomes are packed with numerous DNA-binding proteins that stabilize DNA.
e.	They have special enzymes that function to tightly coil DNA.

 

 

ANS:  B                    DIF:    Difficult         REF:   5.2                 TOP:   II.B.iii

MSC:  Understanding

 

12. Which pair of traits can the same organism have?

a.	obligate aerobe; obligate anaerobe	d.	obligate anaerobe; catalase producer
b.	Gram-positive; Gram-negative	e.	microaerophile; grows in 300 µM oxygen
c.	thermophile; facultative anaerobe

 

 

ANS:  C                    DIF:    Medium         REF:   5.2 | 5.6          TOP:   II.B.iii | VI.C

MSC:  Analyzing

 

13. Which temperature is quickly lethal to any mesophile?

a.	its optimum growth temperature	d.	refrigeration temperature
b.	its minimum growth temperature	e.	autoclave temperature
c.	its maximum growth temperature

 

 

ANS:  E                    DIF:    Easy               REF:   5.2 | 5.8          TOP:   II.B.i | VIII.C.i.b

MSC:  Remembering

 

14. Organisms adapted to grow at overwhelmingly high pressures are called:

a.	psychrophiles	d.	acidophiles
b.	thermophiles	e.	mesophiles
c.	barophiles

 

 

ANS:  C                    DIF:    Easy               REF:   5.3                 TOP:   III.A

MSC:  Remembering

 

15. Many __________ have been isolated from the ocean floor environment.

a.	psychrophiles	d.	barophiles
b.	mesophiles	e.	acidophiles
c.	thermophiles

 

 

ANS:  D                    DIF:    Easy               REF:   5.3                 TOP:   III.A

MSC:  Remembering

 

16. Piezophile is another term for:

a.	acidophile	d.	barotolerant
b.	halophile	e.	barophile
c.	psychrophile

 

 

ANS:  E                    DIF:    Easy               REF:   5.3                 TOP:   III.A

MSC:  Remembering

 

17. The pressure (psi, or pounds per square inch) at Earth’s surface is:

a.	0 psi	d.	7 psi
b.	3 psi	e.	14 psi
c.	5 psi

 

 

ANS:  E                    DIF:    Difficult         REF:   5.3                 TOP:   III.A

MSC:  Remembering

 

18. At the bottom of the ocean, hydrostatic pressure averages a crushing 400 atm (atmospheres) and can go as high as:

a.	700 atm	d.	3,000 atm
b.	1,000 atm	e.	3,500 atm
c.	1,500 atm

 

 

ANS:  B                    DIF:    Easy               REF:   5.3                 TOP:   III.A.i

MSC:  Remembering

 

19. Most bacteria require water activity to be greater than:

a.	0.10	d.	0.91
b.	0.25	e.	1.0
c.	0.74

 

 

ANS:  D                    DIF:    Easy               REF:   5.4                 TOP:   IV.A

MSC:  Remembering

 

20. __________ is a measure of the number of solute molecules in solution and is inversely related to water activity.

a.	Osmolarity	d.	Isotonic
b.	Hypertonic	e.	D-value
c.	Hypotonic

 

 

ANS:  A                    DIF:    Easy               REF:   5.4                 TOP:   IV.A.i

MSC:  Remembering

 

21. A __________ medium is one of higher osmolarity than the cell.

a.	hypertonic	d.	defined
b.	hypotonic	e.	complex
c.	isotonic

 

 

ANS:  A                    DIF:    Medium         REF:   5.4                 TOP:   IV.A.ii

MSC:  Remembering

 

22. Special channels for helping water move across the membrane quickly are called:

a.	compatible solutes	d.	mechanosensitive channels
b.	osmolarity	e.	chaperones
c.	aquaporins

 

 

ANS:  C                    DIF:    Easy               REF:   5.4                 TOP:   IV.A.iv

MSC:  Remembering

 

23. Microbes accumulate __________ in the cell to prevent cell water loss in a hypertonic environment.

a.	water	d.	protons
b.	proteins	e.	compatible solutes
c.	sugars

 

 

ANS:  E                    DIF:    Easy               REF:   5.4                 TOP:   IV.B.i.a

MSC:  Remembering

 

24. The proteins and cell components of halophiles have remarkably high intracellular levels of _________________, which helps to maintain their cell structure.

a.	oxygen	d.	sodium
b.	potassium	e.	hydrogen
c.	calcium

 

 

ANS:  B                    DIF:    Easy               REF:   5.4                 TOP:   IV.C.ii

MSC:  Remembering

 

25. The proteins and cell components of halophiles require remarkably high intracellular levels of what to maintain their structure?

a.	Ca++	d.	Na+
b.	H+	e.	S
c.	K+

 

 

ANS:  C                    DIF:    Medium         REF:   5.4                 TOP:   IV.C.ii

MSC:  Remembering

 

26. Which of the following is true of microbes and their membranes?

a.	They are relatively permeable to protons.
b.	Protons can leak through directly when the difference in intracellular and extracellular pH is very high.
c.	Membrane-permeant organic acids can prevent the leakage of protons.
d.	They are able to change the pH optima of their enzymes.
e.	Acidophiles use Na+/H+ antiporters to remove internal protons.

 

 

ANS:  B                    DIF:    Medium         REF:   5.5                 TOP:   V.A | V.C

MSC:  Remembering

 

27. __________ are commonly used to control microbial growth in foods.

a.	Weak acids	d.	Strong bases
b.	Strong acids	e.	Enzymes
c.	Weak bases

 

 

ANS:  A                    DIF:    Easy               REF:   5.5                 TOP:   V.A.iii.a

MSC:  Remembering

 

28. __________ are often chemoautotrophs that oxidize reduced metals and generate strong acids such as sulfuric acid.

a.	Acidophiles	d.	Mesophiles
b.	Psychrophiles	e.	Barophiles
c.	Halophiles

 

 

ANS:  A                    DIF:    Easy               REF:   5.5                 TOP:   V.B.ii

MSC:  Remembering

 

29. Alkaliphiles use _________________ in addition to proton motive force to maintain pH.

a.	potassium motive force	d.	magnesium motive force
b.	sodium motive force	e.	sulfur motive force
c.	calcium motive force

 

 

ANS:  B                    DIF:    Medium         REF:   5.5                 TOP:   V.B.iii

MSC:  Remembering

 

30. E. coli tolerates a pH range of 2–9, which is a what-fold difference in hydrogen ion concentration?

a.	7-fold	d.	10,000-fold
b.	100-fold	e.	10,000,000-fold
c.	1,000-fold

 

 

ANS:  E                    DIF:    Medium         REF:   5.5                 TOP:   V.A

MSC:  Understanding

 

31. A bacterium that thrives in your stomach is probably a(n):

a.	thermophile	d.	acidophile
b.	neutrophile	e.	psychrophile
c.	alkaliphile

 

 

ANS:  D                    DIF:    Easy               REF:   5.5                 TOP:   V.B.ii

MSC:  Understanding

 

32. The use of oxygen as the terminal electron acceptor is called:

a.	aerobic respiration	d.	oxygenic photosynthesis
b.	anaerobic respiration	e.	carbon dioxide fixation
c.	fermentation

 

 

ANS:  A                    DIF:    Easy               REF:   5.6                 TOP:   VI.B.i

MSC:  Remembering

 

33. Many __________ bacteria cause horrific human diseases, such as tetanus, botulism, and gangrene.

a.	aerobic	d.	halophilic
b.	anaerobic	e.	fermentative
c.	psychrophilic

 

 

ANS:  B                    DIF:    Medium         REF:   5.6                 TOP:   VI.C.i

MSC:  Remembering

 

34. Which category best describes E. coli?

a.	strict aerobe	d.	microaerophile
b.	aerotolerant anaerobe	e.	strict anaerobe
c.	facultative anaerobe

 

 

ANS:  C                    DIF:    Medium         REF:   5.6                 TOP:   VI.C.iv

MSC:  Remembering

 

35. Which of the following is NOT true of proton motive force in bacteria?

a.	It is used in the generation of energy in the form of ADP.
b.	It is used to turn the flagellar motor.
c.	It can be used for nutrient transport.
d.	It produces a transmembrane electrochemical gradient.
e.	All of the above are true.

 

 

ANS:  A                    DIF:    Medium         REF:   5.6                 TOP:   VI.A.i

MSC:  Understanding

 

36. An organism that requires full oxygen tensions of 21% for growth is:

a.	aerobic	d.	anaerobic
b.	microaerophilic	e.	facultative
c.	aerotolerant

 

 

ANS:  A                    DIF:    Easy               REF:   5.6                 TOP:   VI.B.i

MSC:  Understanding

 

37. Which best describes microaerophiles?

a.	They require atmospheric oxygen levels to grow.
b.	They cannot grow in the presence of oxygen.
c.	They will use oxygen if it is present, but can grow even if oxygen is not present.
d.	They require a small amount of oxygen.
e.	They can’t use oxygen to grow, but oxygen won’t kill them.

 

 

ANS:  D                    DIF:    Easy               REF:   5.6                 TOP:   VI.C.v

MSC:  Understanding

 

38. An organism that grows at the bottom of a tube of thioglycolate broth medium is probably a(n):

a.	strict aerobe	d.	microaerophile
b.	facultative anaerobe	e.	strict anaerobe
c.	aerotolerant anaerobe

 

 

ANS:  E                    DIF:    Easy               REF:   5.6                 TOP:   VI.D.i

MSC:  Understanding

 

39. An organism that grows at the top of a tube of thioglycolate broth medium is probably a(n):

a.	strict aerobe	d.	microaerophile
b.	facultative anaerobe	e.	strict anaerobe
c.	aerotolerant anaerobe

 

 

ANS:  A                    DIF:    Easy               REF:   5.6                 TOP:   VI.D.i

MSC:  Understanding

 

40. ____________________ is one of the important signaling molecules that controls global gene expression during starvation.

a.	Cyclic AMP	d.	Glucose
b.	ADP	e.	Water
c.	ATP

 

 

ANS:  A                    DIF:    Medium         REF:   5.7                 TOP:   VII.A.i

MSC:  Remembering

 

41. During the starvation response, most organisms can do all of the following EXCEPT:

a.	retool transport systems for the uptake of different nutrients
b.	form metabolically inactive endospores
c.	protect against reactive oxygen species
d.	protect against temperature extremes
e.	protect against pH extremes

 

 

ANS:  B                    DIF:    Medium         REF:   5.7                 TOP:   VII.A

MSC:  Understanding

 

42. Runoff from agricultural fields, lawns, and golf courses can cause an overgrowth of microbes due to:

a.	eutrophication	d.	antisepsis
b.	starvation response	e.	pasteurization
c.	oligotrophy

 

 

ANS:  A                    DIF:    Easy               REF:   5.7                 TOP:   VII.C.ii.b

MSC:  Understanding

 

43. The D-value of a bacterial culture heated to 100°C is the time it takes to kill __________% of the population.

a.	99	d.	10
b.	90	e.	1
c.	50

 

 

ANS:  B                    DIF:    Medium         REF:   5.8                 TOP:   VIII.B.i

MSC:  Remembering

 

44. Which of the following typically will survive autoclaving under standard laboratory operating conditions?

a.	mesophile	d.	Mycobacterium tuberculosis
b.	thermophile	e.	none of the above
c.	endospore former

 

 

ANS:  E                    DIF:    Easy               REF:   5.8                 TOP:   VIII.C.i

MSC:  Remembering

 

45. The conditions used in an autoclave may be reproduced at home in:

a.	a rice cooker	d.	a pressure cooker
b.	a double-boiler	e.	boiling water
c.	a microwave

 

 

ANS:  D                    DIF:    Easy               REF:   5.8                 TOP:   VIII.C.i.b

MSC:  Remembering

 

46. Which of the following uses microbes to detoxify environmental contaminants?

a.	PCR	d.	antibioisis
b.	DNA microarrays	e.	bioremediation
c.	DNA sequencing

 

 

ANS:  E                    DIF:    Easy               REF:   5.8                 TOP:   VIII.D.ii

MSC:  Remembering

 

47. Disposable plasticware such as petri dishes can be sterilized using which of the following?

a.	ethylene oxide
b.	steam autoclave
c.	low-temperature, long-time pasteurization
d.	phenol
e.	70% ethanol

 

 

ANS:  A                    DIF:    Medium         REF:   5.8                 TOP:   VIII.G

MSC:  Remembering

 

48. A virus that kills bacteria is called a:

a.	bacteriophage	d.	probiotic
b.	viroid	e.	porin
c.	spore

 

 

ANS:  A                    DIF:    Easy               REF:   5.8                 TOP:   VIII.L

MSC:  Remembering

 

49. Which of the following is NOT true concerning irradiation of foods?

a.	Food consumed by NASA astronauts is sterilized by irradiation.
b.	Foods become radioactive when irradiated.
c.	Viruses are resistant to doses approved for foods.
d.	A higher dose of radiation is necessary to kill microbes in frozen foods.
e.	It is effective in eliminating parasites and bacteria.

 

 

ANS:  B                    DIF:    Easy               REF:   5.8                 TOP:   VIII.C.v

MSC:  Understanding

 

50. The type of antimicrobial drug that would be least toxic to humans is a drug that:

a.	inhibits protein synthesis	d.	inhibits metabolic pathways
b.	disrupts the cytoplasmic membrane	e.	inhibits cell wall synthesis
c.	inhibits nucleic acid synthesis

 

 

ANS:  E                    DIF:    Medium         REF:   5.8                 TOP:   VIII.I

MSC:  Understanding

 

SHORT ANSWER

 

1. Why are thermophiles able to survive at temperatures that would quickly kill most mesophiles? Describe at least three adaptations.

 

ANS:

Thermophilic proteins are more stable due to low content of glycine residues, high number of hydrogen bonds within the protein, and large number of DNA-binding proteins compared to mesophiles. Thermophilic membranes contain more saturated fatty acids for stability. Thermophilic DNA is tightly coiled by enzymes to make it more stable and less likely to denature.

 

DIF:    Medium         REF:   5.2                 TOP:   II.B.iii            MSC:  Understanding

 

2. How are some organisms able to survive temporary exposures to elevated temperatures?

 

ANS:

Some organisms exhibit heat-shock response, which includes expression of genes for proteins that act as chaperones to stabilize proteins and enzymes that change membrane lipids to a more stable type.

 

DIF:    Medium         REF:   5.2                 TOP:   II.C                MSC:  Understanding

 

3. Why are many barophiles also psychrophiles, and how are the adaptations for barophiles and psychrophiles similar?

 

ANS:

Barophiles are typically found on the ocean floor, where high pressures exist. The average temperature of the ocean floor is 2°C; as a result, organisms found here are also psychrophiles. Both increased pressure and cold temperatures reduce membrane fluidity, so both types of organisms must have similar adaptations to keep their membranes fluid. The phospholipids have high levels of polyunsaturated fatty acids to keep membranes fluid.

 

DIF:    Medium         REF:   5.3                 TOP:   III.A.ii            MSC:  Understanding

 

4. Describe three mechanisms organisms use to reduce osmotic stress.

 

ANS:

Compatible solutes can be made or imported to increase intracellular osmolarity when cells are in hypertonic environments. Pressure-sensitive channels can allow solutes to escape when cells are in hypotonic environments. Water can cross the cell membrane either by diffusion or more quickly using aquaporins.

 

DIF:    Medium         REF:   5.4                 TOP:   IV.A | IV.B     MSC:  Understanding

 

5. Halophiles require high salt concentrations to survive. Describe a mechanism involving compatible solutes that has evolved to achieve low internal sodium ion concentrations.

 

ANS:

Cells have symporter systems that will import sodium ions with other solutes. Halophiles have evolved to require high intracellular levels of potassium ions. In fact, ribosomes actually require high levels of potassium to maintain structural integrity and function. To achieve this, halophiles have a sodium/potassium antiport system. Sodium ions are pumped out of the cell so that the compatible solute, potassium ions, may be brought into the cell.

 

DIF:    Medium         REF:   5.4                 TOP:   IV.C.ii            MSC:  Understanding

 

6. What alkaliphile do pink flamingos eat and how is it involved in making the flamingo pink?

 

ANS:

The cyanobacterium Spirulina imparts a pinkish color to the soda lakes in Africa due to a high concentration of carotene in the organism. Spirulina is the major food source of the pink flamingo. Digestive enzymes release the carotenes into the circulation, and they ultimately end up being deposited in the birds’ feathers. Flamingos would not be pink if their diet did not contain these high levels of carotene.

 

DIF:    Medium         REF:   5.5                 TOP:   V.B.iii            MSC:  Remembering

 

7. How does pH affect proteins? Why do proteins have an optimum, minimum, and maximum pH at which they will function?

 

ANS:

The charges on amino or carboxyl groups within a protein help form the intramolecular bonds that determine protein shape and protein activity. Because H⁺ concentration affects the protonation of these ionizable groups, altering pH can alter the charges on these groups, which changes protein structure and activity.

 

DIF:    Medium         REF:   5.5                 TOP:   V.A.i              MSC:  Understanding

 

8. What is a neutralophile? Neutralophiles were once referred to as neutrophiles. Why is this no longer the case?

 

ANS:

The term neutralophile refers to an organism that grows best between pH 5 and pH 8. Most human pathogens fall into this category. The term neutrophile is a descriptor for a specific type of white blood cell. So as to alleviate any confusion, neutralophile is used exclusively to designate microbes favoring an environment with a neutral pH.

 

DIF:    Medium         REF:   5.5                 TOP:   V.B.i              MSC:  Understanding

 

9. No one ever expected to find microbes thriving in our stomachs. What organism was found there, what problem does it cause, and how does it survive there?

 

ANS:

The bacterium Helicobacter pylori thrives in this acidic environment. H. pylori is the causative agent of gastric ulcers. It tolerates this acidic environment by neutralizing its microenvironment. It has very potent ureases, which generate massive amounts of ammonia. This in turn neutralizes the acidic microenvironment, allowing it to survive and thrive.

 

DIF:    Medium         REF:   5.5                 TOP:   V.C.i              MSC:  Understanding

 

10. Give an example of a naturally occurring organic acid stress situation in the food industry. How does the food industry mimic this, and why?

 

ANS:

In the yogurt-making process, lactobacilli produce lactic acid, acidifying the yogurt. This limits bacterial growth, leaving yogurt with plenty of food value. Manufacturers have added citric acid or sorbic acid to some foods to control microbial growth.

 

DIF:    Difficult         REF:   5.5 | 5.8          TOP:   V.A.iii.a | VIII.J

MSC:  Understanding

 

11. Why is oxygen so dangerous for cells and how do cells deal with these problems?

 

ANS:

Oxygen’s breakdown products are dangerously reactive. Substances such as superoxide radicals, hydrogen peroxide, and hydroxyl radicals are some of the damaging toxic oxygen products. They cause damage to DNA, RNA, proteins, and lipids. Organisms must either avoid oxygen or have ways to detoxify its breakdown products. Some organisms produce enzymes, such as superoxide dismutase, catalase, and peroxidase, to neutralize the toxic oxygen species.

 

DIF:    Difficult         REF:   5.6                 TOP:   VI.A.ii            MSC:  Understanding

 

12. Briefly describe three techniques used to culture anaerobes in the laboratory.

 

ANS:

Liquid media that contain reducing agents that eliminate dissolved oxygen can be used. Portions of the liquid below the surface will be free of oxygen and support anaerobic growth.

Agar media can be placed into anaerobic jars, which are sealed with chemicals that react with free oxygen, thus generating an anaerobic environment.

An anaerobic glove box is a sealed incubation chamber in which the atmosphere is free of oxygen.

 

DIF:    Medium         REF:   5.6                 TOP:   VI.D               MSC:  Understanding

 

13. Describe the studies with Salmonella that showed that in vitro conditions do not always model what happens in vivo (in this case in the phagocytic vacuole).

 

ANS:

Protein profiles were obtained in vitro looking at the results of single stresses. Each of these single stresses was something that would occur in the vacuole compartment. It seemed logical to hypothesize that the profile in the vacuole might correspond to the additive profiles of the single stresses in vitro, but this was not found to be the case. These studies indicate that either unique conditions are present within the vacuole or that combinations of stresses evoke new cell responses.

 

DIF:    Difficult         REF:   5.7                 TOP:   VII.B.i            MSC:  Understanding

 

14. Why is moist heat more efficient at killing microbes than dry heat? How does an autoclave kill microbes so efficiently?

 

ANS:

Moist heat is a more effective killer than dry heat because water penetrates the cells when moist heat is used. An autoclave uses moist heat under pressure to sterilize substances. The increased pressure allows the temperature to rise well above the normal boiling point of water. The standard autoclave conditions of 121°C at 15 psi for 20 minutes will sterilize substances.

 

DIF:    Medium         REF:   5.8                 TOP:   VIII.C.i.a | VIII.C.i.b

MSC:  Remembering

 

15. How is the phenol coefficient calculated? Why is phenol the standard for testing other disinfectants?

 

ANS:

Because of its potency and its history, phenol is the benchmark against which other disinfectants are measured. The phenol coefficient test involves inoculating bacteria into dilutions of the test disinfectant. At timed intervals, samples are withdrawn from each dilution and inoculated into fresh broth. The phenol coefficient is based on the highest dilution of a disinfectant that will kill all of the bacteria after 10 minutes of exposure. This concentration is known as the maximum effective dilution. Dividing the reciprocal of the maximum effective dilution for the test agent by the reciprocal of the maximum effective dilution for phenol gives the phenol coefficient.

 

DIF:    Difficult         REF:   5.8                 TOP:   VIII.F             MSC:  Remembering

 

16. Why is death a logarithmic function and not an instantaneous event upon treatment?

 

ANS:

For one thing, all cells in a population may not be at the same level of fitness. Some cells may be more susceptible than others. Another aspect is the probability of the treatment causing a lethal hit. Cells contain many different proteins and genes. Hits to one may not be as deleterious as to another. Moreover, damage must accumulate. Only after enough molecules of an essential gene or protein have been affected in a cell will it die. For these reasons, the entire population does not die immediately upon treatment; instead, it will have an exponential demise.

 

DIF:    Difficult         REF:   5.8                 TOP:   VIII.B            MSC:  Understanding

 

17. Why do some microorganisms produce antibiotics, and how do they avoid being harmed by the antibiotics they produce?

 

ANS:

Answers will vary. Microbes make antibiotics as a defense against competitors for resources such as food. To avoid being killed, the organism that produces the antibiotic may lack the molecule being targeted by the antibiotic. The antibiotic producer may also modify its own receptors so the antibiotic doesn’t bind to the producer. Others may use enzymes to modify the antibiotic if it enters the cell.

 

DIF:    Medium         REF:   5.8                 TOP:   VIII.I              MSC:  Understanding

 

18. What is biocontrol? Describe two examples.

 

ANS:

Answers will vary. Biocontrol is the use of one type of microbe to control another type. For example, probiotics are live microbes in food or supplements that are ingested to improve intestinal microbial balance. Yogurt is a specific example of a probiotic. Phage therapy is the use of viruses that kill bacteria to treat bacterial infections.

 

DIF:    Medium         REF:   5.8                 TOP:   VIII.J | VIII.K | VIII.L

MSC:  Understanding

 

19. If a disinfectant is added to a culture containing 1 x 10⁶ CFU per milliliter and the D-value of the disinfectant is 2 minutes, how many viable cells are left after 4 minutes of exposure?

 

ANS:

The D-value is the time required to kill 90% of cells (that is, the time it takes for the viable cell count to drop by one log10 unit). Since in this case, the D-value is minutes, it means that after 2 minutes, the number of viable cells will be 1 x 10⁵ CFU per milliliter and thus after 4 minutes of exposure, the number of viable cells would be 1 x 10⁴ CFU per milliliter.

 

DIF:    Medium         REF:   5.8                 TOP:   VIII.B.i          MSC:  Applying

 

20. If you have a food sample contaminated with anthrax spores, which sterilization approach would make sure the sample is free of spores without compromising the quality of the food sample—autoclaving or irradiation?

 

ANS:

Although both autoclaving and irradiation would provide a spore-free food sample at the end of process, the autoclave’s high pressure and temperature might compromise important ingredients in the food sample. However, when the food sample is irradiated, water and other intracellular molecules absorb energy and form transient reactive chemicals that damage the DNA, and thereby destroy the spores without compromising the quality of the food sample.

 

DIF:    Difficult         REF:   5.8                 TOP:   VIII.C.i | VIII.C.v

MSC:  Analyzing