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Microbiology > Ch 7: Control of Microbial Growth > Flashcards

Ch 7: Control of Microbial Growth Flashcards

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1
Q

What is the difference between disinfection and antisepsis?

A

Disinfection: treatment used to kill or inhibit microorganisms on inanimate objections

Antisepsis: treatment used to kill or inhibit organisms on living tissue

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2
Q

What is degerming?

A

Removing microbes from a limited area

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3
Q

What is sanitization?

A

Lower microbial counts on eating utensils

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4
Q

What is sepsis?

A

Presence of a toxin or pathogenic organism in blood and tissue

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5
Q

What is Asepsis?

A

Absence of contamination by unwanted bacteria

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6
Q

What factors influence the effectiveness of antimicrobial treatments?

A
  1. Number of microbes
  2. environmental influences
  3. time of exposure
  4. Microbial characterists
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7
Q

What type of environmental influences can influence the effectiveness of antimicrobial treatments?

A
  1. Presence of organic matter that protects from antimicrobials (i.e. biofilm)
  2. Suspensions rich in fats and proteins that protect from heat
  3. Temperature
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8
Q

What is the thermal death point (TDP) of a microbe?

A

THe lowest temperature at which all the microbes in a liquid culture will be killed in 10 minutes

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9
Q

What is the thermal death time (TDT) of a microbe?

A

The length of time required to kill all microbes in a liquid culture at a given temperature

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10
Q

What is the decimal reduction time (DRT or D value) of a microbe?

A

The length of time required to kill 90% of a bacterial population at a given temperature

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11
Q

How effective is boiling at killing microbes?

A

100 ℃ kills all vegetative bacterial pathogens, fungi and their spores, and most viruses within 10 minutes

EXCEPT ENDOSPORES

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12
Q

How does autoclaving work?

A

Sterilization by steam under pressure of about 15 psi (121 ℃)

Kill all organisms and endospores in about 15 minutes

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13
Q

What is pasteurization?

A

Eliminates pathogens and reduces food spoilage organisms without alter flavor of food

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14
Q

What is Vat pasteurization?

A

Pasteur’s original method

Heat 63 ℃ for 30 minutes

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15
Q

How is milk most commonly pasteurized today?

A

High-temperature short-time (HTST)

72 ℃ for 15 seconds

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16
Q

Why do pasteurization times and temperatures vary for different food products?

A
  1. Heat is less efficient in viscous foods
  2. Fats in foods are protective against heat
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17
Q

How does the dairy industry routinely measure the effectiveness of pasteurization?

A

Phosphatase assay (normal milk enzyme denatured in pasteurization)

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18
Q

How is milk sterilized?

A

Ultra-high-temperature: 140 ℃ for 2-5 seconds

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19
Q

What are some dry heat sterilization methods?

A
  1. Hot-air sterilization
  2. Direct flaming to a red glow
  3. Incineration
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20
Q

How does membrane filtration work?

A

Liquid is passed through a membrane (cellulose acetate, nitrocellulose, etc.) to remove microbes >0.22 μm (some can filter 0.01 μm)

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21
Q

High-efficiency particulate air (HEPA) filter remove microbes _____

A

>0.3 μm

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22
Q

In what situation is filtration the only practical way to eliminate undesirable microbes?

A

If you have something you don’t want destroyed by the heat of an autoclave

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23
Q

Refrigeration (0-7 ℃) is _____ for most microbes aside from psychotrophs.

A

Bacteriostatic

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24
Q

Deep-freezing renders microorganisms _____

A

Dormant

Does not necessarily kill them

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25
Q

What very high pressure is applied to a liquid suspension to kill microbes? How does it compare to pressures in the deepest parts of the ocean?

A

87,000 psi for 3-5 mins

Ocean: 16,000 psi

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26
Q

What is desiccation?

A

Halting of metabolism by extreme dehydration, however it leaves cells viable for years

27
Q

How does ionizing radiation kill microbes? Examples?

A

Splits water into ROS that react with cell components (especially DNA)

Ex: X-rays, gamma rays, high energy electron beams

28
Q

How does nonionizing radiation kill microbes? What wavelength is most effective?

A

Induces thymine dimers

UV, 260 nm

29
Q

How do microwaves kill microbes?

A

Moisture heating

30
Q

What does this symbol indicate?

A

Food that has been irradiated

31
Q

Would a UV germicidal lamp be a good method for a post office to sterilize mail?

A

No. Can’t penetrate paper

32
Q

What type of radiation is used to sterilize disposable dental and medical supplies?

A

Gamma and high energy electron radiation

33
Q

What factors must be considered when disinfecting?

A
  1. Disinfectant concentration
  2. Contact with microbe (is scrubbing necessary?)
  3. Time
  4. Nature of disinfected medium (pH or presence of organic material)
34
Q

True or false. No single disinfectant is appropriate for all conditions.

A

True

35
Q

What is the Use-Dilution test?

A

The current standard for evaluating the effectiveness of disinfectants and antiseptics

Dried cultures are placed in the manufacturer’s recommended dilution of a disinfectant for 10 minutes at 20 ℃. Survival is demonstrated by turbidity (culture)

36
Q

What is the disk-diffusion method for evaluating the effectiveness of disinfectants and antiseptics?

A

A disk of filter paper is soaked with a chemical and placed on an inoculated agar plate, a clear zone of inhibition indicates effectiveness

37
Q

Why is phenol no longer used as a disinfectant?

A

Skin irritation and disagreeable odor

38
Q

What are phenolics? Examples?

A

Phenol derivatives designed to reduce irritating qualities and increase antimicrobial activity

Ex: O-phenylphenol (active ingredient in lysol)

39
Q

What are bisphenols?

A

Disinfectants that contain two phenolic groups covalently linked

40
Q

What is hexachlorophene?

A

Bisphenol used in prescription skin cleanser pHisoHex for acne, surgical soap, and nursery infections

41
Q

What is Triclosan?

A

Bisphenol that was until recently used as an antimicrobial in soap, mouth wash, toys, underwear, sponges, etc.

42
Q

What law is in place in regard to triclosan?

A

Cannot be in anything non-medical due to concerns that bacteria may develop a resistance to it

43
Q

How do phenols, phenolics, and bisphenols act as antimicrobials? What microbe is especially susceptible to them?

A

Disrupt plasma membrane

Mycobacteria most susceptible

44
Q

What are biguanides? Example?

A

Disinfectants synthesized from guanine that act on the cell membrane

Ex: chlorohexidine

45
Q

What are biguanides least effective against?

A

Nonenveloped viruses and spores

46
Q

What halogens can be used as disinfectants?

A

Iodine (I2) as betadine

Chlorine (Cl2) as hypochlorous acid or bleach

47
Q

How does alcohol work as a disinfectant?

A

Denaturing proteins and dissolving lipid bilayers

48
Q

What heavy metals can be used as disinfectants?

A

Silver

Mercury

Copper

Zinc

49
Q

How do heavy metals work as disinfectants?

A

Proteins are denatured when heavy metal ions combined with sulfhydryl (-SH) groups

50
Q

How do sodium benzoate and potassium sorbate function as food preservatives?

A

Bacteriostatic and fungistatic respectively in acid foods (cheese and soft drinks)

51
Q

How does calcium propionate function as a food preservative?

A

Preservative for bakery products. Active against bread molds and spores

52
Q

How does sulfur dioxide function as a food preservative?

A

Inhibit microbial growth in wine and dried fruit

53
Q

How do sodium nitrates and nitrites function as food preservatives?

A

Selectively inhibit iron-containing enzymes of C. botulinum in meats

54
Q

What antibiotics are used in food preservation? (2)

A

Natamycin: against molds and yeasts in cheeses

Nisin: against gram-positive organisms and spores in cheeses

55
Q

What organism produces natamycin?

A

bacterium Streptomyces natalensis

56
Q

What organism produces nisin?

A

Bacterium Lactococcus lactis

57
Q

What are the most effective chemical disinfectants?

A

Aldehydes

58
Q

How do aldehydes act as disinfectants?

A

Inactivate proteins by cross-linking with function groups:

  • NH2
  • OH
  • COOH
  • SH
59
Q

What are the 3 most effective aldehydes used for disinfection?

A
  1. formaldehyde
  2. Gluteraldehyde
  3. ortho-phthaladehyde
60
Q

What are the two most commonly used gaseous chemo-sterilants?

A

Ethylene oxide

Chlorine dioxide

61
Q

How does plasma sterilization work?

A

Hydrogen peroxide vapor is ionized by an electrochemical field to produce UV light and free radicals (ROS)

62
Q

Are gram-negative or gram-positive bacteria more resistant to disinfectants and antiseptics?

A

Gram-negative

63
Q

True or false. Mycobacteria, endospores, and protozoan cysts are susceptible to disinfectants and antiseptics.

A

False. They are very resistant

Microbiology (19 decks)

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