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Transcript of Microbiology: A Systems Approach Chapter 11 Physical and Chemical Control of Microbes PowerPoint to...
![Page 1: Microbiology: A Systems Approach Chapter 11 Physical and Chemical Control of Microbes PowerPoint to accompany Cowan/Talaro Copyright The McGraw-Hill Companies,](https://reader038.fdocuments.us/reader038/viewer/2022102707/56649e185503460f94b04b94/html5/thumbnails/1.jpg)
Microbiology: A Systems Approach
Chapter 11Physical and
Chemical Control of Microbes
PowerPoint to accompany
Cowan/Talaro
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
![Page 2: Microbiology: A Systems Approach Chapter 11 Physical and Chemical Control of Microbes PowerPoint to accompany Cowan/Talaro Copyright The McGraw-Hill Companies,](https://reader038.fdocuments.us/reader038/viewer/2022102707/56649e185503460f94b04b94/html5/thumbnails/2.jpg)
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Chapter 11
Topics- Controlling Microorganisms- Physical Control- Chemical control
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An overview of the microbial control methods.
Fig. 11.1 Microbial control methods
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Controlling Microorganisms
• Microbial agents• Sanitation• Effectiveness• Mode of action
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Microbial agents
• -static agents• -cital agents• Resistance• Terms• Effectiveness• Mode of action
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-static agents
• Temporarily preventing the growth of microbes– Bacteriostatic– Fungistatic
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-cital
• Killing or destroying a microorganism– Germicide – Bactericide
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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
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Comparing the resistance between endospores and vegetative cells to control agents.
Table 11.1 Relative resistance of bacterial endospors and vegetative cells
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Terms
• Sterilization• Disinfection• Antisepsis• Sanitation• Degermination
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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
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Disinfection
• Use of physical process or chemical agent (disinfectant) to destroy vegetative pathogens.
• Removes toxins• Not bacterial endospores
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Antisepsis
• Chemical agents (antiseptics) destroy or inhibit vegetative pathogens
• Skin and mucous membranes
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Sanitation
• Reducing the number of microorganisms
• Physical chemical agents
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Degermination
• Human skin - reducing the number of microorganisms
• Physical and chemical agents
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Effectiveness
• Number of microorganisms• Target population (bacteria, fungi,
spores, viruses)• Temperature and pH• Concentration of agent• Mode of action• Interfering agents (solvents,
debris, saliva, blood, feces)
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Factors that influence the effectiveness of antimicrobial agents.
Fig. 11.2 Factors that influence the rate at which microbesare killed by antimicrobial agents
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Mode of action
• Cell wall• Cell membrane• Nucleic acid synthesis• Protein synthesis• Protein function
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Cell wall
• Bacteria and fungi– Block synthesis– Degrade cellular components– Destroy or reduce stability
• Agent– Penicillin, detergents, alcohols
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Cell membrane
• All microbes and enveloped viruses– Bind and penetrate lipids – Lose selective permeability (leakage)
• Agent– Surfactants
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The effect of surfactants on the cell membrane.
Fig. 11.3 Mode of action of surfactants
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Nucleic acid synthesis
• Irreversible bind to DNA– Stop transcription and translation– mutations
• Agent– Chemical agent – formaldehyde– Physical agent – radiation
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Protein synthesis
• Binds to ribosomes– Stops translation– Prevents peptide bonds
• Agent– chloramphenicol
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Protein function
• Block protein active sites• Prevent binding to substrate• Denature protein• Agent
– Physical – Heat, pH change– Chemical – alcohols, acids, phenolics,
metallic ions
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The effects of heat, pH, and blocking agents on the function of proteins.
Fig. 11.4 Modes of action affecting protein function
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Physical Control
• Heat• Radiation• Filtration
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Heat
• Mode of action• Moist • Dry
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Mode of action
• Moist heat– Coagulation of proteins– Denaturation of proteins
• Dry heat– Dehydration– Denaturation– Oxidation (burning to ashes)
• Thermal death time
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Moist heat
• Steam and pressure• Tyndallization• Pasteurization• Boiling water
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Steam and pressure
• Pressure above normal atmospheric pressure will result in temperatures above 100˚C
• Effectively destroys spores• Sterilizes inanimate objects
(glassware)• Ex. Autoclave and home pressure
cooker
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A diagram of an autoclave.
Fig. 11.5 Steam sterilization with the autoclave
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Tyndallization
• Intermittent sterilization• Used for heat-sensitive media,
canned foods• Will not destroy spores• Ex. Exposure to free-flowing steam
for 30 to 60 minutes
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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
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Boiling water
• Decontaminates at 100 ˚C for 30 minutes
• Kills most non-spore forming pathogens
• Examples: home sanitizing and disinfecting, disinfecting unsafe water
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Dry heat
• Hot air• Incineration • Temperature and time of exposure
is greater than moist heat
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Hot air
• Hot air– Oven– Effective at 150˚C to 180˚C for 2-4
hrs– Effective for inanimate objects and
oils
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Incineration
• Destroys microbes to ashes or gas– Flame - 1870˚C– Furnace - 800˚C to 6500˚C
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An infrared incinerator uses flame to burn or oxidize materials into ashes.
Fig. 11.6 Dry heat incineration
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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
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Radiation
• Types of radiation • Modes of action• Applications
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Types of radiation
• Ionizing– Gamma rays (High energy)– X-rays (Intermediate energy)– Cathode rays (least energy)
• Nonionizing– Ultraviolet
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Mode of actions
• Ionizing radiation ejects orbital electrons from an atom– High energy
• Penetrates liquids and solids effectively
• Nonionizing radiation raises atoms to a higher energy state– Low energy
• Less penetration capability• Pyrimidine dimers
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The effects of ionizing and nonionizing radiation on DNA.
Fig. 11.7 Cellular effects of irradiation
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Ultraviolet (UV) radiation can cause the formation of pyrimidine dimers on DNA.
Fig. 11.9 Formation of pyrimidine dimers by the actionof UV radiation.
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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)
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A gramma radiation machine (ionizing radiation) used to sterilize fruits, vegetables, meats, fish, and spices.
Fig. 11.8 Sterilization with Ionizing Radiation
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A UV treatment system can be used to disinfect water.
Fig. 11.10 A UV treatment system for disinfection of water
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Filtration
• Removes microbes and spores from liquids and air
• Perforated membrane– Pore sizes vary
• Applications– Liquids that are sensitive to heat
• Serum, vaccines, media
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An example of a filtration system.
Fig. 11.11 Membrane filtration
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Chemical control
• Widely used agents• Applications
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Example of chemical agents, their target microbe, level of activity, and toxicity.
Table 11.5 Qualities of chemical agents used in health care
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Applications
• Halogens• Phenolics• Surfactants• Hydrogen peroxide• Detergents and soaps• Heavy metals• Aldehydes• Gases• Dyes, acids, and alkalis
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Halogens
• Chlorine– Disinfectant and antiseptic
• Disrupt sulfhydryl groups in amino acids
• Iodine– Topical antiseptic
• Disruption is similar to chlorines
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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,
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Phenolics contain a basic phenolic aromatic ring with different functional groups.
Fig. 11.12 Some phenolics
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Alcohols
• Ethyl alcohol, isopropyl (rubber alcohol)– 70% concentration dissolve
membrane lipids, disrupt cell surface tension, denatures proteins
• Germicidal and skin degerming
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Hydrogen peroxide
• Colorless and caustic liquid• Form hydroxyl free radicals
– Effective against anaerobes
• Skin and wound cleaner• Quick method for sterilizing
medical equipment
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Examples of different devices used to sterilize medical equipment.
Fig. 11.13 Sterile processing of invasive equipment protects patients.
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Detergents and soaps
• Quaternary ammonium (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
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For detergents, the positive charge region binds bacteria and the uncharged region integrates into the cell membrane.
Fig. 11.14 The structure of detergents
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Comparison between nongermicidal and germicidal soaps.
Fig. 11.15 Graph showing effects of handscrubbing
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Heavy metals
• Mercury, silver, – Inactivate proteins– Preservatives in cosmetics and
ophthalmic solutions
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Demonstration of the effects silver and gold have on microbial growth.
Fig. 11.16 demonstration of the oligodynamic actionof heavy metals.
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Aldehydes
• Glutaraldehyde– Crosslink with proteins on the cell
surface– Disinfectant for surgical instruments
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Representation of the action of glutaraldehyde.
Fig. 11.17 Actions of glutaraldehyde
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Gases
• Ethylene oxide– Reacts with functional groups of DNA
and proteins– Sterilizes and disinfects plastic
materials
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Examples of different devices that use gas to sterilize equipment.
Fig. 11.18 Sterilization using gas
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Dyes
• Crystal violet• Effective against Gram positive
bacteria• Ointments
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Acids and alkalis
• Acetic acid • Ammonium hydroxide• Prevents spore germination and
vegetative growth• Food preservative