Term
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Definition
| The complete absence of life |
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Term
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Definition
| Destruction of vegetative pathogens; usually on inanimate objects |
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Definition
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Term
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Definition
| Agents which prevent growth |
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Term
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Definition
| Bacterial contamination & growth |
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Term
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Definition
| Agent which destroys vegetative pathogens; usually on living tissue |
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Term
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Definition
| Lowering bacterial counts to safe public health levels |
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Term
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Definition
| • Microbiologists normally use log reduction to represent microbial kill. Most manufacturers of disinfectants speak in terms of percent kill. |
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Term
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Definition
| Time required to kill 90% (1 log) at a specific temperature. |
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Term
| Moist heat under pressure |
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Definition
| steam autoclave (121 C for 20 min) |
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Term
| Moist heat not under pressure |
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Definition
| pasteurization (63 C for 30 min or 72 C for 15 sec) |
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Term
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Definition
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Term
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Definition
| Chemiclave (132 C for 20 min using 15 psi of alcohol/formaldehyde vapor) |
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Term
| Action of Antimicrobial Agents |
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Definition
• 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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Term
| Alteration of Cell Walls and Membranes |
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Definition
• 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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Term
| Damage to Proteins and Nucleic Acids |
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Definition
• 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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Term
| Selection of Microbial Control Methods |
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Definition
• 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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Term
| Factors Affecting Disinfectant Action |
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Definition
• 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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Term
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Definition
• 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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Term
| Methods for Evaluating Disinfectants and Antiseptics |
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Definition
• Phenol Coefficient - Outdated
• Use-Dilution Test - AOAC
• Suspension Tests – Log reductions
• In-Use Tests – Samples taken before and after disinfection |
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Term
| The AOAC Use-Dilution Test: |
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Definition
| • Coat steel cylinders with dried bacteria: |
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Term
| Coat steel cylinders with dried bacteria: |
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Definition
– Staphylococcus aureus
– Pseudomonas aeruginosa
– Salmonella choleraesuis |
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Term
The AOAC Use-Dilution Test:
Physical Methods of Microbial Control |
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Definition
• Exposure to extremes of heat
• Exposure to extremes of cold
• Desiccation
• Filtration
• Osmotic pressure
• Radiation |
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Term
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and viruses within 10 minutes at sea level
• Temperature cannot exceed 100ºC 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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Term
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Definition
• Pressure applied to boiling water prevents steam from escaping
• Boiling temperature increases as pressure increases
• Autoclave conditions = 121ºC, 15 psi, 15 minutes |
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Term
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Definition
• 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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Term
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Definition
• 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 (106ºC for 2 hr or 171ºC for 1 hr)
• Incineration – ultimate means of sterilization |
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Term
| Refrigeration and Freezing |
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Definition
• 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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Term
| Desiccation and Lyophilization |
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Definition
• 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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Term
Membrane Filtration
Osmotic Pressure |
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Definition
• 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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Term
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Definition
• Shorter wavelength equals more energy and greater penetration
• Radiation described as ionizing or nonionizing according to effects on cellular chemicals |
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Term
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• 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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Term
| Chemical Methods of Microbial Control |
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Definition
• 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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Term
| Chemical Methods of Microbial Control |
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Definition
• Major Categories
– Phenols
– Alcohols
– Halogens
– Oxidizing agents
– Surfactants
– Heavy Metals
– Aldehydes
– Gaseous Agents
– Antimicrobics |
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Term
Some Representative Disinfectants:
Phenol and Phenolics |
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• “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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Term
Quaternary Ammonium Compounds (Quats)
Heavy Metals |
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Definition
• 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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Term
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Definition
• 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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Term
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Definition
• 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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Term
| Development of Resistant Microbes |
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Definition
• 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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Term
| Microbes in the Air (Aerobiology) |
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Definition
• 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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Term
| Eliminating Hands as Vehicles of Disease Transmission |
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Definition
• Gloves
• Antimicrobial hand treatments |
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Term
| Summary of Infection Control Best Agents for Specific Situations |
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Definition
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 |
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