Micro - Ch. 9

Define sterilization

• Process that destroys or removes all viable microorganisms (including viruses and endospores)

• Used for inanimate objects:

  • Surgical instruments, syringes, and commercially packaged food

• Ex:

  • Heat (autoclave)

  • Sterilants (chemical agents capable of destroying endospores)

Define disinfection

• Physical process or a chemical agent to destroy vegetative pathogens but not bacterial endospores

• Removes harmful products of microorganisms (toxins) from material

• Used on inanimate objects:

  • Boiling food utensils, 5% bleach solution on examining table, immersing thermometers in an iodine solution between uses

• Ex:

  • Bleach

  • Iodine

  • Heat (boiling)

Define decontamination (sanitization)

• Cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels

• Primarily used in food places such as restaurants that handle soiled utensils/containers:

  • Cooking utensils, dishes, bottles, cans

• Ex:

  • Soaps

  • Detergents

  • Commercial dishwashers

Define antisepsis (degermation)

• Reduces the number of microbes on the human skin

• A form of decontamination but on living tissues

• Involves scrubbing the skin (mechanical friction) or immersing it in chemicals (or both)

• Ex:

  • Alcohol

  • Surgical hand scrubs

What are considered the most resistant microbial structures?

• Endospores

• The goal of sterilization is the destruction of bacterial endospores

  • If it kills endospores, it will kill all less resistant microbial forms

Rank the relative resistance of microbial forms from more resistant to less resistant

1. Prions

2. Bacterial endospores

3. Mycobacterium

4. Staphylococcus and Pseudomonas

5. Protozoan cysts

6. Protozoan trophozoites

7. Most gram-negative bacteria

8. Nonenveloped viruses

9. Most gram-positive bacteria

10. Enveloped viruses

Explain endospores

• Function: resist heat, drying, freezing, radiation, and chemicals. Only formed under extremely stressful conditions in the cell

• Vegetative cell: metabolically active cells

• Endospores = metabolically inactive cell

What are critical medical devices?

• Expected to come into contact with sterile tissues

• Must be sterilized before use

What are semicritical devices?

• Come into contact with mucosal membranes

• Must receive high-level disinfection, preferably sterilized

What are noncritical devices?

• Do not touch the patient or only touch intact skin

• Require only low-level disinfection unless they become contaminated with blood or body fluids

What is the difference between microbicidal agents and microbistatic agents?

• Microbicidal: Agents that kill the microbe

• Microbistatic: Agents that only inhibit growth (removal = growth again)

Explain agents vs. processes

• Sterilization and disinfection are processes

• Agents used in the processes:

  • Bactericide

  • Fungicide

  • Virucide

  • Sporicide

  • Germicide/microbicide

Define bactericide

• Chemical that destroys bacteria except for those in the endospore stage. Irreversible

• Ex:

  • Alcohols

  • Phenolics

  • Quaternary Ammonium Compounds (Quats)

Define fungicide

• Chemical that can kill fungal spores, hyphae, yeasts

• Ex:

  • Chlorine compounds

  • Copper compounds

  • Hydrogen peroxide

Define virucide

• Chemical known to inactivate viruses, especially on living tissue

• Ex:

  • Halogens

  • Aldehydes

  • Sodium Hypochlorite

Define sporicide

• An agent capable of destroying bacterial endospores

• Ex:

  • Ethylene Oxide (EtO)

  • Peracetic Acid

  • Glutaraldehyde

Define germicide/microbicide

• Chemical agents that kill microorganisms

• Ex:

  • Formaldehyde

  • Chlorine dioxide

Define bacteristatic

Chemical agents that prevent the growth of bacteria on tissues or on objects in the environment. Reversible

What are the dry heat methods?

• Incineration - sterilization

• Dry oven - sterilization

Describe the incineration/dry oven method

• A flame is the most rigorous of all heat treatments

• The flame of a Bunsen burner reaches 1,870°C at its hottest point

• Reduces microbes and other substances to ashes and gas

• Sterilization

What is dry heat?

• Dehydrates the cell

• Denatures proteins (dry and moist heat)

• At very high temperatures, oxidizes cells, burning them to ashes

What are moist heat methods?

• Steam under pressure/autoclaving - sterilization

• Boiling water, hot water, pasteurization - disinfection

Describe the autoclave method

• Can be used for:

  • Glassware

  • Cloth (surgical dressings)

  • Metallic instruments

  • Liquids

  • Some media

• Cannot be used for:

  • Substances that repel moisture (oils, waxes)

  • Substances that are harmed by it (powders)

  • Heat-sensitive items (plastic Petri dishes)

• Sterilization

Describe the boiling water: disinfection method

• Boiling water bath can decontaminate items in the clinic and home

• 100°C will not kill all resistant cells - good for disinfection and not for sterilization

• Boiling water for 30 minutes will kill most non-endospore-forming pathogens

• Disadvantage: items can be easily recontaminated when removed from the water

• Disinfection

Describe the pasteurization: disinfection of beverage method

• Fresh beverages such as milk, fruit juices, beer, and wine are easily contaminated during collection and processing

• Because microbes have the potential for spoiling these foods or causing illness, heat is frequently used to reduce the microbial load

• Pasteurization is a technique in which heat is applied to liquids to kill potential agents of infection and spoilage, while at the same time retaining the liquid’s flavor and nutritional value

• Disinfection

Describe the effects of cold

• Principal benefit of cold treatment is to slow growth of cultures and microbes in food during processing and storage:

  • Cold merely retards the activities of most microbes

• Most microbes are not adversely affected by gradual cooling, long-term refrigeration, or deep-freezing

• Temperatures from -70°C to -135°C can preserve cultures of bacteria, viruses, and fungi for long periods

Describe the radiation method

• Radiation emitted from atomic activities and dispersed at high velocity through matter or space:

  • Gamma rays

  • X rays

  • Ultraviolet radiation

What are radiation methods?

• Ionizing: X ray, cathode, gamma - sterilization

• Nonionizing: UV - disinfection

Describe the filtration method

• Effective method to remove microbes from air and liquids

• Fluid is strained through a filter with openings large enough for the fluid to pass, but too small for microbes

• Used to prepare liquids that cannot withstand heat such as serum, vaccines, drugs, IV fluids, enzymes, and media

• Alternative method for decontaminating water, milk, and beer without altering their flavor

• High-efficiency particulate air (HEPA) filters are used in hospital rooms and sterile rooms