5.1.E: Control of Microbial Growth (Exercises)
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13.1: Controlling Microbial Growth
Inanimate items, such as doorknobs, toys, or towels, which may harbor microbes and aid in disease transmission, are called fomites. Two factors heavily influence the level of cleanliness required for a particular fomite and, hence, the protocol chosen to achieve this level. The first factor is the application for which the item will be used and the second factor is the level of resistance to antimicrobial treatment by potential pathogens.
Multiple Choice
Which of the following types of medical items requires sterilization?
- needles
- bed linens
- respiratory masks
- blood pressure cuffs
- Answer
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A
Which of the following is suitable for use on tissues for microbial control to prevent infection?
- disinfectant
- antiseptic
- sterilant
- water
- Answer
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B
Which biosafety level is appropriate for research with microbes or infectious agents that pose moderate risk to laboratory workers and the community, and are typically indigenous?
- BSL-1
- BSL-2
- BSL-3
- BSL-4
- Answer
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B
Which of the following best describes a microbial control protocol that inhibits the growth of molds and yeast?
- bacteriostatic
- fungicidal
- bactericidal
- fungistatic
- Answer
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D
The decimal reduction time refers to the amount of time it takes to which of the following?
- reduce a microbial population by 10%
- reduce a microbial population by 0.1%
- reduce a microbial population by 90%
- completely eliminate a microbial population
- Answer
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C
Fill in the Blank
A medical item that comes into contact with intact skin and does not penetrate sterile tissues or come into contact with mucous membranes is called a(n) ________ item.
- Answer
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noncritical
The goal of ________ ________ protocols is to rid canned produce of Clostridium botulinum endospores.
- Answer
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commercial sterilization
True/False
Sanitization leaves an object free of microbes.
- Answer
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False
Short Answer
What are some characteristics of microbes and infectious agents that would require handling in a BSL-3 laboratory?
What is the purpose of degerming? Does it completely eliminate microbes?
What are some factors that alter the effectiveness of a disinfectant?
Critical Thinking
When plotting microbial death curves, how might they look different for bactericidal versus bacteriostatic treatments?
What are the benefits of cleaning something to a level of cleanliness beyond what is required? What are some possible disadvantages of doing so?
13.2: Using Physical Methods to Control Microorganisms
For thousands of years, humans have used various physical methods of microbial control for food preservation. Common control methods include the application of high temperatures, radiation, filtration, and desiccation (drying), among others. Many of these methods nonspecifically kill cells by disrupting membranes, changing membrane permeability, or damaging proteins and nucleic acids by denaturation, degradation, or chemical modification.
Multiple Choice
Which of the following methods brings about cell lysis due to cavitation induced by rapid localized pressure changes?
- microwaving
- gamma irradiation
- ultraviolet radiation
- sonication
- Answer
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D
Which of the following terms is used to describe the time required to kill all of the microbes within a sample at a given temperature?
- D-value
- thermal death point
- thermal death time
- decimal reduction time
- Answer
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C
Which of the following microbial control methods does not actually kill microbes or inhibit their growth but instead removes them physically from samples?
- filtration
- desiccation
- lyophilization
- nonionizing radiation
- Answer
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A
Fill in the Blank
In an autoclave, the application of pressure to ________ is increased to allow the steam to achieve temperatures above the boiling point of water.
- Answer
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steam
True/False
Ionizing radiation can penetrate surfaces, but nonionizing radiation cannot.
- Answer
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True
Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols do.
- Answer
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False
Short Answer
What is the advantage of HTST pasteurization compared with sterilization? What is an advantage of UHT treatment?
How does the addition of salt or sugar help preserve food?
Which is more effective at killing microbes: autoclaving or freezing? Explain.
Critical Thinking
In 2001, endospores of Bacillus anthracis , the causative agent of anthrax, were sent to government officials and news agencies via the mail. In response, the US Postal Service began to irradiate mail with UV light. Was this an effective strategy? Why or why not?
13.3: Using Chemicals to Control Microorganisms
In addition to physical methods of microbial control, chemicals are also used to control microbial growth. A wide variety of chemicals can be used as disinfectants or antiseptics. This section describes the variety of chemicals used as disinfectants and antiseptics, including their mechanisms of action and common uses.
Multiple Choice
Which of the following refers to a disinfecting chemical dissolved in alcohol?
- iodophor
- tincture
- phenolic
- peroxygen
- Answer
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B
Which of the following peroxygens is widely used as a household disinfectant, is inexpensive, and breaks down into water and oxygen gas?
- hydrogen peroxide
- peracetic acid
- benzoyl peroxide
- ozone
- Answer
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A
Which of the following chemical food preservatives is used in the wine industry but may cause asthmatic reactions in some individuals?
- nitrites
- sulfites
- propionic acid
- benzoic acid
- Answer
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B
Bleach is an example of which group of chemicals used for disinfection?
- heavy metals
- halogens
- quats
- bisbiguanides
- Answer
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B
Which chemical disinfectant works by methylating enzymes and nucleic acids and is known for being toxic and carcinogenic?
- sorbic acid
- triclosan
- formaldehyde
- hexaclorophene
- Answer
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C
Fill in the Blank
Doorknobs and other surfaces in clinical settings are often coated with ________, ________, or ________ to prevent the transmission of microbes.
- Answer
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copper, nickel, zinc
True/False
Soaps are classified as disinfectants.
- Answer
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False
Mercury-based compounds have fallen out of favor for use as preservatives and antiseptics.
- Answer
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True
Short Answer
Which solution of ethyl alcohol is more effective at inhibiting microbial growth: a 70% solution or a 100% solution? Why?
When might a gas treatment be used to control microbial growth instead of autoclaving? What are some examples?
What is the advantage of using an iodophor rather than iodine or an iodine tincture?
Critical Thinking
Looking at Figure 13.3.11 and reviewing the functional groups in Figure 7.1.5 , which alkylating agent shown lacks an aldehyde group?
Do you think naturally produced antimicrobial products like nisin and natamycin should replace sorbic acid for food preservation? Why or why not?
Why is the use of skin disinfecting compounds required for surgical scrubbing and not for everyday handwashing?
13.4: Testing the Effectiveness of Antiseptics and Disinfectants
Several environmental conditions influence the potency of an antimicrobial agent and its effectiveness. For example, length of exposure is particularly important, with longer exposure increasing efficacy. Similarly, the concentration of the chemical agent is also important, with higher concentrations being more effective than lower ones. Temperature, pH, and other factors can also affect the potency of a disinfecting agent.
Multiple Choice
Which type of test is used to determine whether disinfectant solutions actively used in a clinical setting are being used correctly?
- disk-diffusion assay
- phenol coefficient test
- in-use test
- use-dilution test
- Answer
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C
The effectiveness of chemical disinfectants has historically been compared to that of which of the following?
- phenol
- ethyl alcohol
- bleach
- formaldehyde
- Answer
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A
Which of the following refers to a germicide that can kill vegetative cells and certain enveloped viruses but not endospores?
- high-level germicide
- intermediate-level germicide
- low-level germicide
- sterilant
- Answer
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C
Fill in the Blank
If a chemical disinfectant is more effective than phenol, then its phenol coefficient would be ________ than 1.0.
- Answer
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greater
If used for extended periods of time, ________ germicides may lead to sterility.
- Answer
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high-level
In the disk-diffusion assay, a large zone of inhibition around a disk to which a chemical disinfectant has been applied indicates ________ of the test microbe to the chemical disinfectant.
- Answer
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susceptibility or sensitivity
Short Answer
Why were chemical disinfectants once commonly compared with phenol?
Why is length of exposure to a chemical disinfectant important for its activity?
Critical Thinking
What are some advantages of use-dilution and in-use tests compared with the disk-diffusion assay?