Control of Microbial Growth (Sterilization and Disinfection)
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Control of Microbial GrowthControl of Microbial Growth(Sterilization and Disinfection)(Sterilization and Disinfection)
Control of Microbial GrowthControl of Microbial Growth
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Microbial Control Microbial Control
Can inhibit growth of many microorganisms by washing and scrubbing with soaps and detergents.
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SterilizationSterilizationProcess of removing
or killing all microorganisms and viruses on or in a product.
– Ensures complete destruction of all microorganisms, including cells, spores, and viruses.
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Examples of SterilizationExamples of Sterilization
Dry heatAutoclavingGasVarious chemicalsCertain types of
radiation
Autoclave. www.lifelinemedical.net
Dry Heat Sterilization. www.kabdental.com
DisinfectionDisinfection Process that reduces # of
potential disease-causing bacteria and viruses on a material until they no longer present a hazard.
Terms decontamination and sanitation mean the same thing generally.
Disinfectant– A chemical used to disinfect
inanimate objects.
Example of Disinfection - Example of Disinfection - PasteurizationPasteurization
Method of disinfecting liquids.
Heat liquids to a certain temperature.
Does not totally destroy pathogens. Pasteurization Equipment.
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DecontaminationDecontamination
Inactivation or removal of both microbial toxins and the living microbial pathogens.
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AntisepticAntiseptic
Solutions used to disinfect skin and other living tissues.
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SanitationSanitation
Reduction of microbial populations to levels considered safe by public health standards. www.zerrenterprises.com
Microbicidal AgentsMicrobicidal Agents
The suffix –cide or –cidal refers to “killing.”
– Ex. Microbicidal agents (microbicides)
– Ex. Bactericidal agents
– Ex. Sporicidal agents
– Ex. Viricidal agents
Microbistatic AgentsMicrobistatic Agents
Microbistatic Agent Drug or chemical that inhibits the growth and reproduction
of microorganisms.
Bacteriostatic Agent One that specifically inhibits the metabolism and
reproduction of bacteria.
Microbistatic technique examples Ex. Lyophilization (freeze-drying) Ex. Rapid freezing (using liquid nitrogen)
Some Useful TermsSome Useful Terms Sepsis
Presence of pathogens in blood or tissues.
Asepsis Absence of pathogens. Ex. Hand washing; use of sterile gloves,
masks, gowns; sterilization of surgical equipment; use of disinfectants.
Antisepsis Prevention of infection.
Antiseptic technique Developed by Joseph Lister (1867). Use of antiseptics.
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Sterile TechniqueSterile Technique
Practice of excluding all microorganisms from a particular area, so that the area will be sterile.
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Controlling Microbial Growth Controlling Microbial Growth Using Physical MethodsUsing Physical Methods
Methods used to destroy or inhibit microbial growth may be physical or chemical.
Examples:HeatCombination of heat and pressureDesiccationRadiationSonic disruptionFiltration
HeatHeatPractical, efficient, and inexpensive method of
sterilization.
2 factors that influence effectiveness of heat for sterilization: temperature and time
– Thermal Death Point (TDP) Lowest temperature that will kill all organisms in a
standardized pure culture within a specified period.– Thermal Death Time (TDT)
Length of time necessary to sterilize a pure culture at a specified temperature.
Dry HeatDry Heat Heating materials in absence
of moisture.
Must be baked at 160º to 165ºC for 2 hours or at 170º to 180ºC for 1 hour.
Other methods include incineration and flaming surface of metal materials like forceps and loops.
biology.clc.uc.edu
Moist HeatMoist Heat Boiling or steaming.
Most pathogens destroyed after 30 minutes of boiling.
Boiling not always effective against some endospores and viruses.
Boiling not an option for thermophiles.
Boiling. ttt.astro.su.se
Steamer. www.appliancist.com
Autoclaving Autoclaving Large metal pressure
cooker that uses steam under pressure to completely destroy all microorganisms.
Increased pressure raises the temperature of boiling water (i.e. above 100ºC) producing steam.
www.uwm.edu
Home CanningHome Canning Use of a pressure
cooker.
If foods canned without pressure some bacterial endospores may survive.
i.e. Clostridium botulinum
www.thecookwarebarn.com
Bulging lid – botulism. calorielab.com
Disinfecting TechniquesDisinfecting Techniques
For clothing, bedding, and dishes
Use hot water with soap or detergent
Agitate solution around items
Combination of heat, mechanical action, and chemical inhibition kills most microbes. Washing Machine.
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Cold Cold Metabolic activities slowed.
Most microbes not killed, but growth inhibited.
Slow freezing not a good way to preserve bacteriological or biologic specimen.
Rapid freezing (liquid nitrogen) good for this.
Why should you not refreeze foods?
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Slow Freezing.
Rapid Freezing – liquid nitrogen. encarta.msn.com
DesiccationDesiccation
Process of drying materials.
Many microbes can remain viable despite absence of nutrients and moisture.
Ex. Lyophilization (freeze-drying)
Dried blood, fecal material, and dust may still contain viable microbes.
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Radiation Radiation Ultraviolet (UV) light sometimes used to
prevent or decrease microbial growth.X-rays and gamma and beta rays may be
used to destroy or prevent microbial growth.
www.fda.gov www.moondragon.org
Ultrasonic WavesUltrasonic Waves Often used to sterilize and clean delicate equipment.
Consists of tanks filled with liquid solvent (usually water).
Short sound waves are passed through liquid.
Sound waves dislodge organic debris.
Materials must then be washed and sterilized by another method.
Filtration Filtration Filters of various pore sizes are
used to filter or separate larger cells, larger viruses, bacteria, and other microbes from gases or liquids in which they are suspended.
Paper masks used to prevent the outward and inward movement of microbes.
wps.prenhall.com
health.howstuffworks.com
Gaseous AtmosphereGaseous Atmosphere
Altering atmosphere of microbes to inhibit growth.
Hyperbaric Chamber. www.perlhealth.com
Gas gangrene – caused by Clostridium spp. www.humanillnesses.com
Chemical Agents Used to Inhibit Chemical Agents Used to Inhibit Microbial GrowthMicrobial Growth
Temporarily or permanently.
Different disinfectants have different properties.
Disinfectants should be chosen based on their efficiency and effectiveness for a particular situation.
What Are Some Things to What Are Some Things to Consider When Choosing a Consider When Choosing a
Chemical Disinfectant?Chemical Disinfectant?
What makes an Ideal Chemical What makes an Ideal Chemical Antimicrobial Agent?Antimicrobial Agent?
How Do Disinfectants Kill How Do Disinfectants Kill Microorganisms?Microorganisms?
Some target and destroy cell membranes. Ex. Surface-active soaps and detergents; alcohols
Some destroy enzymes and structural proteins. Ex. Formaldehyde and ethylene oxide
Some attack cell walls or nucleic acids.
AntisepticsAntiseptics
Can be used safely on human skin.
Reduces # of organisms on the surface.
Does not penetrate pores or hair follicles.
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Preventing Growth of Pathogens Preventing Growth of Pathogens in Our Kitchensin Our Kitchens
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The Antibiotic Controversy The Antibiotic Controversy
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The EndThe End