Chemical Disinfection

衛生署 疾病管制局中區傳染病防治醫療網王任賢 指揮官

Chemicalsn Use depends on

spectrum of antimicrobial activity and compatibility with materials

n Also limited by dangers of chemicals themselves

n Examplesn Halogensn Alcoholsn Alkylating agentsn Ethylene oxiden Phenolicsn cetrimide (QAC)n chlorhexidine

(diguanide)

The Ideal Disinfectant

Ø Resistant to inactviationØ Broadly active (killing pathogens)Ø Not poisonous (or otherwise harmful)Ø Penetrating (to pathogens)Ø Not damaging to non-living materialsØ StableØ Easy to work withØ Otherwise not unpleasant

Disinfectant殺菌效果之決定因素Ø Disinfectant concentrationsØ Length (time) of administrationØ Temperature during administration (usual chemical reaction

2x increase in rate with each 10°C increase in temperature)Ø Microbe type (e.g., mycobacteria, spores, and certain viruses

can be very resistant to disinfection—in general vegetative cells in log phase are easiest to kill)

Ø Substrate effects (e.g., high organic content interferes with disinfection—stainless steel bench easier to disinfect than turd)

Ø It is easier (and faster) to kill fewer microbes than many microbes

Factors determining usefulness of chemical disinfection

n Spectrum of antimicrobial activityn is it the right agent for the job?

n Used at correct concentrationn concept of 'in use concentration’n diluted down from high concentrationn stored for <24 hoursn no topping up of old solutions

Factors determining usefulness of chemical disinfectionn Time of exposure

n You cannot disinfect an endoscope in 5 minutes glutaraldehyde!

n Correct pH?n Inactivating materials

n Pus, blood vomit, cork, soaps etcn Is disinfectant sterile?

n Many cases of Gram-negatives living in disinfectants!

n Microbiological “in-use” testing

Used for sterilizing medical suppliesDNA damageRadiation, X-rays

Line-drying laundryStrong vis. Light

Limited penetrationDNA damage (thymine dimers)Radiation, UV

Used in food preservation (less effective against fungi)

Plasmolysis of contaminantsOsmotic Pressure, Addition of salt or sugar

BacteriostaticDecreased chemical reaction rate

Cold, Refrigeration

Used for food & drug preservation; Does not necessarily kill so used for Long-term storage of bacterial cultures

Desiccation and low temperature

Cold, Lyophilization(also desiccation)

Used for heat sensitive liquidsSeparation of bacteria from liquid (HEPA: from air)

Filtration

170°C for 2 hours; Used for glassware & instrument sterilization

Oxidation & Denatures proteins

Dry Heat, Hot air oven

Used for inoculating loopIncineration of contaminantsDry Heat, Flaming

Kills pathogens in food productsDenatures proteinsMoist Heat, Pasteurization

121°C at 15 p.s.i. for 30 min kills everything

Denatures proteinsMoist Heat, Autoclaving

Kills vegetative bacterial cells and viruses Endospores survive

Denatures proteinsMoist Heat, boiling

CommentsMechanisms of ActionAgent

Mold and Fungi inhibitors; e.g., benzoate of soda

High/low pHOrganic acids and bases

Antiseptic - benzalconium chloride, Cepacol; Disinfectant

Denature proteins; Disrupts lipids

Quats (cationic detergent)

Disinfectant, Irritating odorDisrupts cell membranePhenolics

Antiseptic & Disinfectant; Silver NitrateDenature proteinHeavy MetalsAntiseptic - Iodine (Betadine) Disinfectant - Chlorine (Chlorox)

Oxidizing agent Disrupts cell membrane

Halogens

Antiseptic & Disinfectant Ethanol and isopropyl

Denatures proteins; Disrupts lipids

Alcohols

Gluteraldehyde - disinfectant (Cidex); Formaldehyde - disinfectant

Denature proteinsAldehydes

Used in a closed chamber to sterilizeDenaturing proteinsEthylene OxideHydrogen peroxide – antiseptic; Hydrogen peroxide – disinfectan; Benzoyl peroxide – antiseptic

Denature proteinsOxidizing agents

Soaps; detergentsMembrane Disruption; increased penetration

SurfactantsCommentsMechanisms of ActionAgent

Selection criteria (chemical antimicrobial agents)

n Antimicrobial efficacyn Corrosivityn Chemical hazardn Environmental concernsn Use solution pHn Stability

Biocidal spectrum

Corrosivity

Chemical hazard

Environmental concerns

Stability

Surfactants

Soap and Detergentsn Soaps are sodium or potassium salts of fatty

acids, a natural productn Detergents, instead, are artificial surfactantsn While soaps are always negatively charged,

some detergents are negatively charged while others are positively charged

n One example of a positively charged detergent are quaternary ammonium compounds (a.k.a., quats)

Chlorhexidine (a diguanide) n Used as general purpose

antiseptic for skin and mucous membranes in many formulations, e.g. Hibiscrub, Hibisol, Savlon

n Advantages: relatively non-toxic and good against S. aureus

n Disadvantages: can support growth of e.g. P. aeruginosa

Phenolics & QACsn Clear soluble phenolics (e.g. Hycolin) used

as disinfectant on soiled surfaces, relatively inactive against spores and viruses

n Hexachlorophane used as surgical scrubn Quaternary ammonium compounds, e.g.

cetrimide usually only used in combination with other agents; good detergent properties.

u Phenol (carbolic acid) was first used by Lister as a disinfectant.u Rarely used today because it is a skin irritant and has strong

odor.u Used in some throat sprays and lozenges (錠劑). u Acts as local anesthetic.

u Phenolics are chemical derivatives of phenolu Cresols: Derived from coal tar (Lysol).u Biphenols (pHisoHex): Effective against gram-positive

staphylococci and streptococci. Used in nurseries. Excessive use in infants may cause neurological damage.

u Destroy plasma membranes and denature proteins.u Advantages: Stable, persist for long times after applied,

and remain active in the presence of organic compounds.

Phenols and Phenolics

Phenol, Carbolic Acid, & Phenolicsn Phenol (carbolic acid) and derivativesn Affect plasma membrane, inactivates enzymes, and

denature proteinsn Stable, persistant, and especially effective when

dealing with disinfecting materials contaminated with organics…

n … but leave residual films, can irritate skin, don’t kill endospores, and are corrosive to rubber and plastics

n Some phenolics are mild enough for use as antiseptics while others are too harsh or otherwise dangerous to be employed on living tissue

n Hexachlorophene, Triclosan, Lysol, soap

Quaternary Ammonium Compounds (Quats)u Widely used surface active agents.u Cationic (positively charge) detergents.u Effective against gram positive bacteria, less effective

against gram-negative bacteria.u Also destroy fungi, amoebas, and enveloped viruses.u Zephiran, Cepacol, also found in our lab spray bottles.u Pseudomonas strains that are resistant and can grow

in presence of Quats are a big concern in hospitals.u Advantages: Strong antimicrobial action, colorless,

odorless, tasteless, stable, and nontoxic.u Diasadvantages: Form foam. Organic matter

interferes with effectiveness. Neutralized by soaps and anionic detergents.

Ø Quats are cationic detergents that act by disrupting lipid bilayers

Ø Quats are bactericidal, fungicidal, viricidal (enveloped), and amoebicidal

Ø Quats are most effective against Gram-positive bacteriaØ Quats do not kill endospores, Mycobacteria spp., nor

non-enveloped virusesØ Quats are rapidly inactivated by organics including

cotton and soapØ Zephiranà Benzalkonium chlorideØ CepacolàCetylpyridinium chloride

Quats

Halogensn Hypochlorites

(household bleach) & chlorine

n Advantagesn active against viruses,

spores, fungi

n Disadvantagesn inactivated by organic

matter, freshness & pH critical (go off if diluted), corrosive to metals

n Practical Usesn 0.1% hypochlorite used as

general disinfectantn Strong hypochlorite (0.25%)

used in lab & on woundsn Extra strong (1%) used on

HBV blood spillsn Chlorine used to treat

drinking water and control Legionella

Halogensn Two halogens are regularly employed as

antimicrobials: Iodine and Chloriden Iodine: commonly used as an antiseptic against all

microbes, fungi, and virusesn Iodine: It inhibits protein synthesis and oxidizes –SH

groups of amino acidsn Chlorine: Used as a disinfectant (10% bleach)n Chlorine: Hypochlorous acid (HOCl) is a product,

formed in water, that is the active form of the disinfectant

n Chlorine: Applied in treatment of drinking water, swimming pool, and sewage

Halogensn Iodophors & iodinen Advantages

n Some activity against viruses, spores, fungin Disadvantages

n inactivated by organic matter, can stain skin, irritant, expensive

n Practical Usesn Pre-op skin disinfectionn Povidone iodine used as surgical scrub, as

powder on ulcers

A. Iodine:u Tincture of iodine (alcohol solution) was one of first

antiseptics used.u Combines with amino acid tyrosine in proteins and

denatures proteins.u Stains skin and clothes, somewhat irritating.u Iodophors: Compounds with iodine that are slow

releasing, take several minutes to act. Used as skin antiseptic in surgery. Not effective against bacterial endospores.u Betadineu Isodine

Halogens Effective alone or in compounds

Halogens Effective alone or in compounds

B. Chlorine:u When mixed in water forms hypochlorous acid:

Cl2 + H2O ------> H+ + Cl- + HOClHypochlorous acid

u Used to disinfect drinking water, pools, and sewage.u Chlorine is easily inactivated by organic materials.u Sodium hypochlorite (NaOCl): Is active ingredient

of bleach.u Chloramines: Consist of chlorine and ammonia.

Less effective as germicides

Chlorinationn 1744 discovered in Swedenn 1810 identified as an elementn 1835 first used to control odorsn 1890’s started to be used as a disinfectantn 1896 earliest recorded use in experiments on water suppliesn 1897 used in England to sterilize water mains following typhoid

outbreakn 1902 first continuous use in water supplies in Belgiumn 1909 liquid chlorine (compressed gas) became commercially

availablen Subsequent rapid spread in use of chlorine throughout the worldn WWI: Chlorine gas used as chemical warfare ag

Chlorination and Typhoid fever

Chlorinationn Hypochlorite may either be added directly (i.e., in the form of

bleach) or created within water by bubbling chlorine gas throughthe water

n Chlorine gas - preferred for medium to large disinfection systems

n Sodium Hypochlorite (liquid) - typically used for small disinfection systems and large swimming pools

n Calcium Hypochlorite (powder, tablet) - typically used for private swimming pools

n For water purification, do not use scented bleachn Bromine sometimes used as a less-smelly alternativen Hypochlorite is less effective in the presence of significant

organic compounds

Chlorinationn “What is known as modern chemical warfare began during

World War I. The first chemical agent to be used was large amounts of chlorine gas, about one hundred sixty tons, which was released from 6,000 pressurized cylinders into the wind by the Germans against the Allies. The chlorine floated in a huge clouds toward the Allies until it reached the Allied lines causing men to die from the effects of the chlorine gas. Because of the large amounts of gas released the chlorine caused large amounts of yellowish fluid to form in the lungs of its victim, also causing eye, nose, and throat burning before causing death by choking.”

n http://www.geocities.com/CapeCanaveral/Lab/4239/chemweapons/history.html

Iodine

Iodophores

Alcoholsn Isopropanol & ethanoln Advantages

n kill vegetative bacteria on clean surfaces in 30 seconds

n Disadvantagesn inactive against spores, fungin Inflammablen Need to be at correct % with water (65-80%)

n Practical usesn Skin antisepsis before venepuncturen Hand rubsn Disinfection of e.g. trolley tops

Alcoholsu Kill bacteria, fungi, but not endospores or naked

viruses.u Act by denaturing proteins and disrupting cell

membranes.u Evaporate, leaving no residue.u Used to mechanically wipe microbes off skin before

injections or blood drawing.u Not good for open wounds, because cause proteins

to coagulate.u Ethanol: Drinking alcohol. Optimum concentration is 70%u Isopropanol: Rubbing alcohol. Better disinfectant than

ethanol. Also cheaper and less volatile.

Alcoholsn Aqueous ethanol (60-95%) and isopropanol are used

as disinfectantsn Effectively kill bacteria and fungi but not endospores

nor nonenveloped virusesn Fast acting, no residue (evaporate away), no stainingn But not very penetrating and no residual activity

(once gone gone)n Exert their action by denaturing proteins and

dissolving lipidsn In tinctures, they enhance the effectiveness of other

antimicrobial chemicalsn Flammable; also may damage rubber, plastic, etc.

A tincture is a nonvolatile substance (medicine) presented as an alcohol solution,

e.g., (for fun with numerous [sic])…

Tinctures

Tinc

ture

Ø “Formulae: Fresh juice of Organic Habanero peppers, New Mexico Jalapeno, African Bird peppers and Hatch Chili peppers.

Ø Dosage: Five to thirty drops, three times daily. CAUTION ~ EXTREMELY HOT!!

Ø Therapeutic Action: Cayenne is the greatest herbal aid to circulation and should be used on a regular basis. The extract is very concentrated and gets into the bloodstream quickly and makes it a perfect first aid remedy for heart attacks, stroke, fainting, shock, dizziness, hemorrhage, internal and external bleeding. Use a few drops to 10 droppers full. It has saved many lives.

Tincture II

Tincture IIn “Formulae: Fresh Garlic Juice, Goldenseal root, Usnea lichen, Myrrh

gum, Pine resin, Echinacea root juice, Tea Tree oil, Kelp, Black Walnut inner hulls, Oak galls and Cayenne pepper in 80% grain alcohol.

n Dosage: Generally for external use but can be used in the oral cavity. Soak a cotton swab in the tincture and scrub into the infected area, let air dry. It has a burning sensation. If the wound is tender, just flush it with multiple droppers full of the tincture but no need to scrub it in.

n Therapeutic Action: There has never been an infected occur when this formula has been used. It's excellent for treating any cut or wound and it is anti-bacterial, anti-viral and anti-fungal. The tree resins in this formula leave an invisible protective, anti-bacterial coating over the wound. This formula was use on a man in England who had the top of his knee torn off in an automobile accident. In 24 hours it literally glued his knee back together. A nurse from Ireland on the scene said in all the years in the hospital, she had never seen such a severe wound close right up and heal, and with no infections.”

Heavy Metalsn Ag, Cu, Hg, Ni, Zn, Ag(NO3)2, CuSO4, ZnCl2,

HgCl2n These metals (and metal ions) react with

sulfhydral (–SH) groups of proteins, denaturing proteins

n Silver nitrate is used to treat Ophthalmianeonatorum in newborns as caused by Neisseria gonorrhoeae

n Oligodynamic action: the ability of very small amounts of heavy metals (especially silver and copper) to exert antimicrobial activity

Heavy Metalsu Include copper, selenium, mercury, silver, and zinc.u Oligodynamic action: Very tiny amounts are effective.A. Silver:u 1% silver nitrate used to protect infants against

gonorrheal eye infections until recently.B. Mercuryu Organic mercury compounds like merthiolate and

mercurochrome are used to disinfect skin wounds.C. Copperu Copper sulfate is used to kill algae in pools and fish

tanks.

Heavy MetalsD. Selenium (硒)u Kills fungi and their spores. Used for fungal

infections.u Also used in dandruff (去頭皮屑) shampoos.E. Zincu Zinc chloride is used in mouthwashes.u Zinc oxide is used as antifungal agent in

paints.

Alkylating agentsn Glutaraldehyde and Formaldehyden Advantages

n Good activity against spores, virues, fungi

n Disdvantagesn Glutaraldehyde only moderately active against TBn Need long exposure time for full effect (3 hours)n freshness & pH criticaln TOXIC!

n Practical usesn Disinfection of endoscopesn Blood spillsn Fumigation

Aldehydesu Include some of the most effective antimicrobials.u Inactivate proteins by forming covalent crosslinks

with several functional groups.A. Formaldehyde gas:u Excellent disinfectant.u Commonly used as formalin, a 37% aqueous

solution.u Formalin was used extensively to preserve biological

specimens and inactivate viruses and bacteria in vaccines.

u Irritates mucous membranes, strong odor.u Also used in mortuaries for embalming.

AldehydesB. Glutaraldehyde:u Less irritating and more effective than formaldehyde.u One of the few chemical disinfectants that is a

sterilizing agent.u A 2% solution of glutaraldehyde (Cidex) is:

u Bactericidal, tuberculocidal, and viricidal in 10 minutes.u Sporicidal in 3 to 10 hours.

u Commonly used to disinfect hospital instruments.u Also used in mortuaries for embalming.

Glutaraldehyde is capable of effectivingsterilization—at room temperature,

even against endospores,and even in the presence of organics,

but achieving sterilization requries many hours of exposure… and it is nasty stuff to

work with!

Glutaraldehyde

Gaseous Chemosterilizersn Propylene oxide (C3H6O)n Chlorine gas (Cl2)n Chlorine dioxide (ClO2)n Ozone (O3)n Ethylene oxide (C2H4O)…

Gaseous Chemosterilizersn to sterilize heat- or moisture-sensitive itemsn for items damaged by heat or moisturen is not corrosive, not damaging to delicate

instruments, microscopes, disposable plastic instruments and materials

n permeates porous materialsn dissipates rapidly from materialn but is costly, toxic, carcinogenic, explosive,

and relatively lengthy process

Gaseous Sterilizersu Chemicals that sterilize in a chamber similar to an

autoclave.u Denature proteins, by replacing functional groups

with alkyl groups.A. Ethylene Oxide:u Kills all microbes and endospores, but requires

exposure of 4 to 18 hours.u Toxic and explosive in pure form.u Highly penetrating.u Most hospitals have ethylene oxide chambers to

sterilize mattresses and large equipment.

Ethylene oxiden Highly toxic flammable gas, kills spores!n Used for bulky items such as heart lung

machinesn Can be used on glutaraldehyde-labile

endoscopesn Use limited by safety issues

Oxidizing Agentsn HOOH, hydrogen peroxide, is most commonn HOOH is not a terribly effective disinfectant or

anticepticn This is because bacteria and body tissues contain

enzymes (catalase) that inactivate hydrogen peroxiden However, the oxygen released upon inactivation can

help oxygenate deep wounds and thus kill strict-anaerobe contaminants, e.g., Clostridium tetani

n Ozone and peracetic acid are also oxidizing antimicrobial agents

n They exert their effect by oxidizing cell macromolecules (e.g., proteins, DNA, etc.)

Peroxygens (Oxidizing Agents)u Oxidize cellular components of treated microbes.u Disrupt membranes and proteins.A. Ozone:u Used along with chlorine to disinfect water.u Helps neutralize unpleasant tastes and odors.u More effective killing agent than chlorine, but less

stable and more expensive.u Highly reactive form of oxygen.u Made by exposing oxygen to electricity or UV light.

Peroxygens (Oxidizing Agents)B. Hydrogen Peroxide:u Used as an antiseptic.u Not good for open wounds because quickly broken

down by catalase present in human cells.u Effective in disinfection of inanimate objects.u Sporicidal at higher temperatures.u Used by food industry and to disinfect contact lenses.C. Benzoyl Peroxide:u Used in acne medications.

Peroxygens (Oxidizing Agents)D. Peracetic Acid:u One of the most effective liquid sporicides

available.u Sterilant :u Kills bacteria and fungi in less than 5 minutes.u Kills endospores and viruses within 30 minutes.

u Used widely in disinfection of food and medical instruments because it does not leave toxic residues.

Efficiency of Different Chemical Antimicrobial Agents

Chemical Antimicrobials

* Type of Disinfectant: H = High level; I = Intermediate level; L = Low level

The Problem of CJD and TSEsn Creutzfeld-Jakob syndrome and other transmissible

spongiform encephalopathies caused by highly resistant proteinaceous particles, prions

n can survive 3 years of environmental exposure and are unusually resistant to conventional decontamination methods

n Iatrogenic CJD documented in three circumstancesn use of contaminated medical equipment (2 cases)n use of extracted pituitary hormones (> 130 cases)n implantation of contaminated grafts from humans (cornea, 3

cases; dura mater, > 110 cases)

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