Chap 9 – BYU – Flashcards
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| Sterilization |
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| The complete absence of life |
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| Disinfection |
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| Destruction of vegetative pathogens; usually on inanimate objects |
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| -cides |
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| Agents which kill |
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| -static |
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| Agents which prevent growth |
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| Sepsis |
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| Bacterial contamination & growth |
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| Antiseptic |
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| Agent which destroys vegetative pathogens; usually on living tissue |
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| Sanitation |
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| Lowering bacterial counts to safe public health levels |
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| Heat |
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| • Microbiologists normally use log reduction to represent microbial kill. Most manufacturers of disinfectants speak in terms of percent kill. |
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| D value |
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| Time required to kill 90% (1 log) at a specific temperature. |
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| Moist heat under pressure |
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| steam autoclave (121 ?C for 20 min) |
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| Moist heat not under pressure |
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| pasteurization (63 ?C for 30 min or 72 ?C for 15 sec) |
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| Dry heat |
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| oven (170 ?C for 2 hrs) |
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| Heat and chemical vapor |
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| Chemiclave (132 ?C for 20 min using 15 psi of alcohol/formaldehyde vapor) |
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| Action of Antimicrobial Agents |
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| • Many types of chemical and physical microbial controls • Modes of action fall into two basic categories – Alteration of cell walls or cytoplasmic membranes – Interference with protein and nucleic acid structure |
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| Alteration of Cell Walls and Membranes |
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| • Cell wall maintains integrity of cell – When disrupted, cannot prevent cell from bursting due to osmotic effects • Cytoplasmic membrane contains cytoplasm and controls passage of chemicals into and out of cell – When damaged, cellular contents leak out • Viral envelope responsible for attachment of virus to target cell – Damage to envelope interrupts viral attachment • Nonenveloped viruses have greater tolerance of environmental insults |
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| Damage to Proteins and Nucleic Acids |
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| • Protein function depends on 3-D shape – Extreme heat or certain chemicals denature proteins • Chemicals, radiation, and heat can alter or destroy nucleic acids – Can produce fatal mutants – Can halt protein synthesis through action on RNA |
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| Selection of Microbial Control Methods |
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| • Ideally, agents should be: – Inexpensive – Fast-acting – Stable during storage – Control all microbial growth while being harmless to humans, animals, and objects |
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| Factors Affecting Disinfectant Action |
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| • Contact Time: Longer, the more effective • Temperature: Higher, the more effective • pH: depends on chemical; some synergy • Bioburden: More microbes = longer time • Types of Microbes: Mycobacteria & spores • Extraneous matter: Organic matter inhibits • Proper Exposure: Insure agent gets in • Disinfectant concentration: Higher = better – exception with the alcohols |
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| Site to Be Treated |
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| • Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects • Method and level of microbial control based on site of medical procedure: – Critical instruments – Semi-critical instruments – Non-critical instruments |
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| Methods for Evaluating Disinfectants and Antiseptics |
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| • Phenol Coefficient - Outdated • Use-Dilution Test - AOAC • Suspension Tests – Log reductions • In-Use Tests – Samples taken before and after disinfection |
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| The AOAC Use-Dilution Test: |
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| • Coat steel cylinders with dried bacteria: |
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| Coat steel cylinders with dried bacteria: |
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| – Staphylococcus aureus – Pseudomonas aeruginosa – Salmonella choleraesuis |
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| The AOAC Use-Dilution Test: Physical Methods of Microbial Control |
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| • Exposure to extremes of heat • Exposure to extremes of cold • Desiccation • Filtration • Osmotic pressure • Radiation |
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| Heat-Related Methods |
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| • Effects of high temperatures – Denaturation of proteins – Interference with integrity of cytoplasmic membrane and cell walls – Disruption of structure and function of nucleic acids |
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| Moist Heat |
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| • Used to disinfect, sanitize, and sterilize • Kills by denaturing proteins and destroying cytoplasmic membranes • More effective than dry heat; water better conductor of heat than air • Methods of microbial control using moist heat – Boiling – Autoclaving – Pasteurization – Ultrahigh-Temperature Sterilization |
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| Boiling |
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| • Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and viruses within 10 minutes at sea level • Temperature cannot exceed 100?C at sea level; steam carries heat away • Boiling time is critical • Water boils at lower temperatures at higher elevations; requires longer boiling time • Endospores protozoan cysts, and prions can survive boiling |
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| Autoclaving |
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| • Pressure applied to boiling water prevents steam from escaping • Boiling temperature increases as pressure increases • Autoclave conditions = 121?C, 15 psi, 15 minutes |
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| Pasteurization |
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| • Pasteur’s method • Today, also used for milk, ice cream, yogurt, and fruit juices • Not sterilization; heat-tolerant and heat-loving microbes survive – These do not cause spoilage prior to consumption – These are generally not pathogenic |
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| Pasteurization Dry Heat |
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| • Used for materials that cannot be sterilized with or are damaged by moist heat • Denatures proteins and oxidizes metabolic and structural chemicals • Requires higher temperatures for longer time than moist heat (106?C for 2 hr or 171?C for 1 hr) • Incineration – ultimate means of sterilization |
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| Refrigeration and Freezing |
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| • Decrease microbial metabolism, growth, and reproduction – Chemical reactions occur slower at low temps – Liquid water not available when frozen • Psychrophilic microbes can multiply in refrigerated foods • Refrigeration halts growth of most pathogens • Slow freezing more effective than quick freezing • Organisms vary in susceptibility to destruction by freezing |
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| Desiccation and Lyophilization |
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| • Drying inhibits growth due to removal of water; only microbiostatic • Lyophilization used for long term preservation of microbial cultures – Prevents formation of damaging ice crystals |
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| Membrane Filtration Osmotic Pressure |
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| • High concentrations of salt or sugar in foods to inhibit growth • Water in cell is drawn out by osmosis; cell desiccates • Fungi have greater ability than bacteria to survive hypertonic environments |
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| Radiation |
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| • Shorter wavelength equals more energy and greater penetration • Radiation described as ionizing or nonionizing according to effects on cellular chemicals |
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| Ionizing Radiation |
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| • Wavelengths shorter than 1 nm – electron beams, gamma rays, and X- rays • Create ions by ejecting electrons from atoms they strike • Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxide ions; hydroxide ions denature other molecules (DNA) • Causes double-stranded breaks in DNA |
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| Ionizing Radiation |
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| • Electron beams – effective at killing but do not penetrate well – Used to sterilize some sliced meats, microbiological plastic ware, and medical and dental supplies • Gamma rays – penetrate well but require hours to kill microbes – Used to sterilize meats, spices, and fresh fruits and vegetables • X-rays require too much time to be practical for growth control |
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| Nonionizing Radiation |
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| • Wavelengths greater than 1 nm • Excites electrons and causes them to make new covalent bonds – Affects 3-D structure of proteins and nucleic acids • UV light causes thymine dimers in DNA • UV light does not penetrate well • Suitable for disinfecting air, transparent fluids, and surfaces of objects |
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| Chemical Methods of Microbial Control |
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| • Affect microbes’ cell walls, cytoplasmic membranes, proteins, or DNA • Effect varies with temperature, length of exposure, and amount of organic matter • Also varies with pH, concentration, and age of chemical • Tend to be more effective against enveloped viruses and vegetative cells of bacteria, fungi, and protozoa |
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| Chemical Methods of Microbial Control |
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| • Major Categories – Phenols – Alcohols – Halogens – Oxidizing agents – Surfactants – Heavy Metals – Aldehydes – Gaseous Agents – Antimicrobics |
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| Some Representative Disinfectants: Phenol and Phenolics |
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| • Intermediate- to low-level disinfectants • Denature proteins and disrupt cell membranes • Effective in presence of organic matter and remain active for prolonged time • Commonly used in health care settings, labs, and homes (Lysol, triclosan) • Have disagreeable odor and possible side effects |
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| Alcohols |
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| • Intermediate-level disinfectants • Denature proteins and disrupt cytoplasmic membranes • Evaporate rapidly – both advantageous and disadvantageous • Swabbing of skin with 70% ethanol prior to injection • Good surface disinfectants; resistant to inactivation by organic compounds |
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| Halogens |
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| • Intermediate-level antimicrobial chemicals • Believed that they damage enzymes via oxidation or by denaturing them • Iodine tablets, iodophores (Betadine®), chlorine treatment of drinking water, bleach, chloramines in wound dressings, and bromine disinfection of hot tubs |
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| Oxidizing Agents |
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| • Peroxides, ozone, and peracetic acid kill by oxidation of microbial enzymes • High-level disinfectants and antiseptics • Hydrogen peroxide can disinfect and sterilize surfaces of objects – Catalase neutralizes; not real useful for treating open wounds • Ozone treatment of drinking water • Peracetic acid – effective sporicide used to sterilize equipment |
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| Surfactants |
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| • “Surface active” chemicals that reduce surface tension of solvents to make them more effective at dissolving solutes • Soaps and detergents – Soaps have hydrophilic and hydrophobic ends; good degerming agents but not antimicrobial – Detergents are positively charged organic surfactants • Quats – colorless, tasteless, harmless to humans, and antimicrobial; ideal for many medical and industrial application – Low-level disinfectants |
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| Quaternary Ammonium Compounds (Quats) Heavy Metals |
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| • Ions are antimicrobial because they alter the 3-D shape of proteins, inhibiting or eliminating their function • Low-level bacteriostatic and fungistatic agents • 1% silver nitrate to prevent blindness caused by N. gonorrhoeae • Thimerosal used to preserve vaccines • Copper controls algal growth in reservoirs, fish tanks, swimming pools, and water storage tanks; interferes with chlorophyll |
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| Aldehydes |
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| • Compounds containing terminal –CHO groups • Cross-link with amino, hydroxyl, sulfhydryl, and carboxyl groups to denature proteins and inactivate nucleic acids • Glutaraldehyde both disinfects (short exposure) and sterilizes (long exposure) • Formalin used in embalming and disinfection of rooms and instruments |
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| Gaseous Agents |
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| • Ethylene oxide, propylene oxide, and beta-propiolactone used in closed chambers to sterilize items • Denature proteins and DNA by cross-linking functional groups • Used in hospitals and dental offices • Can be hazardous to people, often highly explosive, extremely poisonous, and are potentially carcinogenic |
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| Development of Resistant Microbes |
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| • It is unknown whether extensive use of products containing antibacterial chemicals adds to human or animal health • The use of such products does not promote the development of antibiotic resistant microbes |
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| Microbes in the Air (Aerobiology) |
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| • Microbes have different residence times in the air dependent upon the particles on which they are riding • Barrier HEPA filters in biological safety cabinets and operating rooms • Air Sampling devices – The Anderson sampler mirrors the human respiratory system |
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| Eliminating Hands as Vehicles of Disease Transmission |
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| • Gloves • Antimicrobial hand treatments |
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| Summary of Infection Control Best Agents for Specific Situations |
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| Antimicrobial Handwash 4% chlorhexidine Countertop Disinfection 70-80% ethanol Large Area Disinfection Substituted (floor mop water) Phenols Semicritical Instrument 2% - 3.2% Disinfection glutaraldehyde Sterilization of Plastics Gamma irradiation Sterilization of scopes H2O2 gas plasma |
