Download File - Microbiology

PowerPoint to accompany
Microbiology:
A Systems Approach
Cowan/Talaro
Chapter 11
Physical and Chemical
Control of Microbes
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 11
Topics
- Controlling Microorganisms
- Physical Control
- Chemical control
2
An overview of the microbial control methods.
Fig. 11.1 Microbial control methods
3
Controlling Microorganisms
•
•
•
•
Microbial agents
Sanitation
Effectiveness
Mode of action
4
Microbial agents
•
•
•
•
•
•
-static agents
-cidal agents
Resistance
Terms
Effectiveness
Mode of action
5
-static agents
• Temporarily prevent the growth of
microbes
– Bacteriostatic
– Fungistatic
6
-cidal
• Kill or destroy a microorganism
– Germicide
– Bactericide
7
Resistance
• Highest resistance - bacterial spores and
prions
• Moderate resistance - some bacteria,
protozoan cysts, fungal sexual spores, naked
viruses
• Least resistance - most bacteria, fungal
nonsexual spores and hyphae, enveloped
viruses, yeast, protozoan trophozoites
8
Comparing the resistance between endospores and vegetative
cells to control agents.
9
Table 11.1 Relative resistance of bacterial endospors and vegetative cells
Terms
•
•
•
•
•
Sterilization
Disinfection
Antisepsis
Sanitation
Degermination
10
Sterilization
• A process that destroys or removes all
viable microorganisms, including spores
and viruses
• Physical or chemical agents
• Inanimate objects
– Surgical instruments, commercially
packaged foods
11
Disinfection
• Use of physical process or chemical
agent (disinfectant) to destroy
vegetative pathogens.
• Removes toxins
• Won’t destroy bacterial endospores
12
Antisepsis
• Chemical agents (antiseptics) destroy or
inhibit vegetative pathogens
• Agent is used on skin and mucous
membranes
13
Sanitation
• Reducing the number of
microorganisms to a safe public health
standard
• Physical and chemical agents
• Dishwashers, sanitizers
14
Degermination
• On Human skin - reducing the number
of microorganisms by mechanical
means
– Wiping the microbes from the skin surface
• Physical and chemical agents can be
used
15
Factors that influence
Effectiveness
• Number of microorganisms
• Target population (bacteria, fungi,
spores, viruses)
• Temperature and pH
• Concentration of agent
• Mode of action
• Interfering agents present (solvents,
debris, saliva, blood, feces)
16
Factors that influence the effectiveness of antimicrobial agents.
Fig. 11.2 Factors that influence the rate at which microbes
are killed by antimicrobial agents
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Mode of action
How Antimicrobial Agents Work
• Targets
–
–
–
–
–
Cell wall
Cell membrane
Nucleic acid synthesis
Protein synthesis
Protein function
18
Target: Cell Wall
• Bacteria and fungi have cell walls
– Block synthesis of cell wall
– Degrade cellular components of cell wall
– Destroy or reduce stability of cell wall
• Agents
– Penicillin, detergents, alcohols
19
Target: Cell membrane
• All microbes have a cell membrane
• Enveloped viruses have an envelope (an
outer bilayer of phospholipids)
• Agents that destroy cell membranes bind
and penetrate lipids
– Membrane loses selective permeability
(leakage)
• Agents
– Surfactants
20
The effect of surfactants on the cell membrane.
Fig. 11.3 Mode of action of surfactants
21
Nucleic acid synthesis
• Some agents irreversibly bind to DNA
– Stop transcription and translation
– Can cause mutations
• Agents
– Chemical agent – formaldehyde
– Physical agent – radiation
22
Protein synthesis
• Agents that bind to ribosomes
– Stop translation
– Prevent peptide bonds
• Agent
– Chloramphenicol
• Remember: bacteria have 70S ribosomes; eukaryotes have 80S
ribosomes but have 70S ribosomes in the mitochondria
23
Protein function
•
•
•
•
Block protein active sites
Prevent binding to substrate
Denature protein
Agent
– Physical – Heat, pH change
– Chemical – alcohols, acids, phenolics,
metallic ions
24
The effects of heat, pH, and blocking agents on the function of
proteins.
Fig. 11.4 Modes of action affecting protein function
25
Physical Control
• Heat
• Radiation
• Filtration
26
HEAT
Mode of action
• Moist heat
– Coagulation of proteins
– Denaturation of proteins
• Dry heat
– Dehydration
– Denaturation
– Oxidation (burning to ashes)
• Thermal death time
27
Moist Heat Methods
• Boiling water
• Steam and pressure
• Pasteurization
28
Boiling water
• Boiling water at 100 ˚C for 30 minutes –
Decontaminates but doesn’t sterilize
• Kills most non-spore forming pathogens
• Won’t destroy endospores
• Examples: home sanitizing and
disinfecting, disinfecting unsafe water
29
Steam and pressure
• Increasing pressure above normal
atmospheric pressure will result in water
boiling temperatures above 100˚C
• 15 psi / 121˚C / 15-30 min.
• Effectively destroys spores
• Sterilizes inanimate objects (glassware)
– Material must be able to withstand both heat
and moisture
• Ex. Autoclave and home pressure cooker
30
A diagram of an autoclave.
31
Fig. 11.5 Steam sterilization with the autoclave
Pasteurization
• Disinfection of beverages
• Exposes beverages to 71.6 ˚C for 15 seconds
– Stops fermentation
• Prevents the transmission of milk-borne
diseases
– Salmonella, Campylobacter, Listeria,
Mycobacteria
• Examples: Milk industry, wineries, breweries
32
Dry heat
• Hot air ( e.g., oven)
• Incineration
• Not as efficient as using moist heat
– Temperature and /or time of exposure is
greater than moist heat
33
Hot air
• Hot air
– Oven
– Effective at 150˚C to 180˚C for 2-4 hrs
– Effective for inanimate objects and oils
34
Incineration
• Destroys microbes to ashes or gas
– Flame - 1870˚C
– Furnace - 800˚C to 6500˚C
35
An infrared incinerator uses flame to burn or oxidize materials into
ashes.
Fig. 11.6 Dry heat incineration
36
Effects of cold and dessication
• Cold temperatures reduce the activity of
some microbes, not psychrophiles
– Not a disinfection or sterilization method
• Dessication or dehydration kill some
microorganisms
– Lyophilization – freezing and drying
method used to preserve microbes
37
Radiation
• Types of radiation
• Modes of action
• Applications
38
Types of radiation
• Ionizing – Very High Energy
– Gamma rays (Highest ionizing energy)
– X-rays (Intermediate ionizing energy)
– Cathode rays (least ionizing energy)
• Nonionizing
– Ultraviolet
39
Mode of actions
• Ionizing radiation ejects electrons from
an atom
– High energy
• Penetrates liquids and solids effectively
• Nonionizing radiation raises atoms to a
higher energy state
– Lower energy than ionizing
• Less penetration capability
• Pyrimidine dimers form in DNA
40
The effects of ionizing and nonionizing radiation on DNA.
41
Fig. 11.7 Cellular effects of irradiation
Ultraviolet (UV) radiation can cause the formation of pyrimidine
dimers on DNA.
Fig. 11.9 Formation of pyrimidine dimers by the action
of UV radiation.
42
Applications
• Ionizing radiation
– Alternative sterilization method
– Materials sensitive to heat or chemicals
– Some foods (fruits, vegetables, meats)
• Nonionizing radiation
– Alternative disinfectant
– Germicidal lamp in hospitals, schools, food
preparation areas (inanimate objects, air, water)
43
A gramma radiation machine (ionizing radiation) used to sterilize
fruits, vegetables, meats, fish, and spices.
Fig. 11.8 Sterilization with Ionizing Radiation
44
A UV treatment system can be used to disinfect water.
45
Fig. 11.10 A UV treatment system for disinfection of water
Filtration
• Removes microbes and spores from
liquids and air
• Perforated membrane
– Pore sizes vary
• Applications
– Liquids that are sensitive to heat
• Serum, vaccines, media
46
An example of a filtration system.
Fig. 11.11 Membrane filtration
47
Chemical control
• Widely used agents
• Applications
48
Example of chemical agents, their target microbe, level of activity,
and toxicity.
Table 11.5 Qualities of chemical agents used in health care
49
Applications
•
•
•
•
•
•
•
•
•
Halogens
Phenolics
Surfactants
Hydrogen peroxide
Detergents and soaps
Heavy metals
Aldehydes
Gases
Dyes, acids, and alkalis
50
Halogens
• Chlorine
– Disinfectant and antiseptic
• Disrupt sulfhydryl groups in amino acids
• Iodine
– Topical antiseptic
• Disruption is similar to chlorines
51
Phenolics
• Vary based on functional groups
attached to the aromatic ring
• Examples: Hexachlorophene, Triclorsan
– Microcidal
– Ingredient in soaps to kitty litter
• Disrupts cell walls and membranes,
52
Phenolics contain a basic phenolic aromatic ring with different
functional groups.
Fig. 11.12 Some phenolics
53
Alcohols
• Ethyl alcohol, isopropyl (rubbing alcohol)
– 70% concentration dissolve membrane
lipids, disrupt cell surface tension,
denatures proteins
• Germicidal and skin degerming
54
Hydrogen peroxide
• Colorless and caustic liquid
• Form hydroxyl free radicals
– Effective against anaerobes
• Skin and wound cleaner
• Quick method for sterilizing medical
equipment
55
Examples of different devices used to sterilize medical equipment.
Fig. 11.13 Sterile processing of invasive equipment
protects patients.
56
Detergents and soaps
• Quaternary ammonium – NH4 (quats)
– Cationic
– Bind and disrupt cell membrane
– Low-level disinfectant in the clinical setting
• Soaps
– Fatty acids, oils, sodium or potassium salts
– Cleaning agents
– More effective if mixed with germicides
57
For detergents, the positive charge region binds bacteria and the
uncharged region integrates into the cell membrane.
Fig. 11.14 The structure of detergents
58
Comparison between nongermicidal and germicidal soaps.
Fig. 11.15 Graph showing effects of handscrubbing
59
Heavy metals
• Mercury, silver,
– Inactivate proteins
– Preservatives in cosmetics and ophthalmic
solutions
60
Demonstration of the effects silver and gold have on microbial
growth.
Fig. 11.16 demonstration of the oligodynamic action
of heavy metals.
61
Aldehydes
• Glutaraldehyde
– Crosslink with proteins on the cell surface
– Disinfectant for surgical instruments
• Formaldehyde
– Formalin is used as a tissue preservative
62
Representation of the action of glutaraldehyde.
Fig. 11.17 Actions of glutaraldehyde
63
Gases
• Ethylene oxide
– Reacts with functional groups of DNA and
proteins
– Sterilizes and disinfects plastic materials
64
Examples of different devices that use gas to sterilize equipment.
Fig. 11.18 Sterilization using gas
65
Dyes
• Crystal violet
• Effective against Gram positive bacteria
• Ointments
66
Acids and alkalis
• Acetic acid
• Ammonium hydroxide
• Prevents spore germination and
vegetative growth
• Food preservative
67