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MICROBIOLOGY Midterm#1 > CH. 7: The Control of Microbial Growth > Flashcards

CH. 7: The Control of Microbial Growth Flashcards

1
Q

ignaz semmelweis/joseph lister

A

first efforts on microbial control (~100 years ago)

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2
Q

methods of control (2)

A

physical

chemical

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3
Q

sepsis:

A

refers to microbial contamination

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4
Q

asepsis:

A

the absence of significant contamination

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5
Q

sterilization:

A

removing ALL microbial life

via heating and filtration

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6
Q

sterilant:

A

sterilizing agent

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7
Q

commercial sterilization (and procedure):

A

killing C. botulinum endospores (via heating)

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8
Q

disinfection:

A

removing/destroying pathogens (vegetative cells, NOT endospores)

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9
Q

antisepsis:

A

removing pathogens from (disinfection of) LIVING TISSUE

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10
Q

degerming:

A

removing microbes from a limited area

  • *mechanical removal**
    e. g. alcohol swabs
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11
Q

sanitization:

A

lowering microbial counts to levels safe for public health and to minimize disease transmission

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12
Q

biocide/germicide:

A

killing microbes (NOT endospores)

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13
Q

bacteriostasis:

A

INHIBITING, not killing, microbes

i.e. stops growth temporarily

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14
Q

rate of microbial death?

A

bacterial populations tend to die at a constant rate

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15
Q

effectiveness of antimicrobial treatment depends on:

A
  1. number of microbes
  2. environment
  3. time of exposure
  4. microbial characteristics
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16
Q

[# of microbes] larger populations…

A

take longer to eliminate

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17
Q

[environment] organic matter…

A

inhibits antimicrobial chemicals

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18
Q

[environment] temperature:

A

disinfectants work better in warmer environments

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19
Q

[environment]

A

biofilms
fat/proteins protect microbes when heat treated
acidic conditions are favourable for disinfectants

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20
Q

[time of exposure]

A

extended exposure time is more effective against resistant microbes or endospores

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21
Q

[microbial characteristics] gram positive…

A

gram + bacteria more susceptible than gram negative (due to lipopolysaccharide in gram negative cell wall)

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22
Q

actions of microbial control agents (3)

A
  1. alteration of membrane permeability
  2. damage to proteins
  3. damage to nucleic acids
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23
Q

[actions of microbial control agents]

alteration of membrane permeability

A

–> target phospholipids and proteins to cause leaks in plasma membrane

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24
Q

[actions of microbial control agents]

damage to proteins

A

–> heat and chemicals can denature enzymes (hydrogen bonds are more easily destroyed than covalent bonds)

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25
Q

[actions of microbial control agents]

damage to nucleic acids

A
  • -> heat, chemicals, radiation can damage DNA/RNA thus interfering with vital functions (replications, metabolic enzymes)
  • -> often lethal to microbial cells
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26
Q

Heat

A
  • used to sterilize (lab media, glassware, hospital instruments, preserve canned food)
    • DENATURES & INACTIVATE PROTEINS
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27
Q

resistance of microbes to heat treatment is assessed by:

A

thermal death point (TDP) and thermal death time (TDT) (these give an idea of severity of treatment to kill a population of bacteria)

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28
Q

thermal death point (TDP):

A

lowest temperature at which cells in a culture are killed IN TEN MINUTES.

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29
Q

thermal death time (TDT):

A

minimal time during which ALL CELLS in a culture are killed at a given temperature.

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30
Q

decimal reduction time (DRT):

A

minutes required to kill 90% of a population at a given temperature

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31
Q

moist heat sterilization

A

DENATURES proteins
boiling for 10 mins = kills vegetative forms of bacteria, fungi, and their spores, and most viruses
(not perfect for sterilization - some viruses, endospres can resist boiling for a long time)

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32
Q

(moist heat sterilization) autoclave

A

steam under pressure

@ 15 psi & 121C: all organisms AND endospores in contact will die within 15 minutes

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33
Q

steam sterilization, steam must…

A

contact item’s surface

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34
Q

pasteurization

A

reduces spoilage organisms and pathogens

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35
Q

equivalent tx to pasteurization

A

30 mins at 63C

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36
Q

high-temperature short-time pasteurization:

A

72C for 15 seconds for milk

    • thermoduric organisms survive
  • unlikely to cause disease
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37
Q

ultra-high-temperature sterilization:

A

140C for <1 sec for milk

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38
Q

dry heat sterilization

A

kills by OXIDATION

    • dry heat
    • flaming
    • incineration
    • hot-air sterilization = longer time than moist heat because it takes longer for heat in air to be transferred to a cold body (ie. hot air needs 170C for 2 HRS; autoclave needs 121C for 15 mins)
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39
Q

filtration

A
    • used for heat sensitive materials

- - passage of liquid or air through a screen-like material with pores small enough to catch intended target

40
Q

HEPA filter removes microbes

A

> 0.3 um

41
Q

Membrane filtration removes microbes

A

> 0.22 um

42
Q

physical methods of microbial control (3)

A

lower temperature/quick freezing
high pressure
dessication
osmotic pressure

43
Q

[physical control] low temperature

A

inhibits microbial growth

    • refigeration is generally bacteriostatic
    • deep-freezing
    • quick freezing will usually make bacteria dormant (a slow thaw will do more damage)
44
Q

[physical control] high pressure

A

denatures proteins and carbohydrates

– preserves flavours, colours, and nutrients

45
Q

[physical control] dessication

A

prevents metabolism but DOES NOT KILL immediately

    • lyophilization (freeze-drying)
    • no effect on endospores or viruses
46
Q

[physical control] osmotic pressure causes..

A

plasmolysis

– NOT effective against moles

47
Q

radiation effect depends on (3)

A

wavelength
intensity
duration

48
Q

ionizing radiation mechanism

A

ionizes water to release OH hydroxyl (funny little dot thing)
damages DNA

49
Q

ionizing radiation examples

A

x-rays, gamma rays, electron beams

50
Q

nonionizing radiation mechanism

A

damages DNA

51
Q

nonionizing radiation example

A

UV, 260 nm

52
Q

microwaves kill by

A

heat; not especially antimicrobial

53
Q

ionizing radiation

A

have shorter wavelength - usually <1nm

have more energy

54
Q

ionizing radiation used in sterilization of

A

pharmaceuticals
disposable dental and medical supplies – plastic syringes, gloves, suturing materials, catheters
some foods (low-level ionizing radiation)

55
Q

ionizing radiation target theory of damage

A
    • passage of radiation through cellular structures = called a hit
    • one or few hits cause nonlethal mutations
    • many hits are likely to cause sufficient deleterious mutations
56
Q

nonionizing radiation

A

longer wavelength (e.g. UV)

  • damages DNA by formation of covalent bonds between adjacent pyrimidines, usually thymines (forms thymine dimers)
  • thymine dimers interfere with DNA replication
  • most effective wavelength for killing bacteria is 260 nm
  • UV lamps used in hospital rooms, nurseries, operating rooms, cafeteria
  • used to disinfect vaccines and certain medical products
  • UV not very penetrating, so organism must be directly exposed to it
  • disadvantage: can damage our eyes, cause burns and skin cancer
  • UV from sun has shorter damaging wavelength but it’s filtered by ozone layer
  • microbial pigments may also protect from sun
57
Q

chemical methods of microbial control

A

few achieve sterility
– most reduce populations to safe levels or remove vegetative vells of pathogens
no one single disinfectant is appropriate for all situations

58
Q

5 principles of effective disinfection

A
  1. concentration of disinfectant
  2. organic matter
  3. pH
  4. ability of disinfectant to contact microbe
  5. time
59
Q

two methods for testing disinfectant effectiveness

A
  1. use-dilution test (recommended)

2. disk-diffusion method (used in teaching labs)

60
Q

use-dilution test

A
  • metal cylinders dipped in test bacteria then dried
  • dried cultures are placed in disinfectant for 10 min at 20C
  • cylinders are transferred to culture media to determine whether bacteria survived treatment
61
Q

phenol and penolics

A

disrupt plasma membranes

  • remain active on surfaces for longer periods and when in contact with organics
  • effective on Mycobacterium tuberculosis
  • suitable for pus, saliva and feces
62
Q

phenol

A
  • first used by Lister
  • was effective at controlling sewage odour
  • > 1% concentration has significant antimicrobial effects
63
Q

phenolics

A

less irritating or increased activity

64
Q

bisphenols

A

also disrupt plasma membranes

65
Q

(bisphenol) hexachlorophene

A
  • used in hospitals (surgeries, nurseries)

- prescription lotion

66
Q

(bisphenol) triclosan

A
  • soaps
  • toothpaste
  • incorporated into kitchen equipment (knife handles, cutting boards)
  • resistance is being reported
  • inhibits an enzyme affecting lipid synthesis
67
Q

biguanides mechanism

A

primarily disrupt plasma membranes

68
Q

(bisguanides) chlorhexidine

A
  • used on skin and mucous membranes

- in alcohol or detergent solution, can be used for surgical hand scrubs and pre-op skin preparation

69
Q

(bisguanides) alexidine

A
  • more rapid
70
Q

(halogen) iodine

A
  • very effective: works against all bacteria, many endospores, some fungi and viruses
  • alter protein synthesis and membranes by complexing amino acids and unsaturated fatty acids
71
Q

(iodine) Tinctures

A

in aqueous alcohol

72
Q

(iodine) Iodophores

A

in organic molecules, e.g. Betadine

73
Q

(halogen) chlorine

A
  • hyochlorous acid (HOCl) formed with water
    CHLORAMINE: chlorine + ammonia
    –> is less effective than hypochlorite but long-lasting
  • oxidizing agents, prevents enzymes from functioning
  • effective against cysts and endospores at higher concentrations
  • widely used (municipal systems, swimming pools, surface disinfectant)
74
Q

alcohols

A
  • kills bacteria and fungi, enveloped viruses
  • ethanol (70% is optimal), isopropanol (denature proteins, dissolve lipids, requires water)
  • not really useful as an antiseptic
  • enhance effects of other chemical agents
75
Q

metals and what kind of action?

A
  • Ag, Hg, Cu, and Zn

- have Oligodynamic action (denatures proteins)

76
Q

silver sulfadiazine used

A

as a topical cream on burns

77
Q

copper compounds used

A

as either an algicide or antifungal agent

78
Q

Hg used

A

as an antifungal agent in paints

79
Q

Zn is used

A

as an antimicrobial put into some construction materials, mouthwashes, and antidandruff shampoos

80
Q

[surfactants/surface-active agents]

soap:

A

mechanical (emulsification)

degerming

81
Q

[surfactants/surface-active agents]

acid-anionic detergents:

A
  • anion reacts with plasma membrane

- sanitizing and nontoxic

82
Q

[surfactants/surface-active agents]

quaternary ammonium compounds (cationic detergents):

A
  • denature proteins, disrupt plasma membrane

- bactericidal, virucidal (enveloped viruses), fungicidal, amebicidal

83
Q

[chemical food preservatives]

organic acids and their salts:

A
  • inhibit metabolism
  • sorbic acid, sodium benzoate, calcium proprionate
  • -> control molds and bacteria in foods and cosmetics
84
Q

[chemical food preservatives]

nitrate (from NaNO3 and NaNO2) prevents..:

A

endospore germination in meats (controls botulism)

85
Q

[chemical food preservatives]

antibiotics in food

A

Nisin and natamycin prevent spoilage of cheese

86
Q

aldehydes

A
  • very effective
  • inactivate proteins by covalent cross-linking with functional groups (-NH2, -OH, -COOH, -SH)
  • Glutaraldehyde and ortho-phthalaldehyde (use: medical equipment)
  • formaldehyde gas
87
Q

gaseous sterilants

A
  • used in a closed chamber
  • cross-linking of nucleic acids and proteins
  • use: heat-sensitive material (ethylene oxide)
88
Q

plasma

A
  • gas excited by electromagnetic field
  • free radicals destroy microbes, even endospores
  • use: tubular instruments (e.g. scopes)
89
Q

supercritical fluids

A
  • compressed CO2 with gaseous and liquid properties

- use: medical implants and food

90
Q

peroxygens

A
  • oxidizing agents

- use: contaminated surfaces (O3, H2O2, peracetic acid, benzoyl peroxide)

91
Q

[peroxygens] gaseous hydrogen peroxide (H2O2) use

A

sterilize hospital rooms

92
Q

[peroxygens] peracetic acid use

A

powerful sterilant and leaves no toxic residues, just water and acetic acid, and can be used on food

93
Q

[peroxygens] ozone (O3) use

A

supplements chlorine, too reactive to use on its own

94
Q

order of microorganisms from most resistant to least resistant to CHEMICAL biocides:

A 
Prions
Endospores of bacteria
Mycobacteria
Cysts of protozoa
Vegetative protozoa
Gram-negative bacteria
Fungi, including most fungal spores
Viruses without envelopes
Gram-positive bacteria
Viruses with lipid envelopes
95
Q

_____ (chemical antimicrobial) is most effective against endospores and mycobacteria

A

Glutaraldehyde

MICROBIOLOGY Midterm#1 (4 decks)

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