Sterilization/Disinfection

What are the two types of Sterilization/Disinfection

Two types

• Physical

  • heat, irradiation, filtration, mechanical removal (washing)

• Chemical

  • Use of any one of a variety of antimicrobial chemicals

Define:

• Sterilization

• Disinfection

• Sanitized

• Preservation

Definitions:

• Sterilization: process of removing (destroying) all microorganisms

• Disinfection: process which eliminates most (or all) disease-causing microorganisms and viruses on a surface

  • Biocides or (germicides)

  • Antiseptics: Disinfectants used on body surfaces (skin)

• Sanitized: substantially-reduced numbers of microbes

  • Items are “clean” in appearance

• Preservation: Delay spoilage of foods

What is Selection of an antimicrobial procedure is based on:

1. Type of microorganism

2. Number of microorganisms

3. Environmental conditions

4. Potential risks of infection

1. Describe the type of microorganisms and how they’re hard to disinfect

   • Bacterial endospores

   • Waxy Cell wall

   • Pseudomonas sp.

   • Naked Viruses

2. Describe how the environmental conditions can affect sterilization

3. Describe the different categories of potential risk of infection

Types:

• Bacterial endospores

  • Highly resistant to standard sterilization treatments

  • Req. extreme heat + chemical treatments

• Waxy cell wall (Mycobacterium)

  • Resistant to many chemical treatments

  • Require toxic forms of disinfectants

• Pseudomonas sp.

  • can grow in presence of disinfectants

  • Common cause for hospital-acquired (nosocomial) infections

• Naked viruses (lack a lipid envelope)

  • More resistant to disinfectants (polioviruses)

    • Enveloped viruses (HIV) is less resistant

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Env. conditions:

• Presence of dirt, grease, and body fluids can interfere

• Therefore must clean items before sterilizing

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Categories of Potential Risk of Infection

• Critical

  • direct contact, penetration of body tissues

    • Needles, scalpels

• Semi-critical

  • contact w/ mucus membranes but does not penetrate

    • Endoscopes, endotracheal tubes

• Non-critical

  • contact with unbroken skin

    • Countertops, stethoscopes

Describe the different methods of Sterilization

• Boiling Water

• Pasteurization

• Ultra-high-temperature method

• Autoclave

• Flash Autoclave

• Dry heat

How do you know sterilization is complete?

Sterilization Techniques:

• Boiling water

  • 100 degC, 10 min

• Pasteurization

  • Function:

    • Reduction of microorganisms which cause spoilage

      • Tuberculosis, salmonellosis, typhoid fever

    • NOTE: HISTORY: originally used to moderately heat wine to reduce the number of microorganisms present in wine

  • Method:

    • 62 degC, 30 minutes

    • 72 degC, 15 seconds

• Ultra-high-temperature method

  • Function:

    • for Products such as single-serving cream containers

      • Lunch-size milk and boxed juices

  • Method:

    • 140-150 degC for a few seconds, then cooled → aseptically packaged

• Pressurized steam (autoclave)

  • Mech:

    • Heated water forms steam → pressure → increased temperature

      • can kill endospores

  • Method:

    • 15 psi, 121 degC for 15 minutes

• Flash Autoclaving (rapid sterilizing)

  • Method

    • 135 degC, for 3 minutes

      • 132 degC under pressure for approximately 4.5 hrs is believed to destroy prions

• Dry Heat:

  • Flame-sterilizing an inoculating loop

  • Glass Petri dishes + pipettes are sterilized in ovens at temperatures in the range of 160 degC to 170 degC

    • can damage + deform

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Sterilization indicators:

• test using Bacillus stearothermophilus (optimal growth @ 55 degC)

Describe the different Germicidal Chemicals

• Alcohols

  • Not effective against

  • Mech:

• Aldehydes

  • Mech:

  • Uses:

  • Drawback:

• Ethylene oxide (gas)

  • Mech:

  • Uses:

  • Drawback:

• Halogens

  • Chlorine

    • Ex:

    • Uses:

    • Drawback:

  • Iodine

    • Mech:

• Hydrogen peroxide

  • Uses:

  • Drawback:

• Phenol compounds

  • Mech:

  • Drawback:

• Quaternary ammonium compounds (Quats)

  • Mech:

Germicidal Chemicals

• Alcohols

  • Not effective against

    • bacterial endospores,

    • naked viruses

  • Mech:

    • coagulating enzymes + essential proteins → damages lipid membranes

• Aldehydes

  • Mech:

    • Inactivates proteins and nucleic acids

  • Uses:

    • 2% alkaline glutaraldehyde: treat heat-sensitive medical items

      • 10-12 hrs immersion kills all microbial life, endospores, and viruses

  • Drawback: Toxic

• Ethylene oxide (gas)

  • Mech:

    • Reacts with proteins

  • Uses:

    • Kills microbes, endospores, viruses

    • Penetrates well into a variety of materials

      • implants, pacemakers, electrical equipment, disposables

  • Drawback: Mutagenic

• Halogens

  • Chlorine

    • Ex:

      • 10% bleach – cheap, effective for disinfecting surfaces

    • Uses:

      • Destroys all types of microorganisms, viruses

    • Drawback:

      • Irritating to skin and mucus membranes

  • Iodine

    • Mech:

      • Linked to carrier molecules (iodophores)

        • In this way, not as irritating to skin

• Hydrogen peroxide

  • Uses:

    • good disinfectant

  • Drawback:

    • Cells that uses aerobic metabolism → inactivate hydrogen peroxide via catalse

      • however, enzyme activity is low in microorganisms

• Phenol compounds

  • Mech:

    • Destroy cytoplasmic membranes of microorganisms

    • Denatures proteins

    • Wide range of activity, including Mycobacterium

  • Drawback: Irritating to skin, unpleasant odor

• Quaternary ammonium compounds (Quats)

  • Mech:

    • Cationic detergents

      • Attracted to (-) charged cell surfaces of many microorganisms → rxt w/ cell membranes

        • Reduces Liquid surface tension → efficient in washing away organic material

Describe how filtration can be used to sterilize microorganisms

• Filters

  • Composed of

  • Mech

  • USes

• List the uses of HEPA

filters:

• Composed of:

  • inert materials such as cellulose acetate, cellulose nitrate, polycarbonate

• Mech:

  • Contain pores of varying sizes → microbes of certain sizes (0.2 – 0.45 microns) gets stuck

• Uses:

  • sterilize liquids which are heat-sensitive

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HEPA (High-efficiency particulate air filters)

• Uses:

  • Removes microorganisms greater than 0.3 microns in size

  • specialized hospital rooms

  • Biological safety cabinets

  • Laminar flow hoods

  • handling infectious microorganisms

Describe how radiation can control microbial growth

• X rays

• Gamma Rays

• UV

• X-rays

  • Short wavelengths, high energy

• Gamma rays

  • Produces reactive molecules

    • superoxide, hydroxyl free radicals

• Ultraviolet

  • Damages DNA by creating thymine dimers

    • difficult for DNA replication

How does one make a non-perishable

1. Chemical

   • Benzoic, sorbic, propionic acids

   • Nitrates, nitrites

     • Hazrdous b/c conversion to nitrosamines (carcinogenic) via heat

2. Low-temperature

   • Growth = temperature-dependent

   • Enzyme Inhibition

   • ice damages microbial cells

3. Reducing water availability

   • Adding salt or sugar

   • Drying, lyophilization (freeze-drying)