Physical)and)Chemical)Control) of)microbes) Chapter)9) ) Rela8ve)Resistance)of)Different)Microbial)Types)to) Microbial)Control)Agents) More resistant

Transcription

1 PhysicalandChemicalControl ofmicrobes Chapter9 Rela8veResistanceofMicrobialForms Primary*targets*of*microbialcontrolare*microorganisms* capable*of*causing*infecaon*or*spoilage* Microbes*can*have*extreme*differences*in*resistance*and* harmfulness* Bacterial*endospores*have*tradiAonally*been*considered* the*most*resistant*microbial*enaaes* The*goal*of*any*steriliza8onprocess*is*the*destrucAon*of* bacterial*endospores* - any*process*that*kills*endospores*will*invariably*kill* *other*microbial*forms* Copyright* *The*McGraw3Hill*Companies,*Inc.**Permission*required*for*reproducAon*or*display.* Rela8veResistanceofDifferentMicrobialTypesto MicrobialControlAgents More resistant Prions Bacterial endospores Mycobacterium Staphylococcus and Pseudomonas Protozoan cysts Protozoan trophozoites Most gram-negative bacteria Fungi and fungal spores Nonenveloped viruses ControllingMicroorganisms The*methods*of*microbial*control*used*outside*of*the* body*are*designed*to*result*in*four*possible*outcomes* - steriliza8on(kills*all*microbial*life* - disinfec8on(kills*vegetaave*microbes* - decontamina8on/sani8za8on(cleans*and* *reduces*microbes*on*nonliving*surfaces* - an8sepsis/degerma8on(reduces*microbes*on* *living*assues* Most gram-positive bacteria Less resistant Enveloped viruses

2 ConceptsinAn8microbialControl MicrobialControlMethods Table 9.1 Concepts in Antimicrobial Control Techniques and chemicals that are capable of sterilizing are highlighted with a pink background. Term Defnition Key Points Examples of Agents Sterilization Process that destroys or removes all viable microorganisms (including viruses The term sterile should be used only in the strictest sense to refer to materials that have been subjected to the process of sterilization (there is no such thing as slightly sterile Generally reserved for inanimate objects as it would be impractical or dangerous to sterilize parts of the human body Common uses: surgical instruments, syringes, commercially packaged food Heat (autoclave Sterilants (chemical agents capable of destroying spores Dry Microbial Control Methods Physical agents Chemical agents Mechanical removal methods Heat Radiation Gases Liquids Filtration Moist Sterilization Disinfection Air Liquids Disinfection Decontamination/ Sanitization Antisepsis/ Degermation Physical process or a chemical agent to destroy vegetative pathogens but not bacterial endospores Removes harmful products of microorganisms (toxins from material Cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels Reduces the number of microbes on the human skin A form of decontamination but on living tissues Normally used on inanimate objects because the concentration of disinfectants required to be effective is harmful to human tissue Common uses: boiling food utensils, applying 5% bleach solution to an examining table, immersing thermometers in an iodine solution between uses Important to restaurants, dairies, breweries, and other commercial entities handle large numbers of soiled utensils/containers Common uses: cooking utensils, dishes, bottles, and cans must be sanitized for reuse Involves scrubbing the skin (mechanical friction or immersing it in chemicals (or both Bleach Iodine Heat (boiling Soaps Detergents Commercial dish washers Alcohol Surgical hand scrubs Incineration Dry oven Steam Boiling water, under hot water, Sterilization Sterilization pressure pasteurization Sterilization Disinfection Ionizing X ray, cathode, gamma Sterilization Nonionizing UV Disinfection On animate objects On inanimate objects Antisepsis Disinfection Sterilization Decontamination Sterilization Disinfection: The destruction or removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects. Sterilization: The complete removal or destruction of all viable microorganisms. Used on inanimate objects. Antisepsis/Degermation: Chemicals applied to body surfaces to destroy or inhibit vegetative pathogens. Decontamination/Sanitization: The mechanical removal of most microbes. MeansofMicrobialControl Ccidalagents*can*kill*their*target* Bacteriocide:**chemical*that*destroys*bacteria* (except*for*endospores* Fungicide,virucide,sporicide,germicide/ microbicide* Stasis*and*sta8c*mean* to*stand*sall Bacteriosta8c:chemical*agents*that*prevent*the* growth*of*bacteria*on*assues*or*on*objects*in*the* environment* AnAsepAcs*and*drugs*oKen*have*microbista8c*effects* because*microbicidal*compounds*can*be*toxic*to*human* cells* MeansofMicrobialControl Sepsis:**the*growth*of*microorganisms*in*the*blood*and* other*assues* Asepsis:absence*of*significant*contaminaAon* - asep8ctechniques:**pracaced*in*healthcare* - any*pracace*that*prevents*the*entry*of* *infecaous*agents*into*sterile*assues** - range*from*sterile*methods*to*use*of*an8sep8c treatments* An8sep8cs:**chemical*agents*applied*directly*to* exposed*body*surfaces*(skin*and*mucous*membranes,* wounds,*and*surgical*incisions*to*prevent*vegetaave* pathogens* iodine*compounds,*hydrogen*peroxide,*alcohol* swabs,*germicidal*soap*

3 Prac8calMaIersinMicrobialControl Does*the*applicaAon*require*sterilizaAon,*or*is*disinfecAon* adequate?* Is*the*item*to*be*reused*or*permanently*discarded?* If*it*will*be*reused,*can*the*item*withstand*heat,*pressure,* radiaaon,*or*chemicals?* Is*the*control*method*appropriate*for*a*given*applicaAon?* Will*a*chemical*leave*an*undesirable*residue?* WhatIsMicrobialDeath? Death:* - microbes*have*no*conspicuous*vital*processes,* *therefore*death*is*difficult*to*determine* - permanent*loss*of*reproducave*capability*has* *become*the*accepted*microbiological*definiaon* *of*death* Will*the*agent*penetrate*to*the*necessary*extent?* Is*the*method*cost3*and*labor3efficient*and*is*it*safe?* FactorsAffec8ngDeathRate Death*of*the*whole*populaAon*is*not*instantaneous* - begins*when*a*certain*threshold*of*microbicidal* *agent*is*met* - death*conanues*in*a*logarithmic*manner*as*the* *Ame*or*concentraAon*is*increased* - acave*cells*tend*to*die*more*quickly*than*less* *metabolically*acave*cells* FactorsAffec8ngDeathRate The*number*of*microbes* The*type*of*microorganisms* Temperature*and*pH*of*the*environment* The*presence*of*solvents,*interfering*organic*maTer,* and*inhibitors* - saliva,*blood,*and*feces*can*inhibit*the*acaon* *of*disinfectants*and*even*the*acaon*of*heat* - Eventually,*a*point*is*reached*at*which*survival*of* *any*cells*is*highly*unlikely;*this*point*is* *equivalent*to*sterilizaaon*

4 ModesofAc8onofAn8microbialAgents AnAmicrobials*have*a*range*of*cellular*targets* - least*selecave*agents*tend*to*be*effecave* *against*the*widest*range*of*microbes*(heat*and* *radiaaon* - selecave*agents*target*only*a*single*cellular* *component*(drugs* Ac8onsofVariousPhysicalandChemicalAgents UpontheCell Table 9.3 Actions of Various Physical and Chemical Agents upon the Cell Cellular Target Cell Wall Cell Membrane Cellular Synthesis Proteins Effects of Agents Chemical agents can damage the cell wall by: Blocking its synthesis Digesting the cell wall Agents physically bind to lipid layer of the cell membrane, opening up the cell membrane and allowing injurious chemicals to enter the cell and important ions to exit the cell. Agents can interrupt the synthesis of proteins via the ribosomes, inhibiting proteins needed for growth and metabolism and preventing multiplication. Agents can damage DNA. Some agents are capable of denaturing proteins (breaking of protein bonds, which results in breakdown of the protein structure. Agents may attach to the active site of a protein, preventing it from interacting with its chemical substrate. Examples of Agents Used Chemicals Detergents Alcohol Detergents Formaldehyde Radiation Ethylene oxide Moist heat Alcohol Phenolics ModeofAc8onofSurfactantsontheCellMembrane Cytoplasm Surfactant molecules Membrane phospholipids ConceptCheck The*use*of*iodine*compounds*to*prepare*the*skin*for* surgery*is*known*as* * A. disinfecaon.* B. anasepsis.* C. sterilizaaon.* D. decontaminaaon.* E. iodinaaon.*

5 MethodsofPhysicalControl:Heat Elevated*temperatures*are*microbicidal* ComparisonofTimesandTemperaturestoAchieve Steriliza8onwithMoistandDryHeat Lower*temperatures*are*microbistaAc* Moistheat:**hot*water,*boiling*water,*or*steam* - between*60 C*and*135 C* Dryheat:**hot*air*or*an*open*flame* - ranges*from*160 C*to*thousands*of*degrees* *Celsius* Moist*heat*is*more*effecAve*at*microbial*control* HeatResistanceandThermalDeath: SporesandVegeta8veCells Bacterial*endospores* - exhibit*greatest*resistance* - destrucaon*of*spores*usually*requires* *temperatures*above*boiling** * VegetaAve*cells* - death*ames*vary*from*50 C*for*3*minutes*to* *60 C*for*60*minutes* HeatResistanceandThermalDeath: SporesandVegeta8veCells(cont d VegetaAve*cells*of*sporeformers*have*the*same* suscepability*to*heat*as*vegetaave*cells*of*non3 sporeformers* Pathogens*have*the*same*suscepAbility*to*heat*as* nonpathogens* Fungi,*protozoa,*and*worms*are*similar*in*their* sensiavity*to*heat* Viruses*can*be*resistant*to*heat* - tolerance*extends*from*55 C*for*2* *5*minutes*to* *60 C*for*600*minutes*

6 Suscep8bilityofMicrobestoHeat: ThermalDeathMeasurements MoistHeatMethods Table 9.5 Moist Heat Methods Techniques and chemicals that are capable of sterilizing are highlighted with a pink background. Thermaldeath8me(TDT:shortest*length*of*Ame* required*to*kill*all*test*microbes*at*a*specified* temperature* Method Thermaldeathpoint(TDP:the*lowest*temperature* required*to*kill*all*microbes*in*a*sample*in*10*minutes* Applications Boiling Water: Disinfection A simple boiling water bath or chamber can quickly decontaminate items in the clinic and home. Because a single processing at 100 C will not kill all resistant cells, this method can be relied on only for disinfection and not for sterilization. Exposing materials to boiling water for 30 minutes will kill most nonspore-forming pathogens, including resistant species such as the tubercle bacillus and staphylococci. Probably the greatest disadvantage with this method is that the items can be easily recontaminated when removed from the water. Useful in the home for disinfection of water, materials for babies, food and utensils, bedding, and clothing from the sickroom Pasteurization: Disinfection of Beverages 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 and destroy pathogens. 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 food value. Milk, wine, beer, other beverages Ordinary pasteurization techniques require special heat exchangers that expose the liquid to 71.6 C for 15 seconds (flash method or to 63 C to 66 C for 30 minutes (batch method. The first method is preferable because it is less likely to change flavor and nutrient content, and it is more effective against certain resistant pathogens such as Coxiella and Mycobacterium. Although these treatments inactivate most viruses and destroy the vegetative stages of 97% to 99% of bacteria and fungi, they do not kill endospores or particularly heat-resistant microbes (mostly nonpathogenic lactobacilli, micrococci, and yeasts. Milk is not sterile after regular pasteurization. In fact, it can contain 20,000 microbes per milliliter or more, which explains why even an unopened carton of milk will eventually spoil. (Newer techniques can also produce sterile milk that has a storage life of 3 months. This milk is processed with ultrahigh temperature [UHT] 134 C for 1 to 2 seconds. This is not generally considered pasteurization, so we don t consider pasteurization a sterilization method. Heat*treatment*of*perishable*substances*must**render* the*product*free*of*agents*of*spoilage*or*disease*with* acceptable*speed*and*cost*of*processing* Monday Tuesday Wednesday Nonpressurized Steam Selected substances that cannot withstand the high temperature of the autoclave can be subjected to intermittent sterilization, also called tyndallization. This technique requires a chamber to hold the materials and a reservoir for boiling water. Items in the chamber are exposed to free-flowing steam for 30 to 60 minutes. This temperature is not sufficient to reliably kill spores, so a single exposure will not suffice. On the assumption that surviving spores will germinate into less resistant vegetative cells, the items are incubated at appropriate temperatures for 23 to 24 hours, and then again subjected to steam treatment. This cycle is repeated for 3 days in a row. Because the temperature never gets above 100 C, highly resistant spores that do not germinate may survive even after 3 days of this treatment. Heat-sensitive culture media, such as those containing sera, egg, or carbohydrates (which can break down at higher temperatures and some canned foods. Probably not effective in sterilizing items such as instruments and dressings that provide no environment for spore germination, but it certainly can disinfect them. Thursday Friday Even though this is sometimes called intermittent sterilization, sterilization is not guaranteed so we don t consider it a reliable sterilization method. (pot: The McGraw-Hill companies, Inc./Charles D. Winters, photographer; (pasteurization: James King-Holmes/Photo Researchers; (beer: John A. Rizzo/Getty Images (RF; MoistHeatMethods DryHeatMethods Table 9.5 (continued Table 9.6 Dry Heat Methods Techniques and chemicals that are capable of sterilizing are highlighted with a pink background. Applications Method Steam Under Pressure: Sterilization At sea level, normal atmospheric pressure is 15 pounds per square inch (psi, or 1 atmosphere. At this pressure, water will boil (change from a liquid to a gas at 100 C, and the resultant steam will remain at exactly that temperature, which is unfortunately too low to reliably kill all microbes. In order to raise the temperature of steam, the pressure at which it is generated must be increased. As the pressure is increased, the temperature at which water boils and the temperature of the steam produced both rise. For example, at a pressure of 20 psi (5 psi above normal, the temperature of steam is 109 C. As the pressure is increased to 10 psi above normal, the steam s temperature rises to 115 C, and at 15 psi above normal (a total of 2 atmospheres, it will be 121 C. It is not the pressure by itself that is killing microbes but the increased temperature it produces. Heat-resistant materials such as glassware, cloth (surgical dressings, metallic instruments, liquids, paper, some media, and some heatresistant plastics. If items are heat-sensitive (plastic Petri dishes but will be discarded, the autoclave is still a good choice. However, it is ineffective for sterilizing substances that repel moisture (oils, waxes, or for those that are harmed by it (powders. Such pressure-temperature combinations can be achieved only with a special device that can subject pure steam to pressures greater than 1 atmosphere. Health and commercial industries use an autoclave for this purpose, and a comparable home appliance is the pressure cooker. The most efficient pressure-temperature combination for achieving sterilization is 15 psi, which yields 121 C. It is important to avoid overpacking or haphazardly loading the chamber, which prevents steam from circulating freely around the contents and impedes the full contact that is necessary. The duration of the process is adjusted according to the bulkiness of the items in the load (thick bundles of material or large flasks of liquid and how full the chamber is. The range of holding times varies from 10 minutes for light loads to 40 minutes for heavy or bulky ones; the average time is 20 minutes. Pressure regulator Recorder Safety valve Exhaust to atmosphere Steam from jacket to chamber or exhaust from chamber Control handle Steam to jacket Door gasket Steam from jacket to chamber Jacket condensate return Strainer Discharge Steam jacket Steam supply Steam supply valve Temperaturesensing bulb Trap Applications Method Incineration in a flame is perhaps the most rigorous of all heat treatments. The flame of a Bunsen burner reaches 1,870 C at its hottest point, and furnaces/incinerators operate at temperatures of 800 C to 6,500 C. Direct exposure to such intense heat ignites and reduces microbes and other substances to ashes and gas. Bunsen burners/small incinerators: laboratory instruments such as inoculating loops. Large incinerators: syringes, needles, culture materials, dressings, bandages, bedding, animal carcasses, and pathology samples. Incineration of microbial samples on inoculating loops and needles using a Bunsen burner is a very common practice in the microbiology laboratory. This method is fast and effective, but it is also limited to metals and heatresistant glass materials. This method also presents hazards to the operator (an open flame and to the environment (contaminants on needle or loop often spatter when placed in flame. Tabletop infrared incinerators have replaced Bunsen burners in many labs for these reasons. Large incinerators are regularly employed in hospitals and research labs for complete destruction of infectious materials. The hot-air oven provides another means of dry-heat sterilization. The so-called dry oven is usually electric (occasionally gas and has coils that radiate heat within an enclosed compartment. Heated, circulated air transfers its heat to the materials in the oven. Sterilization requires exposure to 150 C to 180 C for 2 to 4 hours, which ensures thorough heating of the objects and destruction of endospores. Glassware, metallic instruments, powders, and oils that steam does not penetrate well. Not Suitable for plastics, cotton, and paper, which may burn at the high temperatures, or for liquids, which will evaporate. Condensate to waste Steam trap (autoclave: Science VU/Visuals Unlimited (top: Raymond B. Otero/Visuals Unlimited; (bottom: Steve Allen/Brand X Pictures (RF

7 TheEffectsofColdandDesicca8on Principal*benefit*of*cold*treatment*is*to*slow*growth*of* microbes* * Most*microbes*are*not*killed*by*gradual*cooling,*long3 term*refrigeraaon,*or*deep3freezing* Temperatures*from*370 C*to*3135 C*can*preserve* cultures*of*bacteria,*viruses,*and*fungi*for*long*periods* Psychrophiles*grow*slowly*at*freezing*temperatures* and*can*secrete*toxic*products* TheEffectsofColdandDesicca8on Desicca8on:**vegetaAve*cells*directly*exposed*to* normal*room*temperature*gradually*become* dehydrated* - Streptococcus*pneumoniae,*the*spirochete*of* *syphilis,*and*neisseria*gonorrhoeae*die*aker*a* *few*hours*of*air*drying* - endospores*of*bacillus*and*clostridium*are*viable* *for**thousands*of*years*under*extremely*arid* *condiaons* - staphylococci,*staphylococci,*and*the*tubercle* *bacillus*remain*viable*in*air*and*dust* - many*viruses*and*fungi*can*also*withstand*long* *periods*of*desiccaaon* TheEffectsofColdandDesicca8on Lyophiliza8on - combinaaon*of*freezing*and*drying* - method*of*preserving*microorganisms*in*a* *viable*state*for*many*years* - pure*cultures*are*frozen*instantaneously*and* *exposed*to*a*vacuum*that*removes*water,* *avoiding*the*formaaon*of*ice*crystals Radia8on Ionizing*RadiaAon* - gamma*rays,*x*rays,*high*energy*electron*beams* - damages*dna* - can*sterilize* - food*processing,*medical*supplies,*mail* Nonionizing*RadiaAon* - ultraviolet*(uv*radiaaon* most*effecave*at*260*nm* - damages*dna*(thymine*dimers* - can*disinfect*vaccines* - germicidal*lamps*in*hospitals,*nurseries,* *cafeterias* - must*be*directly*exposed*to*uv*rays* - can*damage*eyes*and*skin*

8 OtherPhysicalMethods:Filtra8on EffecAve*method*to*remove*microbes*from*air**and* liquids* - fluid*is*strained*through*a*filter*with*openings* *large*enough*for*the*fluid*to*pass,*too*small*for* *microbes* - thin*membranes*of*cellulose*acetate,* *polycarbonate,*and*plasacs*whose*pore*size* *is*carefully*controlled* - charcoal,*diatomaceous*earth,*or*unglazed* *porcelain*are*also*used* - pore*sizes*can*be*controlled*to*permit*true* *sterilizaaon*by*trapping*viruses* Filtra8on Used*to*prepare*liquids*that*cannot*withstand*heat* - serum,*blood*products,*vaccines,*drugs,*iv* *fluids,*enzymes,*and*media* AlternaAve*method*for*decontaminaAng*beverages* without*altering*flavor* Important*step*in*water*purificaAon* Unable*to*remove*soluble*molecules*(toxins*that*can* cause*disease* Efficient*means*of*removing*airborne*contaminants* - high*efficiency*paraculate*air*(hepa*filters*are* *used*in*hospital*rooms*and*sterile*rooms* MembraneFiltra8on Osmo8cPressure Adding*large*amounts*of*salt*or*sugar*to*foods*creates*a* hypertonic*environment*for*bacteria,*causing* plasmolysis* Liquid Filter Pore Pickling,*smoking,*and*drying*foods*have*been*used*for* centuries*to*preserve*foods* OsmoAc*pressure*is*never*a*sterilizing*technique* Filter Sterilized fluid (b Vacuum pump suction (a Fred Hossler/Visuals Unlimited

9 ChemicalAgentsinMicrobialControl * Range*from*disinfectants*and*anAsepAcs*to*sterilants* and*preservaaves* Aqueoussolu8ons:**chemicals*dissolved*in*pure*water* Tinctures:chemicals*dissolved*in*pure*alcohol**or* water3alcohol*mixtures Selec8ngaMicrobicidalChemical Rapid*acAon* Solubility*and*long3term*stability* Broad3spectrum*acAon* Nontoxic*to*human*and*animal*Assues* PenetraAon*of*inanimate*surfaces* Resistance*to*becoming*inacAvated*by*organic*maTer* Noncorrosive/nonstaining* SaniAzing/deodorizing* Affordable*and*readily*available* Nochemicalcancompletelyfulfillallofthese requirements - glutaraldehyde*and*hydrogen*peroxide* *approach*this*ideal* Selec8ngaMicrobicidalChemical Germicides*are*evaluated*in*terms*of*their* effecaveness*in*destroying*microbes*in*medical**and* dental*sejngs* - high3level*germicides*kill*endospores*and*can*be* *used*as*sterilants - intermediate3level*germicides*kill*fungal,*but* *not*bacterial*spores,*resistant*pathogens,*and* *viruses* - low3level*germicides*eliminate*only*vegetaave* *bacteria,*vegetaave*fungal*cells,*and*some* *viruses* FactorsAffec8ngtheGermicidalAc8vityof Chemicals Nature*of*the*microorganisms*being*treated* Nature*of*the*material*being*treated* Degree*of*contaminaAon* Time*of*exposure* Strength*of*chemical*acAon*of*the*germicide* Chemical*concentraAon*

10 FactorsAffec8ngtheGermicidalAc8vityof Chemicals Length*of*Exposure - Most*compounds*require*adequate*contact*Ame* *to*allow*the*chemical*to*penetrate*and*act*on* *microbes*present* RequiredConcentra8onsandTimesforChemical Destruc8onofSelectedMicrobes ComposiAon*of*material*being*treated* - smooth,*solid*objects*are*more*reliably* *disinfected*than*those*with*pores*or*pockets* - large*amounts*of*organic*material*can*hinder* *penetraaon* - adequate*cleaning*of*instruments*and*other* *reusable*materials*must*precede*the*use*of*a* *germicide*or*sterilant*** GermicidalCategoriesAccordingto ChemicalGroup SterilizingAgents Table 9.9 Germicidal Categories According to Chemical Group Techniques and chemicals that are capable of sterilizing are highlighted with a pink background. Agent Halogens: chlorine Halogens: iodine Hydrogen peroxide (H 2O 2 Aldehydes Gaseous sterilants/ disinfectants Target Microbes Can kill spores (slowly; all other microbes Can kill spores (slowly; all other microbes Kills spores and all other microbes Kill spores and all other microbes Ethylene oxide kills spores; other gases less effective Form(s Liquid/gaseous chlorine (Cl 2, hypochlorites (OCl, chloramines (NH 2Cl Free iodine in solution (I 2 Iodophors (complexes of iodine and alcohol Colorless, caustic liquid Decomposes in the presence of light metals or catalase into water, and oxygen gas Organic substances bearing a CHO functional group on the terminal carbon Ethylene oxide is a colorless substance that exists as a gas at room temperature Mode of Action In solution, these compounds combine with water and release hypochlorous acid (HOCl; denature enzymes permanently and suspend metabolic reactions Penetrates cells of microorganisms where it interferes with a variety of metabolic functions; interferes with the hydrogen and disulfide bonding of proteins Oxygen forms free radicals ( OH, which are highly toxic and reactive to cells Glutaraldehyde can irreversibly disrupt the activity of enzymes and other proteins within the cell Formaldehyde is a sharp irritating gas that readily dissolves in water to form an aqueous solution called formalin; attaches to nucleic acids and functional groups of amino acids Ethylene oxide reacts vigorously with functional groups of DNA and proteins, blocking both DNA replication and enzymatic actions Chlorine dioxide is a strong alkylating agent Indications for Use Limitations Chlorine kills bacteria, Less effective if exposed to endospores, fungi, and viruses; light, alkaline ph and gaseous/ liquid chlorine: used excess organic matter todisinfect drinking water, sewage and waste water; hypochlorites: used in health care to treat wounds, disinfect bedding and instruments, sanitize food equipment and in restaurants, pools and spas; chloramines: alternative to pure chlorine in treating drinking water; also used to treat wounds and skin surfaces 2% iodine, 2.4% sodium iodide Can be extremely irritating (aqueous iodine is used as a to the skin and is toxic topical antiseptic when absorbed 5% iodine, 10% potassium iodide used as a disinfectant for plastic and rubber instruments, cutting blades, etc. Iodophor products contain 2% to 10% of available iodine, which is released slowly; used to prepare skin for surgery, in surgical scrubs, to treat burns, and as a disinfectant As an antiseptic, 3% hydrogen Sporicidal only in high peroxide is used for skin and concentrations wound cleansing, mouth washing, bedsore care Used to treat infections caused by anaerobic bacteria 35% hydrogen peroxide is used in low temperature sterilizing cabinets for delicate instruments Glutaraldehyde kills rapidly Glutaraldehyde is and is broad-spectrum; somewhat unstable, used to sterilize respiratory especially with increased equipment, scopes, kidney ph and temperature dialysis machines, dental Formaldehyde is extremely instruments toxic and is irritating Formaldehyde kills more slowly to skin and mucous than glutaraldehyde; used to membranes disinfect surgical instruments Ethylene oxide is used to Ethylene oxide is disinfect plastic materials and explosive it must delicate instruments; can also be combined with a high be used to sterilize syringes, percentage of carbon surgical supplies, and medical dioxide or fluorocarbon devices that are prepackaged It can damage lungs, eyes, and mucous membranes if contacted directly Ethylene oxide is rated as a carcinogen by the government GermicidalCategoriesAccordingto ChemicalGroup Disinfec8onOnly Table 9.9 (continued Agent Phenol (carbolic acid Chlorhexidine Alcohol Detergents Heavy metal compounds Target Microbes Some bacteria, viruses, fungi Most bacteria, viruses, fungi Most bacteria, viruses, fungi Some bacteria, viruses, fungi Some bacteria, viruses, fungi Form(s Derived from the distillation of coal tar Phenols consist of one or more aromatic carbon rings with added functional groups Complex organic base containing chlorine and two phenolic rings Colorless hydrocarbons with one or more OH functional groups Ethyl and isopropyl alcohol are suitable for antimicrobial control Polar molecules that act as surfactants Anionic detergents have limited microbial power Cationic detergents, such as quaternary ammonium compounds ( quats, are much more effective antimicrobials Heavy metal germicides contain either an inorganic or an organic metallic salt; may come in tinctures, soaps, ointment, or aqueous solution Mode of Action Indications for Use Limitations In high concentrations they are cellular poisons, disrupting cell walls and membranes, proteins In lower concentrations they inactivate certain critical enzyme systems Targets both bacterial membranes, where selective permeability is lost, and proteins, resulting in denaturation Concentrations of 50% and higher dissolve membrane lipids, disrupt cell surface tension and compromise membrane integrity Positively charged end of the molecule binds well with the predominantly negatively charged bacterial surface proteins Long, uncharged hydrocarbon chain allows the detergent to disrupt the cell membrane Cell membrane loses selective permeability, causing cell death Mercury, silver, and other metals exert microbial effects by binding onto functional groups of proteins and inactivating them Phenol remains one standard against which other (less toxic phenolic disinfectants are rated; the phenol coefficient quantitatively compares a chemical s antimicrobial properties to those of phenol Phenol is now used only in certain limited cases, such as in drains, cesspools, and animal quarters Mildness, low toxicity and rapid action make chlorhexidine a popular choice of agents Used in hand scrubs, prepping skin for surgery, as an obstetric antiseptic, as a mucous membrane irrigant, etc. Germicidal, nonirritating, and inexpensive Routinely used as skin degerming agents (70% to 95% solutions Effective against viruses, algae, fungi, and gram-positive bacteria Rated only for low-level disinfection in the clinical setting Used to clean restaurant utensils, dairy equipment, equipment surfaces, restrooms Organic mercury tinctures are fairly effective antiseptics Organic mercurials serve as preservatives in cosmetics, ophthalmic solutions, and other substances Silver nitrate solutions are used for topical germicides and ointments Toxicity of many phenolics makes them dangerous to use as antiseptics Effects on viruses and fungi are variable Rate of evaporation decreases effectiveness Inhalation of vapors can affect the nervous system Ineffective against tuberculosis bacterium, hepatitis virus, Pseudomonas, and spores Activity is greatly reduced in presence of organic matter Detergents function best in alkaline solutions Microbes can develop resistance to metals Not effective against endospores Can be toxic if inhaled, ingested, or absorbed May cause allergic reactions in susceptible individuals (top: Richard Hutchings (RF; (Bottom: The McGraw-Hill Companies, Inc./Jill Braaten, photographer (alcohol: Richard Hutchings (RF; (heavy metal: The McGraw-Hill Companies, Inc./Stephen Frisch, photographer

11 OtherAn8microbialAgents Acids*and*Alkalis* - very*low*or*very*high*ph*can*destroy*or*inhibit* microbial*cells* Ac8veIngredientsofVariousCommercial An8microbialProducts - limited*in*applicaaons*due*to*their*corrosive,* causac,*and*hazardous*nature* - ammonium*hydroxide*used*in*detergents,*cleaners,* and*deodorizers* - organic*acids*used*in*food*preservaaon* ConceptCheck Which*of*the*following*anAmicrobial*chemicals*are* considered*sterilizing*agents?* * A. chlorhexidine* B. hydrogen*peroxide*(h 2 O 2 * C. alcohol* D. aceac*acid* E. None*of*the*choices*is*correct.*