Biomedical Sciences: Chemical Control of Microbes (Lecture 3; Exam 1)

Sterilization

A process that destroys or removes ALL viable microorganisms.

Types of Sterilization

• Physical: Heat, ionizing radiation, filtration

• Chemicals: Ethylene oxide (gas), aldehydes (glutaraldehyde), peroxygen compounds.

  • Must rinse off glutaraldehyde or peroxides from instruments prior to using on a patient.

  • Requires prolonged time.

Disinfection

Elimination of most microorganisms that can cause disease.

Defined as the destruction of pathogenic microorganisms on INANIMATE surfaces.

• Does NOT eliminate all microorganisms.

• Usually uses chemical disinfectants (germicides).

Antiseptics

For use on living tissues.

Sanitization

*Low level disinfection

The use of chemicals to reduce the numbers of bacteria on inanimate surfaces to levels considered safe for public health.

Surface Barriers

Material that prevents the penetration of microorganisms, particulates and fluids.

Examples of surface barriers:

• Plastic food wraps

• Custom-made covers

• Sealable “zip-lock” bags

• Avoids contamination of surfaces

Difficulty of Decontamination

• Prions

• Bacterial spores

• Non-enveloped viruses

• Vegetative bacterial cells, enveloped viruses, yeasts and fungi

What is the most resistant to decontamination?

Prions - Responsible for mad cow disease

What is the least resistant to decontamination?

Vegetative (growing) bacterial cells, enveloped viruses, yeasts and fungi.

Examples of Evneloped Viruses

Lipophilic

• HIV

• Herpesviruses (HSV)

• Hep B virus (HBV)

• Hep C virus

• Influenza viruses

Examples of Non-enveloped Viruses

Hydrophilic

• Rhinoviruses

  • common cold

• GI Viruses

  • rotavirus

  • norovirus

• HPV - wart viruses (like HPV)

• Hep A virus (HAV)

• Enteroviruses (like hand-foot-and-mouth disease)

• Adenoviruses

Clinical Contact Surface

A surface contaminated from patient materials or contact by healthcare personnel’s gloved hands.

Ideal Disinfectant Traits

***No single disinfectant can meet all needs***

• Broad spectrum

• Fast-acting

• Not affected by physical factors

• Nontoxic

• Hypoallergenic

• Surface compatibility

• Residual effect on treated surfaces

• Ready to use

• Odorless

• Economical

Bioburden

• Organic material present in body fluids, esp. saliva and blood.

• Forms protective covering on microorganisms and allows them to survive in the environment longer.

Levels of Disinfectants

• Hospital disinfectant

• Low-level disinfectant

• Intermediate-level disinfectant

• High-level disinfectant

Hospital Disinfectant

For use on inanimate objects in hospitals.

• Efficacy demonstrated against Salmonella enterica, Staphylococcus aureus, and Pseudomonas aeruginosa.

Low-level Disinfectant

Registered as a hospital disinfectant.

• + potency against HIV and HBV (both enveloped viruses)

  • HBV (hep b virus)

Intermediate-level Disinfectant

Registered as a hospital disinfectant but is NOT effective against bacterial spores.

• + potency against HIV, HBV

• + potency against Mycobacterium tuberculosis ***

  • -tuberculocidal

• Can be expected to inactivate vegetative bacteria, most fungi, and enveloped viruses. (typically NOT effective against non-enveloped viruses)

High-level Disinfectant

Registered for use on critical and semi-critical patient care devices.

• Inactivates vegetative bacteria, mycobacteria, fungi, all viruses, and spores BUT not necessarily large numbers of bacterial spores.

• Some can be sterilants when used for a longer contact time.

• NOT recommended for disinfection of clinical contact surfaces.

Disinfection: 2-Step Process

• Must clean before disinfecting

• Spray-wipe-spray

***Allow to set for the recommended disinfection time.

Chemical Disinfectant Types

• Chlorine compounds

• Iodine and iodophors

• Phenol and phenolics

• Bisguanides

• Alcohols

• Quaternary ammonium compounds (QUATS)

• Aldehydes

  • Glutaraldehyde

• Hydrogen Peroxide

• Peracetic acid

• Ethylene oxide

Chlorine Compounds

Oxidize and denature enzymes/proteins.

• Kills bacteria, bacterial spores, fungi and viruses.

• Unstable when exposed to light, alkaline pH, organic matter.

Halogen antimicrobials:

• Fluorine

• Chlorine

• Bromine

• Iodine

Advantages of Hypochlorite

(OCl-; present in diluted bleach)

• Rapid antimicrobial action

• Broad spectrum

• Effective in dilute solution

  • 1:10 - 1:100 dilution of bleach (6.25%)

• Can often kill spores

• Economical

Disadvantages

• Must prepare fresh dilutions daily!!

• Chemically unstable

• Irritating to skin and eyes

• Corrosive to metals

• Damages clothing, plastics, rubber

• Unpleasant, persistent odor

• Activity diminished by organic matter

Iodine and Iodophors

• Halogen antimicrobials

• Oxidize and denature proteins

• 2 preparations: Iodine solution and iodophors

• Aqueous iodine and iodine tincture used as a topical antiseptic.

  • Can be extremely irritating to the skin; no longer recommended for routine antiseptic.

Advantages of Iodophors

• Broad spectrum

• Residual biocidal action

• Biocidal within 5-10mins

• Effective in dilute solutions

• Few reactions

• Maintains surface moistness

Disadvantages of Iodophors

• Daily preparation necessary

• Discoloration of some surfaces

• Inactivated by hard water

• NOT a sterilant

• Unstable at high temps

• Dilution & contact time critical

• Rust inhibitor necessary

Phenol and Phenolics

Phenol or carbolic acid first used by Joseph Lister as a surgical germicide. Highly toxic!!

• Strongly microbicidal - disrupts cell walls, membranes, precipitate proteins.

• Broad antimicrobial spectrum (not sporicidal)

  • May be low to intermediate level of disinfectant depending on preparation

• Phenolics have added groups (makes them loss toxic than original phenol; such as Cl-)

Advantages of Synthetic Phenolics

• Broad spectrum

• Tuberculocidal

• Useful on metal, glass, rubber, plastic

• Residual biocidal activity

Disadvantages of Synthetic Phenolics

• Not sporicidal

• Diluted ones may need to be prepared fresh daily. Some have longer use life.

• Able to degrade certain plastics, etch glass with prolonged exposure.

• Difficult to rinse off certain materials.

• Film accumulation

• Skin and eye irritation

Bisguanides

Disrupt membranes but are NOT phenolics.

• Common compound is Chlorohexidine.

  • Used as skin antiseptic or mouth rinse

  • Periogard, Hibiclens, Hibitane

Alcohols

Only ethyl and isopropyl alcohol suitable for microbial control.

• Concentrations of 50% or higher dissolve membrane lipids, disrupt surface tension, compromise membrane integrity. Once in cytoplasm, denatures proteins —> leads to coagulation.

What type of alcohol is NOT effective against non-enveloped viruses?

Isopropyl alcohol

What type of viruses is ethyl alcohol active against?

BOTH non-enveloped viruses and enveloped viruses.

What is the best microbicidal concentration for alcohols?

70% alcohol (30% water)

100% ALCOHOL IS NOT A PROTEIN COAGULANT.

Advantages of Alcohols

• Rapidly bactericidal

• Tuberculocidal and virucidal; (virucidal activity depends on alcohol used)

• Only slightly irritating

• Benefits from positive historic perception

• Economical

Disadvantages of Alcohols

• Not sporicidal

• Diminished activity with bioburden

• Damaging to certain materials, including rubber and plastics

• Rapid evaporation rate

• Isopropanol only kills enveloped viruses

Quaternary Ammonium Compounds (Quats)

Surface active detergents - alter membrane permeability. (Low level disinfectants)

• Effect enzymes and cell permeability

• Bactericidal against gram-POSITIVE bacteria but NOT all gram-negative bacteria.

  • Does NOT kill pseudomonas.

• Higher concentrations are toxic for humans.

• Good cleaning agents

• Accepted when combined with alcohol as tuberculocidal (Quat alcohol)

Advantages of Quats

• Bactericidal (kills bacteria) against gram-positive bacteria

• Active against enveloped viruses

• Pleasant odor

• Low tissue toxicity

Disadvantages of Quats

• Not tuberculocidal, sporicidal, or virucidal against non-enveloped viruses.

• Inactivated by anionic detergents (soaps, hard water)

• Inactivated by organic matter

• Variable activity against gram-negative bacteria.

• Damaging to plastics, upholstery

• Expensive if wipes used for disinfection of large areas

Cavicide: Biocidal Effectiveness

***3 minutes for bacteria, 2 minutes for viruses***

Aldehydes

Organic substances with a -CHO functional group.

• Glutaraldehyde and formaldehyde

• Cross-link protein molecules and disrupt enzymes

  • Kill by alkylating protein and DNA (add CH3,-CH2-CH3, etc.)

• Glutaraldehyde

• Tissue fixatives; Extremely irritating to skin

Glutaraldehyde

Is a sterilant with long term exposure or a high-level disinfectant with a shorter exposure.

Advantages of Glutaraldehyde

• Registered as a chemical sterilant

• Capable of killing spores at room temp after 10hrs

• Active in presence of organic matter

• Prolonged activated life (use life)

• Useful for sterilization of heat-liable items

• Useful for high-level disinfection of certain heat-sensitive items

Disadvantages of Glutaraldehyde

• Prolonged interval required for sterilization

• Items must be rinsed with sterile water

• Not an environmental surface disinfectant

• Severe tissue irritation and toxicity from fumes

• Allergenic

• Discolors some metals

• Reuse life varies with bioburden

• Cannot package items

• Can be corrosive

Hydrogen Peroxide/ Peracetic Acid

Produces highly reactive hydroxyl free-radicals that damage proteins.

• 7.5% hydrogen peroxide is approved as a high-level disinfectant/sterilant.

  • Antiseptic at low concentrations.

• Both are active against a wide range of organisms: bacteria, yeasts, fungi, viruses, bacterial spores

Hydrogen Peroxide (7.5%)

• High level disinfection in 30mins at 20C

• Sterilization (extensive spore killing) requires 6hours (CDC)

Peracetic Acid

• High level disinfection in 30mins at 20C

• Sterilization (extensive spore killing) in 30mins with 1% peracetic acid

Shelf Life

Time that a product may be stored (in its concentrated form) and retain its activity.

Use Life

Life expectancy of a solution once it has been activated (after diluting to working solution).

Reuse Life

Amount of time that a solution can be used and reused as it is challenged with instruments that or wet or coated with bioburden.

Sterilizing Gases

• Ethylene oxide, propylene oxide

• Strong alkylating agents

• High level disinfectant/sterilant

• Sterilize and disinfect plastics and prepackaged devices, foods

Advantages of Ethylene Oxide

• High capacity for penetration

• Does not damage heat-liable materials

• Evaporates without leaving a toxic residue

• Suitable for materials that cannot be exposed to moisture

Disadvantages of Ethylene Oxide

• Slow; requires long cycle time (10-16 hrs)

• Uses toxic/hazardous/explosive chemical

• Items must be cleaned and dried thoroughly before exposure

• Retained in liquids and rubber materials for prolonged intervals

• Causes tissue irritation if not well aerated

Disinfectant Levels of Chemical Agents

• Chlorine compounds -int to high

• Iodophors - int

• Phenolics - low to int

• Alcohols - int

• Quaternary ammonium compounds - low

• Quat-alcohols - int

• Glutaraldehyde -high

• Hydrogen peroxide - low tohigh

• Peracidic acid - high

• Ethylene oxide (a gas) - high

Critical patient-care Instruments

Penetrates soft-tissue, contacts bone, or enters otherwise sterile areas.

• Heat sterilize

Semi-Critical Patient care instruments

Touches mucous membranes - heat sterilize.

If heat sensitive, high-level disinfection or use disposable single-use sterile instrument.

Non-critical patient care instruments

Contact intact skin.

• If no blood, disinfect with hospital-level or low level disinfectant.

• If visibly contaminated, disinfect with intermediate-level disinfectant.

Antimicrobial Actions: Cytoplasmic Membrane

• Phenolics

• Quats

  • Bisguanides

  • Alcohols

Antimicrobial Actions: Proteins

• Alcohols

• Aldehydes

• Halogens

• Metals

• Ozone

• Peroxygens

• Phenolics

Antimicrobial Actions: DNA

• Ethylene oxide

• Aldehydes