More Related Content Similar to Ch 07_lecture_presentation (20) Ch 07_lecture_presentation1. Chapter 7
The Control of
Microbial Growth
© 2013 Pearson Education, Inc.
Copyright © 2013 Pearson Education, Inc.
Lectures prepared by Christine L. Case
Lectures prepared by Christine L. Case
3. The Terminology of Microbial Control
Learning Objective
7-1 Define the following key terms related to microbial
control: sterilization, disinfection, antisepsis,
degerming, sanitization, biocide, germicide,
bacteriostasis, and asepsis.
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4. The Terminology of Microbial Control
Sepsis refers to microbial contamination
Asepsis is the absence of significant contamination
Aseptic surgery techniques prevent microbial
contamination of wounds
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5. The Terminology of Microbial Control
Sterilization: removing all microbial life
Commercial sterilization: killing C. botulinum
endospores
Disinfection: removing pathogens
Antisepsis: removing pathogens from living tissue
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6. The Terminology of Microbial Control
Degerming: removing microbes from a limited area
Sanitization: lowering microbial counts on eating
utensils
Biocide/germicide: killing microbes
Bacteriostasis: inhibiting, not killing, microbes
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7. Check Your Understanding
The usual definition of sterilization is the removal or
destruction of all forms of microbial life; how could
there be practical exceptions to this simple
definition? 7-1
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8. The Rate of Microbial Death
Learning Objective
7-2 Describe the patterns of microbial death caused
by treatments with microbial control agents.
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10. Figure 7.1a Understanding the Microbial Death Curve.
One log decrease =
90% of population
killed
Arithmetic number of surviving cells
log10 of number of surviving cells
Plotting the typical microbial death curve
logarithmically (red line) results in a straight line.
Time (min)
(a) Plotting the typical microbial death curve arithmetically
(blue line) is impractical: at 3 minutes the population of
1000 cells would only be a hundredth of the graphed
distance between 100,000 and the baseline.
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11. Effectiveness of Treatment
Depends on:
Number of microbes
Environment (organic matter, temperature, biofilms)
Time of exposure
Microbial characteristics
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12. Figure 7.1b Understanding the Microbial Death Curve.
log10 of number of surviving cells
sterile surgical equipment
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Time (min)
(b) Logarithmic plotting (red) reveals that if the
rate of killing is the same, it will take longer to kill
all members of a larger population than a smaller
one, whether using heat or chemical treatments.
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13. Check Your Understanding
How is it possible that a solution containing a million
bacteria would take longer to sterilize than one
containing a half-million bacteria? 7-2
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14. Actions of Microbial Control Agents
Learning Objective
7-3 Describe the effects of microbial control agents
on cellular structures.
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15. Actions of Microbial Control Agents
Alteration of membrane permeability
Damage to proteins
Damage to nucleic acids
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16. Check Your Understanding
Would a chemical microbial control agent that
affects plasma membranes affect humans? 7-3
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17. Physical Methods of Microbial Control
Learning Objectives
7-4 Compare the effectiveness of moist heat (boiling,
autoclaving, pasteurization) and dry heat.
7-5 Describe how filtration, low temperatures, high
pressure, desiccation, and osmotic pressure
suppress microbial growth.
7-6 Explain how radiation kills cells.
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18. Heat
Thermal death point (TDP): lowest temperature at
which all cells in a culture are killed in 10 min
Thermal death time (TDT): time during which all
cells in a culture are killed
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19. Decimal Reduction Time (DRT)
Minutes to kill 90% of a population at a given
temperature
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20. Figure 7.10 A comparison of the effectiveness of various antiseptics.
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22. Figure 7.2 An autoclave.
Exhaust valve
(removes steam
after sterilization)
Steam to
chamber
Safety
valve
Pressure gauge
Operating valve
(controls steam from
jacket to chamber)
Steam
Door
Steam
chamber
Air
Perforated shelf
Steam jacket
Sediment
screen
Thermometer
Automatic ejector valve
Pressure regulator
(thermostatically controlled;
for steam supply
closes on contact with
pure steam when air is
To waste line exhausted)
Steam supply
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25. Pasteurization
Reduces spoilage organisms and pathogens
Equivalent treatments
63°C for 30 min
High-temperature short-time: 72°C for 15 sec
Ultra-high-temperature: 140°C for <1 sec
Thermoduric organisms survive
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26. Dry Heat Sterilization
Kills by oxidation
Dry heat
Flaming
Incineration
Hot-air sterilization
Hot-Air
Equivalent Treatments
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Autoclave
170˚C, 2 hr
121˚C, 15 min
27. Filtration
HEPA removes microbes >0.3 µm
Membrane filtration removes microbes >0.22 µm
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28. Figure 7.4 Filter sterilization with a disposable, presterilized plastic unit.
Flask of
sample
Cap
Membrane filter
Cotton plug in
vacuum line
ensures sterility
Sterile
filtrate
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Vacuum line
29. Physical Methods of Microbial Control
Low temperature inhibits microbial growth
Refrigeration
Deep-freezing
Lyophilization
High pressure denatures proteins
Desiccation prevents metabolism
Osmotic pressure causes plasmolysis
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30. Figure 7.5 The radiant energy spectrum.
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31. Radiation
Ionizing radiation (X rays, gamma rays, electron
beams)
Ionizes water to release OH•
Damages DNA
Nonionizing radiation (UV, 260 nm)
Damages DNA
Microwaves kill by heat; not especially antimicrobial
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32. Check Your Understanding
How is microbial growth in canned foods prevented?
7-4
Why would a can of pork take longer to sterilize at
a given temperature than a can of soup that also
contained pieces of pork? 7-5
What is the connection between the killing effect of
radiation and hydroxyl radical forms of oxygen? 7-6
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33. Chemical Methods of Microbial Control
Learning Objectives
7-7 List the factors related to effective disinfection.
7-8 Interpret the results of use-dilution tests and the
disk-diffusion method.
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34. Principles of Effective Disinfection
Concentration of disinfectant
Organic matter
pH
Time
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35. Use-Dilution Test
Metal rings dipped in test bacteria are dried
Dried cultures are placed in disinfectant for 10 min
at 20°C
Rings are transferred to culture media to determine
whether bacteria survived treatment
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36. Figure 7.6 Evaluation of disinfectants by the disk-diffusion method.
Zone of inhibition
Chlorine
O-phenylphenol
Hexachlorophene
Quat
Staphylococcus aureus
(gram-positive)
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Chlorine
O-phenylphenol
Hexachlorophene
Quat
Escherichia coli
(gram-negative)
Chlorine
O-phenylphenol
Hexachlorophene
Quat
Pseudomonas aeruginosa
(gram-negative)
38. Clinical Focus 7.1 Infection Following Steroid Injection
Undiluted
Disk-diffusion test of Zephiran against M. abscessus.
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1:10
39. Check Your Understanding
If you wanted to disinfect a surface contaminated by
vomit and a surface contaminated by a sneeze, why
would your choice of disinfectant make a difference?
7-7
Which is more likely to be used in a medical clinic
laboratory, a use-dilution test or a disk-diffusion
test? 7-8
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40. Chemical Methods of Microbial Control
Learning Objectives
7-9 Identify the methods of action and preferred uses
of chemical disinfectants.
7-10 Differentiate halogens used as antiseptics from
halogens used as disinfectants.
7-11 Identify the appropriate uses for surface-active
agents.
7-12 List the advantages of glutaraldehyde over other
chemical disinfectants.
7-13 Identify chemical sterilizers.
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42. Figure 7.7ab The structure of phenolics and bisphenols.
(a) Phenol
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(b) O-phenylphenol
44. Figure 7.7cd The structure of phenolics and bisphenols.
(c) Hexachlorophene (a bisphenol)
(d) Triclosan (a bisphenol)
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46. Halogens
Iodine
Tinctures: in aqueous alcohol
Iodophors: in organic molecules
Alter protein synthesis and membranes
Chlorine
Bleach: hypochlorous acid (HOCl)
Chloramine: chlorine + ammonia
Oxidizing agents
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48. Table 7.6 Biocidal Action of Various Concentrations of Ethanol in Aqueous Solution against
Streptococcus pyogenes
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49. Heavy Metals
Ag, Hg, and Cu
Silver nitrate may be used to prevent gonorrheal
ophthalmia neonatorum
Silver sulfadiazine used as a topical cream on burns
Copper sulfate is an algicide
Oligodynamic action
Denature proteins
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51. Figure 7.9 The ammonium ion and a quaternary ammonium compound, benzalkonium chloride
(Zephiran).
Ammonium ion
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Benzalkonium chloride
52. Surface-Active Agents, or Surfactants
Soap
Degerming
Acid-anionic detergents
Sanitizing
Quaternary ammonium
compounds
(cationic detergents)
Bactericidal, denature proteins,
disrupt plasma membrane
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53. Chemical Food Preservatives
Organic acids
Inhibit metabolism
Sorbic acid, benzoic acid, and calcium propionate
Control molds and bacteria in foods and cosmetics
Nitrite prevents endospore germination
Antibiotics
Nisin and natamycin prevent spoilage of cheese
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54. Aldehydes
Inactivate proteins by cross-linking with functional
groups (–NH2, –OH, –COOH, –SH)
Use: medical equipment
Glutaraldehyde, formaldehyde, and ortho-phthalaldehyde
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59. Check Your Understanding
Why is alcohol effective against some viruses and
not others? 7-9
Is Betadine an antiseptic or a disinfectant when it is
used on skin? 7-10
What characteristics make surface-active agents
attractive to the dairy industry? 7-11
What chemical disinfectants can be considered
sporicides? 7-12
What chemicals are used to sterilize? 7-13
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60. Microbial Characteristics and Microbial
Control
Learning Objective
7-14 Explain how the type of microbe affects the
control of microbial growth.
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61. Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides.
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62. Table 7.7 The Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria
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63. Check Your Understanding
The presence or absence of endospores has an
obvious effect on microbial control, but why are
gram-negative bacteria more resistant to chemical
biocides than gram-positive bacteria? 7-14
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