Test bank for 2013 microbiology with diseases by taxonomy, 4th edition

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Exam

Name___________________________________

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Alcohols are used for
A) antisepsis.
B) sterilization.
C) disinfection.
D) both sterilization and disinfection.
E) both antisepsis and disinfection.
Answer: E
Explanation:

1)

A)
B)
C)
D)
E)

2) Which of the following infectious agents is least resistant to destruction by chemical methods?
A) enveloped viruses
B) fungal spores
C) nonenveloped viruses
D) vegetative bacterial cells
E) bacterial endospores
Answer: A

Explanation:

A)
B)
C)
D)
E)

3) Which of the following is used for microbial control in fresh fruits and vegetables?
A) gamma rays
B) ultraviolet light
C) microwaves
D) electron beams
E) X-rays
Answer: A
Explanation:

2)

A)
B)
C)
D)
E)

1

3)

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4) Which of the following was used in the past to prevent the transmission of gonorrhea from an
infected mother to her newborn?
A) silver nitrate
B) hydrogen peroxide
C) beta-propiolactone
D) hexachlorophene
E) thimerosal
Answer: A
Explanation:

A)
B)
C)
D)
E)

5) Which of the following statements is TRUE of disinfectants?
A) They are only effective for short periods of time (seconds to minutes).
B) They are effective in destroying endospores.
C) They are used on inanimate surfaces.
D) They are used on living tissue.
E) They are used for sterilization.
Answer: C
Explanation:

5)

A)
B)

C)
D)
E)

6) An instrument that will come into contact with only the skin of a patient should be disinfected with
a(n)
A) degerming agent only.
B) low-level germicide.
C) germistatic agent only.
D) intermediate-level germicide.
E) high-level germicide.
Answer: B
Explanation:

4)

A)
B)
C)
D)
E)

2

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7) Which of the following statements about quaternary ammonium compounds is FALSE?
A) They are harmless to humans except at high concentrations.

B) They function by cross-linking proteins.
C) They are a type of detergent.
D) Zephiran is an example of a quat.
E) They are not effective against Pseudomonas aeruginosa.
Answer: B
Explanation:

A)
B)
C)
D)
E)

8) Which of the following is a target of pasteurization?
A) Brucella melitensis
B) Neisseria gonorrhoeae
C) Chlamydia trachomatis
D) Bacillus stearothermophilus
E) Clostridium botulinum
Answer: A
Explanation:

9)

A)
B)
C)
D)
E)

10) Which of the following statements about aldehydes is FALSE?
A) They denature proteins.
B) They are usually hazardous to humans.
C) Some aldehydes can sterilize after long periods of exposure.
D) They are used only to preserve dead tissues.
E) They are used in aqueous solutions.
Answer: D
Explanation:

8)

A)
B)
C)
D)
E)

9) Gamma irradiation is a process for
A) sterilization.
B) antisepsis.
C) degerming.
D) disinfection.
E) both antisepsis and disinfection.
Answer: A
Explanation:

7)

A)
B)

C)
D)
E)

3

10)


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11) Which of the following is a sterilizing agent?
A) peracetic acid
B) ozone and hydrogen peroxide
C) hydrogen peroxide
D) ozone
E) dish soap
Answer: A
Explanation:

11)

A)
B)
C)
D)
E)

12) Which of the following types of radiation is nonionizing and has the shortest wavelength?
A) gamma rays
B) ultraviolet light

C) infrared radiation
D) X-rays
E) microwaves
Answer: B
Explanation:

A)
B)
C)
D)
E)

13) Which of the following describes flash pasteurization?
A) heating at 72°C for 15 minutes
B) heating at 72°C for 15 seconds
C) heating at 134°C for one second
D) passing liquid through steam at 140°C
E) heating at 63°C for 30 minutes
Answer: B
Explanation:

13)

A)
B)
C)
D)
E)

14) Glutaraldehyde is used for

A) sterilization
B) sanitization.
C) disinfection.
D) antisepsis.
E) both disinfection and sterilization.
Answer: E
Explanation:

12)

14)

A)
B)
C)
D)
E)

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15) The process of filtration is a(n)
A) disinfectant method.
B) ineffective method for removing microbes.
C) sanitization method.
D) sterilizing method.
E) antiseptic procedure.
Answer: D
Explanation:

15)

A)
B)
C)
D)
E)

16) The endospores of which of the following microbes are used to measure the effectiveness of
autoclave sterilization?
A) Mycobacterium bovis
B) Clostridium botulinum
C) Bacillus stearothermophilus
D) Pseudomonas aeruginosa
E) Neisseria gonorrhoeae
Answer: C
Explanation:

A)
B)
C)
D)
E)

17) Which of the following would be used to sterilize a mattress?
A) heavy metals
B) ethylene oxide
C) formaldehyde
D) radiation

E) autoclaving
Answer: B
Explanation:

17)

A)
B)
C)
D)
E)

18) Which of the following is NOT a feature associated with filtration?
A) use of HEPA filters to filter air
B) ability of some filters to trap viruses and proteins
C) nitrocellulose or plastic membrane filters
D) sterilization of heat-sensitive materials
E) varying thicknesses of membrane filters used
Answer: E
Explanation:

16)

A)
B)
C)
D)
E)
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19) Disinfecting agents naturally produced by microorganisms are
A) aldehydes.
B) triclosans.
C) quats.
D) halogens.
E) antimicrobials.
Answer: E
Explanation:

A)
B)
C)
D)
E)

20) Boiling water for 10 minutes is effective in ridding it of
A) protozoan cysts.
B) enveloped viruses.
C) actively growing bacteria.
D) bacterial endospores.
E) both growing bacteria and enveloped viruses.
Answer: E
Explanation:

20)

A)
B)
C)
D)
E)

21) Which of the following can be used to disinfect air?
A) HEPA filters
B) ultraviolet light
C) ethylene oxide
D) both HEPA filters and ultraviolet light
E) both ethylene oxide and ultraviolet light
Answer: D
Explanation:

19)

21)

A)
B)
C)
D)
E)

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22) A stationary broth culture contains 10 billion (1010) cells. The microbial death rate during

autoclaving of this spent culture is 1.5 minutes. How long must it be autoclaved to be considered
sterile?
A) 10 minutes
B) 9 minutes
C) 12 minutes
D) 16.5 minutes
E) 20 minutes
Answer: D
Explanation:

A)
B)
C)
D)
E)

23) Which of the following is the most difficult to inactivate?
A) fungus spores
B) bacterial endospores
C) protozoal cysts
D) nonenveloped viruses
E) enveloped viruses
Answer: B
Explanation:

23)

A)
B)
C)

D)
E)

24) ________ is the physical removal of microbes.
A) Antisepsis
B) Sanitization
C) Disinfection
D) Sterilization
E) Degerming
Answer: E
Explanation:

22)

24)

A)
B)
C)
D)
E)

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25) Antimicrobial agents that damage nucleic acids also affect
A) the cell membrane.
B) the cell wall.
C) protein synthesis.

D) endospores.
E) the viral envelope.
Answer: C
Explanation:

A)
B)
C)
D)
E)

26) ________ may be achieved using chlorine dioxide.
A) Sterilization
B) Degerming
C) Antisepsis
D) Disinfection
E) Both antisepsis and degerming
Answer: D
Explanation:

26)

A)
B)
C)
D)
E)

27) A scientist develops a new medication that is a protein compound and that must be administered
by injection. Which of the following would be the most effective and safest means of preparing a

sterile solution of the new medication?
A) filtration
B) autoclaving
C) dilution with alcohol
D) ultraviolet irradiation
E) lyophilization
Answer: A
Explanation:

25)

A)
B)
C)
D)
E)

8

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28) Which of the following is used to sterilize items that should not, or cannot, be exposed to heat or
water?
A) hydrogen peroxide
B) ethylene oxide
C) calcium hypochlorite
D) triclosan
E) formaldehyde

Answer: B
Explanation:

A)
B)
C)
D)
E)

29) Silvadene, a topical treatment for burns, contains 1% silver. What category of chemical control
agent is in Silvadene?
A) halogens
B) aldehydes
C) oxidizing agents
D) heavy metals
E) surfactants
Answer: D
Explanation:

29)

A)
B)
C)
D)
E)

30) The chemical agents known as "quats" are used for
A) sterilization.
B) quantifying antimicrobial activity.

C) neither antisepsis nor disinfection.
D) disinfection.
E) antisepsis.
Answer: D
Explanation:

28)

30)

A)
B)
C)
D)
E)

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31) The use of lysozyme during the preparation of cheeses and wines is effective in reducing the
numbers of
A) all microbes.
B) bacteria.
C) fungi.
D) viruses.
E) prions.
Answer: B
Explanation:

A)
B)
C)
D)
E)

32) A chemical agent that kills pathogenic microbes in general is a(n)
A) disinfectant.
B) antiseptic.
C) fungicide.
D) germicide.
E) sanitizer.
Answer: D
Explanation:

33)

A)
B)
C)
D)
E)

34) The compound ethylene oxide is used in
A) sanitization.
B) disinfection.
C) sterilization.
D) degerming.
E) antisepsis.
Answer: C

Explanation:

32)

A)
B)
C)
D)
E)

33) Which of the following antimicrobial agents is the most toxic to humans?
A) 70% alcohol
B) ethylene oxide
C) iodophors
D) chloramines
E) quats
Answer: B
Explanation:

31)

34)

A)
B)
C)
D)
E)
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35) Aseptic means
A) free of all microbes.
B) clean.
C) free of pathogens.
D) sanitized.
E) sterile.
Answer: C
Explanation:

35)

A)
B)
C)
D)
E)

36) The process of incineration is used for
A) degerming.
B) sanitization.
C) disinfection.
D) sterilization.
E) both disinfection and sanitization.
Answer: D
Explanation:

36)

A)
B)
C)
D)
E)

37) Which of the following is an example of sanitization?
A) An autoclave is used to prepare nutrient agar.
B) A public toilet is treated with disinfectants.
C) A nurse prepares an injection site with an alcohol swab.
D) A surgeon washes her hands before surgery.
E) Heat is used to kill potential pathogens in apple juice.
Answer: B
Explanation:

A)
B)
C)
D)
E)

38) The dairy creamer used in restaurants is usually treated by
A) lyophilization.
B) autoclaving.
C) ultra-high-temperature pasteurization.
D) filtration.
E) ionizing radiation.
Answer: C
Explanation:

37)

A)
B)
C)
D)
E)

11

38)


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39) Which of the following procedures is currently the standard test used in the United States for
evaluating the efficiency of antiseptics and disinfectants?
A) use-dilution test
B) phenol coefficient
C) in-use test
D) microbial death rate
E) thermal death point
Answer: A
Explanation:

A)
B)
C)
D)
E)

40) Which of the following is the most appropriate pairing of microbe and biosafety level?
A) tuberculosis, BSL-1
B) E. coli, BSL-3
C) methicillin-resistant Staphylococcus aureus (MRSA), BSL-2
D) anthrax, BSL-1
E) Ebola, BSL-2
Answer: C
Explanation:

41)

A)
B)
C)
D)
E)

42) Disinfectants that damage membranes include
A) phenolics.
B) hydrogen peroxide.
C) alcohol.
D) iodine.
E) both alcohol and phenolics.
Answer: E
Explanation:

40)

A)
B)

C)
D)
E)

41) Which of the following is bacteriostatic?
A) flash Pasteurization
B) filtration
C) heating in an oven at 171°C for an hour
D) autoclaving
E) freezing below 0°C
Answer: E
Explanation:

39)

42)

A)
B)
C)
D)
E)
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43) Hydrogen peroxide is a(n)
A) sterilizing agent.
B) disinfecting and sterilizing agent.
C) disinfecting agent.

D) ineffective method of disinfecting.
E) antiseptic.
Answer: B
Explanation:

43)

A)
B)
C)
D)
E)

44) Seventy percent alcohol is effective against
A) prions.
B) protozoan cysts.
C) enveloped viruses.
D) bacterial endospores.
E) nonenveloped viruses.
Answer: C
Explanation:

44)

A)
B)
C)
D)
E)

45) Which of the following is NOT a desirable characteristic of an ideal antimicrobial agent?
A) It only arrests growth of vegetative cells.
B) It is stable during storage.
C) It acts quickly.
D) It is harmless to humans.
E) It is inexpensive.
Answer: A
Explanation:

45)

A)
B)
C)
D)
E)

SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
46) Microbial growth in jellies is inhibited by the (acidic/hypotonic/hypertonic) condition of
the food.

46)

Answer: hypertonic
Explanation:
47) Heavy metal and oxidizing agent disinfectants damage (proteins/DNA/membranes),
interfering with microbial metabolism.
Answer: proteins
Explanation:

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48) The process of freeze-drying microbes to preserve them is (lyophilization/dessication).

48)

Answer: lyophilization
Explanation:
49) Ultraviolet light penetrates (more/less) effectively than gamma rays.

49)

Answer: less
Explanation:
50) Disinfectants known as (alcohols/oxidizers/aldehydes) have the chemical group -CHO,
which reacts with and damages both proteins and nucleic acids.

50)

Answer: aldehydes
Explanation:
51)

51)

The antimicrobial chemical pictured above is a(n) (phenolic/surfactant/enzyme)

compound found in many consumer products.

Answer: phenolic
Explanation:
52) Natural antiseptics such as pine or clove oil are examples of antimicrobial compounds
called (alcohols/phenolics/detergents).

52)

Answer: phenolics
Explanation:
53) Elements such as iodine, chlorine, and bromine are examples of
(oxidizers/halogens/metals), which are the basis for many effective antimicrobial agents.

53)

Answer: halogens
Explanation:
54) A(n) (iodophor/halogen) is an iodine-containing organic compound found in such
antiseptics as Betadine.

54)

Answer: iodophor
Explanation:
55) The effectiveness of sterilization procedures is evaluated using (prions/cysts/endospores)
because of their resilience.

55)

Answer: endospores
Explanation:
56) The deadliest, most contagious microbes are studied under conditions of
(BSL-4/BSL-3/BSL-2/BSL-1) containment.
Answer: BSL-4
Explanation:

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57) The lowest temperature that kills all cells in a broth in 10 minutes is known as the
(microbial/thermal) death point.

57)

Answer: thermal
Explanation:
58) The amount of time needed to sterilize materials using moist heat is (more/less) than the
time needed to sterilize using dry heat.

58)

Answer: less
Explanation:
59) The process of heating milk or fruit juice to levels that kill any pathogenic microbes present
is known as (pasteurization/sanitization/lyophilization).

59)

Answer: pasteurization
Explanation:
60) The (endospores/cysts/prions) are the infectious agents most resistant to antimicrobial
agents or processes.

60)

Answer: prions
Explanation:
TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false.
61) Removal of microbes from the skin is antisepsis.
Answer:
True
Explanation:

61)

False

62) Some viruses are inactivated by the same chemical or physical agents that damage cytoplasmic
membranes.
Answer:
True
Explanation:

False

63) The phenol coefficient is one of the most widely used measurements of an antimicrobial agent's

effectiveness.
Answer:
True
Explanation:

64)

False

65) The pH conditions under which a chemical disinfectant is used do not alter its efficacy.
Answer:
True
Explanation:

65)

False

66) No chemical or antimicrobial agents inactivate prions.
Answer:
True
Explanation:

63)

False

64) Refrigeration is an effective germicidal method.
Answer:
True

Explanation:

62)

False

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67) By themselves, soaps have only degerming activity, not antimicrobial activity.
Answer:
True
Explanation:

False

68) Antimicrobial agents usually work best at high temperatures and high pH levels.
Answer:
True
Explanation:

69)

False

70) The decimal reduction time is the time required to kill all the microbes in a given sample.
Answer:

True
Explanation:

68)

False

69) Slow freezing is more damaging to microbial cells than quick freezing.
Answer:
True
Explanation:

67)

70)

False

ESSAY. Write your answer in the space provided or on a separate sheet of paper.
71) A student is shopping for antibacterial hand cleansers and is trying to decide which one to buy. One is a
"waterless" hand gel containing 70% isopropanol, the second is an "antibacterial" hand soap containing triclosan
(a phenolic), and the third is a wipe that lists benzethonium chloride (a synthetic quaternary ammonium salt) as
the active ingredient. Compare and contrast these cleansers in terms of the action of the antimicrobial ingredient
and the level of disinfection (degerming, germistatic, germicidal).
Answer: All three are germicidal, although not all to the same degree. The alcohol of the waterless hand cleaner is
a germicide that disrupts cytoplasmic membranes and denatures proteins. It is not effective against
bacterial endospores or fungal spores, and it has limited effect on nonenveloped viruses. The alcohol
evaporates quickly, so the germicidal effect is short term. The waterless hand cleaner is an
intermediate-level disinfectant and is not an effective degermer. The hand soap contains a phenolic,
which also damages cytoplasmic membranes and denatures proteins, and is effective on the same range

of microbes as the alcohol. Phenolics are intermediate-level disinfectants that persist on surfaces for long
periods of time, providing extended disinfection. If used with running water and the hands are
vigorously rubbed, the hand soap can be an effective degermer. Synthetic "quats" (quaternary
ammonium compounds) disrupt cell membranes. They are effective against fungi, enveloped viruses,
and most bacteria, but not against nonenveloped viruses, nor on endospores. Quats are low-level
disinfectants that are germicidal for some microbes. The action of using and discarding the wipe provides
some degerming effect.
72) What is the in-use test, and why is it more useful than other methods of evaluating disinfectants?
Answer: The in-use test is a method of evaluating antimicrobial agents such as disinfectants or antiseptics. It
involves collecting specimens from objects that need to be disinfected, both before and after the
disinfecting agent is applied. Then the specimens are inoculated into growth media, and the presence or
absence of growth is an indicator of the effectiveness of the agent. The in-use test is regarded as an
informative and useful test because it makes use of microbes that are actually found in the area of
concern, and it gives a "real-life" picture of how the antimicrobial agent will work in that situation.
Conversely, other tests, such as the disk-diffusion test or the use-dilution test, are not as useful because
they rely on standardized conditions in a laboratory environment, and using test microbes that may or
may not have any relation to the actual microbes that need to be targeted by the antimicrobial agent.
Additionally, in some environments, many microbes form biofilms that can affect the activity of an
antimicrobial agent, and these biofilms are not normally present in standardized testing procedures.
Therefore, although the in-use test is not as convenient or quick as the other types of tests, it is regarded
as more useful.

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73) Compare and contrast the nine major types of antimicrobial chemicals in terms of their effective on microbes.

Answer: Alcohols disrupt lipid membranes and denature proteins, are effective bactericidal, fungicidal agents,
and inactivate enveloped viruses. They are effective in the range of 70 - 90% concentration and the effect

is temporary due to evaporation. Aldehydes are highly effective germicidals that permanently damage
DNA and proteins and gluteraldehyde can sterilize with long exposure. Enzymes can be effective at
destroying microbes, but tend to be limited in their effect to specific classes of microbes. For example,
lysozyme is effective against bacteria, primarily Gram-positive bacteria. Gases like ethylene oxide are
highly effective germicidals that are also highly toxic to humans and are therefore only used under
highly controlled conditions. Halogens (iodine, chlorine, fluorine and bromine) are moderate level
disinfectants that disrupt the structure of proteins, particularly enzymes, and thereby arrest metabolic
activity. Heavy metals are low level bacteriostatic and fungistatic agents that disrupt the activity of
proteins, slowing metabolic activity. Oxidizing agents are high level antimicrobials that denature
proteins and arrest metabolic activity. Phenolics are effective antimicrobials that damage proteins and
disrupt lipid membranes, and are long lasting. Surfactants range in effectiveness from low level
microbistatic soaps to more effective synthetic detergents like the quaternary ammonium compounds,
which are microbicidal, disrupting cytoplasmic membranes.
74) Design an experiment to compare the effectiveness of a physical and a chemical method of disinfection.
Answer: Answers will vary. Appropriate controls and methods should be included. An example is comparison of
filtration and chlorine bleach.
Prepare a culture of bacteria of known cell concentration. Divide into three samples. Sample # 1 is the
positive control. Sample # 2 is filtered using a specified pore size filter (0.45 micron maximum pore size)
and the filtrate collected into a sterile container. Chlorine bleach is added to Sample #3 following
manufacturer's directions for dilution. The three samples are incubate, then the turbidity of each is
measured to determine if growth is evident in the two treated samples compared to the untreated
sample.
75) Some sterilization procedures do not kill all the microbes that may be present. Explain how these procedures
may for practical purposes still be considered sterilization.
Answer: Theoretically, sterilization is the complete removal or destruction of all microbes in a particular
environment. These include dormant forms of microbes, such as bacterial endospores. However, from a
practical standpoint, one must take other factors into account when deciding what is or is not sterile. For
example, the particular application of the sterilized material must be considered. Although there may be
hyperthermophilic microbes present in canned foods after sterilization, they cannot grow and divide at
normal shelf temperatures; thus, their presence does not cause problems. In practice, only those microbes

that would cause problems either by their presence or by their continued growth and reproduction are
generally the targets of sterilization methods. When these microbes have been eliminated, the goal of
sterilization can be said to have been reached.

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Answer Key
Testname: C9

1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)

19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
31)
32)
33)
34)
35)
36)
37)
38)
39)
40)
41)
42)
43)
44)
45)
46)
47)
48)

49)
50)

E
A
A
A
C
B
B
A
A
D
A
B
B
E
D
C
B
E
E
E
D
D
B
E
C
D
A

B
D
D
B
D
B
C
C
D
B
C
A
C
E
E
B
C
A
hypertonic
proteins
lyophilization
less
aldehydes
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Answer Key
Testname: C9

51)
52)
53)
54)
55)
56)
57)
58)
59)
60)
61)
62)
63)
64)
65)
66)
67)
68)
69)
70)
71)

phenolic
phenolics
halogens
iodophor
endospores
BSL-4
thermal

less
pasteurization
prions
TRUE
TRUE
FALSE
FALSE
FALSE
FALSE
TRUE
FALSE
TRUE
FALSE
All three are germicidal, although not all to the same degree. The alcohol of the waterless hand cleaner is a germicide
that disrupts cytoplasmic membranes and denatures proteins. It is not effective against bacterial endospores or fungal
spores, and it has limited effect on nonenveloped viruses. The alcohol evaporates quickly, so the germicidal effect is
short term. The waterless hand cleaner is an intermediate-level disinfectant and is not an effective degermer. The hand
soap contains a phenolic, which also damages cytoplasmic membranes and denatures proteins, and is effective on the
same range of microbes as the alcohol. Phenolics are intermediate-level disinfectants that persist on surfaces for long
periods of time, providing extended disinfection. If used with running water and the hands are vigorously rubbed, the
hand soap can be an effective degermer. Synthetic "quats" (quaternary ammonium compounds) disrupt cell
membranes. They are effective against fungi, enveloped viruses, and most bacteria, but not against nonenveloped
viruses, nor on endospores. Quats are low-level disinfectants that are germicidal for some microbes. The action of
using and discarding the wipe provides some degerming effect.
72) The in-use test is a method of evaluating antimicrobial agents such as disinfectants or antiseptics. It involves collecting
specimens from objects that need to be disinfected, both before and after the disinfecting agent is applied. Then the
specimens are inoculated into growth media, and the presence or absence of growth is an indicator of the effectiveness
of the agent. The in-use test is regarded as an informative and useful test because it makes use of microbes that are
actually found in the area of concern, and it gives a "real-life" picture of how the antimicrobial agent will work in that
situation. Conversely, other tests, such as the disk-diffusion test or the use-dilution test, are not as useful because they

rely on standardized conditions in a laboratory environment, and using test microbes that may or may not have any
relation to the actual microbes that need to be targeted by the antimicrobial agent. Additionally, in some environments,
many microbes form biofilms that can affect the activity of an antimicrobial agent, and these biofilms are not normally
present in standardized testing procedures. Therefore, although the in-use test is not as convenient or quick as the
other types of tests, it is regarded as more useful.

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full file at

Answer Key
Testname: C9

73) Alcohols disrupt lipid membranes and denature proteins, are effective bactericidal, fungicidal agents, and inactivate
enveloped viruses. They are effective in the range of 70 - 90% concentration and the effect is temporary due to
evaporation. Aldehydes are highly effective germicidals that permanently damage DNA and proteins and
gluteraldehyde can sterilize with long exposure. Enzymes can be effective at destroying microbes, but tend to be
limited in their effect to specific classes of microbes. For example, lysozyme is effective against bacteria, primarily
Gram-positive bacteria. Gases like ethylene oxide are highly effective germicidals that are also highly toxic to humans
and are therefore only used under highly controlled conditions. Halogens (iodine, chlorine, fluorine and bromine) are
moderate level disinfectants that disrupt the structure of proteins, particularly enzymes, and thereby arrest metabolic
activity. Heavy metals are low level bacteriostatic and fungistatic agents that disrupt the activity of proteins, slowing
metabolic activity. Oxidizing agents are high level antimicrobials that denature proteins and arrest metabolic activity.
Phenolics are effective antimicrobials that damage proteins and disrupt lipid membranes, and are long lasting.
Surfactants range in effectiveness from low level microbistatic soaps to more effective synthetic detergents like the
quaternary ammonium compounds, which are microbicidal, disrupting cytoplasmic membranes.
74) Answers will vary. Appropriate controls and methods should be included. An example is comparison of filtration and
chlorine bleach.
Prepare a culture of bacteria of known cell concentration. Divide into three samples. Sample # 1 is the positive control.

Sample # 2 is filtered using a specified pore size filter (0.45 micron maximum pore size) and the filtrate collected into a
sterile container. Chlorine bleach is added to Sample #3 following manufacturer's directions for dilution. The three
samples are incubate, then the turbidity of each is measured to determine if growth is evident in the two treated
samples compared to the untreated sample.
75) Theoretically, sterilization is the complete removal or destruction of all microbes in a particular environment. These
include dormant forms of microbes, such as bacterial endospores. However, from a practical standpoint, one must take
other factors into account when deciding what is or is not sterile. For example, the particular application of the
sterilized material must be considered. Although there may be hyperthermophilic microbes present in canned foods
after sterilization, they cannot grow and divide at normal shelf temperatures; thus, their presence does not cause
problems. In practice, only those microbes that would cause problems either by their presence or by their continued
growth and reproduction are generally the targets of sterilization methods. When these microbes have been
eliminated, the goal of sterilization can be said to have been reached.

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