Control of Microbial Growth (Sterilization and Disinfection)

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Control of Microbial Growth(Sterilization and
Disinfection)
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Control of Microbial Growth
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Microbial Control

• Can inhibit growth of many microorganisms by
  washing and scrubbing with soaps and detergents.

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Sterilization

• Process 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 Sterilization

• Dry heat
• Autoclaving
• Gas
• Various chemicals
• Certain types of radiation

Autoclave. www.lifelinemedical.net
Dry Heat Sterilization. www.kabdental.com
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Disinfection

• 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.

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Example of Disinfection - Pasteurization

• Method of disinfecting liquids.
• Heat liquids to a certain temperature.
• Does not totally destroy pathogens.

Pasteurization Equipment. www.foodprocessing-techn
ology.com
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Decontamination

• Inactivation or removal of both microbial toxins
  and the living microbial pathogens.

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Antiseptic

• Solutions used to disinfect skin and other living
  tissues.

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Sanitation

• Reduction of microbial populations to levels
  considered safe by public health standards.

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Microbicidal Agents

• The suffix cide or cidal refers to killing.
• Ex. Microbicidal agents (microbicides)
• Ex. Bactericidal agents
• Ex. Sporicidal agents
• Ex. Viricidal agents

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Microbistatic 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)

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Some 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 Technique

• Practice of excluding all microorganisms from a
  particular area, so that the area will be sterile.

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Controlling Microbial Growth Using Physical
Methods

• Methods used to destroy or inhibit microbial
  growth may be physical or chemical.
• Examples
• Heat
• Combination of heat and pressure
• Desiccation
• Radiation
• Sonic disruption
• Filtration

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Heat

• Practical, 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.

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Dry 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
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Moist 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
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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.

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Home Canning

• Use of a pressure cooker.
• If foods canned without pressure some bacterial
  endospores may survive.
• i.e. Clostridium botulinum

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Bulging lid botulism. calorielab.com
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Disinfecting 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. www.genexe.com
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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?

www.themodernapprentice.com
Slow Freezing.
Rapid Freezing liquid nitrogen. encarta.msn.com
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Desiccation

• 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

• 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.

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www.fda.gov
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Ultrasonic 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.

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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.

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Gaseous Atmosphere

• Altering atmosphere of microbes to inhibit
  growth.

Gas gangrene caused by Clostridium spp.
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Hyperbaric Chamber. www.perlhealth.com
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Chemical Agents Used to Inhibit Microbial Growth

• Temporarily or permanently.
• Different disinfectants have different
  properties.
• Disinfectants should be chosen based on their
  efficiency and effectiveness for a particular
  situation.

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What Are Some Things to Consider When Choosing a
Chemical Disinfectant?
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What makes an Ideal Chemical Antimicrobial Agent?
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How Do Disinfectants Kill 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.

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Antiseptics

• 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 in Our Kitchens
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The Antibiotic Controversy
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The End