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54 Cards in this Set
- Front
- Back
Physical, chemical, and mechanical methods... |
To destroy or reduce undesirable microbes in a given area (decontamination) |
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Primary targets are microorganisms capable of causing infection or spoilage, such as... |
Vegetative bacterial cells and endospores Protozoan trophozoites and cysts Fungal hyphae and spores, yeast Worms Viruses and prions |
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Sterilization |
A process that destroys all viable microbes, including viruses and endospores |
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Disinfection |
A process to destroy vegetative pathogens, not endospores; inanimate objects |
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Antiseptic |
Chemicals applied directly to exposed body surfaces |
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Sanitation |
Any cleansing technique that mechanically removes microbes |
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Highest resistance microbes |
Prions, bacterial endospores |
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Moderate resistance |
Psudomonas sp. Mycobacterium tuberculosis S. aureus Protozoan cysts |
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Least resistance |
Most bacterial vegetative cells Fungal spores and hyphae, yeast Enveloped viruses Protozoa trophozoites |
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Microbial death |
Permanent loss of reproductive capability, even under optimum growth conditions |
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Factors that affect death rate |
Number of microbes Composition of microbes in the population Temp and pHof environment Concentration or dosage of agent Mode of action of the agent Presence of solvents, organic matter, or inhibitors |
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Practical concerns in microbial control |
Does the application require sterilization? Is the item to be reused? Can the item withstand heat, pressure, radiation, or chemical? Is method suitable? Will agent penetrate to the necessary extent? Is the method cost- and labor-efficient and is it safe? |
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Cellular targets of physical and chemical agents |
Cell wall and cell membrane |
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Cell wall |
Becomes fragile and cell lyses; some antimicrobial drugs, detergents, and alcohol |
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Cell membrane |
Loses integrity; detergents or surfactants |
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Cellular targets of physical and chemical agents |
Protein and NA synthesis: prevention of replication, transcription, translation, peptide bond formation, protein synthesis, chloramphenicol, UV radiation, formaldehyde Proteins: disrupt or denature proteins, alcohols, phenols, acids, heat |
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Methods of physical control |
Heat-moist and dry Cold temperatures Desiccation Radiation Filtration |
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Bacterial endospores are most/least resistant and usually require temperatures above/below boiling |
Most and above |
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Thermal death time |
Shortest length of time required to kill all test microbes at a specified temp |
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Thermal death point |
Lowest temperature required to kill all microbes in a sample in 10 minutes |
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Steam under pressure |
Sterilization |
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Autoclave |
15 psi/121C/10-40 minutes Steam must reach surface of item being sterilized Item must not be heat or moisture sensitive Mode of action-denaturation of proteins, destruction of membranes, and DNA |
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Tyndallization |
Intermittent sterilization for substances that cannot withstand autoclaving Items exposed to free-flowing steam for 30-60 minutes, incubated for 23-24 hours and then subjected to steam again Repeat cycle for 3 days Used for some canned foods and lab media |
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Boiling water |
Boiling at 100C for 30 minutes to destroy non-spore forming pathogens Disinfection |
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Pasteurization |
Heat is applied to oil potential agents of infection and spoilage w/o destroying the food flavor or value 63C-66C for 30 minutes 71.6C for 15 seconds Not sterilization-kills non-spore-forming pathogens and lowers overall microbe count; does not kill endospores or many nonpathogenic microbes |
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Dry heat |
Using higher temps than moist heat |
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Incineration |
Flame or electric heating coil Ignites and reduces microbes and other substaces |
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Dry ovens |
150-180C Coagulate proteins |
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Microbiostatic |
Slows the growth of microbes Refrigeration 0-15C and freezing 0C Used to preserve food, media, and cultures |
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Desiccation |
Gradual removal of water from cells, leads to metabolic inhibition Not effective microbial control-many cells retain ability to grow when water is reintroduced |
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Lyophilization |
Freeze drying; preservation |
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Ionizing radiation |
Deep penetrating power that has sufficient energy to cause electrons to leave their orbit, breaks DNA Gamma X-rays, cathod rays used to sterilize medical supplies and food products |
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Nonionizing radiation |
Little penetrating power so it must be directly exposed UV light creates pyrimidine dimers, which interfere with replication |
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Filtration |
Physical removal of microbes by passing a gas or liquid through filter Used to sterilize heat sensitive liquids and air in hospital isolation units and industrial clean rooms |
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Chemical agents in microbial control |
Disinfectants, antiseptics, sterilants, and preservatives |
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Some desirable qualities of chemicals |
Rapid action in low concentration Solubility in water or alcohol, stable Broad spectrum, low toxicity Penetrating Noncorrosive and nonstaining Affordable and readily available |
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High-level germicides |
Kill endospores; may be sterilants Devices that are not heat sterilizable and intended to be used in sterile environments (body tissues) |
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Intermediate-level germicides |
Kill fungal spores (not endospores), tubercle bacillus, and viruses Used to disinfect devices that will come in contact with mucous membranes but are not invasive |
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Low-level germicides |
Eliminate only vegetative bacteria, vegetative fungal cells, and some viruses Clean surfaces that touch skin but not mucous membranes |
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Factors that affect germicidal activity of chemicals |
Nature of the material being treated Degree of contamination Time of exposure Strength and chemical action of the germicide |
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Germicidal categories |
Halogens, phenolics, chlorhexidine, alcohols, hydrogen peroxide, aldehydes, gases, detergents and soaps, heavy metals, dyes, acids and alkalis |
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Halogens |
Chlorine-Cl2, hypochlorites, and chloramines Denature proteins by disrupting disulfide bonds Intermediate level Unstable in sunlight, inactivated by organic matter Water, sewage, wastewater, inanimate objects |
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Iodine |
I2, iodophore (betadine) Interferes with disulfide bonds of proteins Intermediate level Milder medical and dental degerming agents, disinfectants, ointments |
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Phenolics |
Disrupt cell walls and membranes and precipitate proteins Low to intermediate level Bactericidal, fungicidal, virucidal, not sporicidal Example: Lysol Ticlosan-antibacterial additive to soaps |
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Chlorhexidine |
A surfactant and protein denaturant with broad microbicidal properties Low to intermediate level Hibiclens, hibitane Used as skin degerming agents for preoperative scrubs, skin cleaning, and burns |
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Alcohols |
Ethyl, isopropyl in solutions of 50-95% Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi Intermediate level |
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Hydrogen Peroxide |
Produce highly reactive hydroxyl-free radicals that damage protein and DNA while also decomposing to O2 gas-toxic to anaerobes Antiseptic at low concentrations; strong solutions are sporicidal |
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Aldehydes |
Kill by alkylating protein and DNA Glutaraldehyde in 2% sol used as sterilant for heat sensitive instruments (high level) Formaldehyde: disinfectant, preservative, toxicity limits use Formalin-37% aqueous solution Intermediate to high level |
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Gases and Aerosols |
Ethylene oxide, propylene oxide Strong alkylating agents High level Sterilize and disinfect plastics and prepackaged devices, foods |
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Detergents and Soaps |
Quaternary ammonia compounds act as surfactants that alter membrane permeability of some bacteria and fungi Very low level |
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Soaps |
Mechanically remove soil and grease containing microbes |
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Heavy metals |
Solutions of silver and mercury kill vegetative cells in low concentrations by inactivating proteins Oligodynamic action Low level Merthiolate, silver nitrate, silver |
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Dyes as Antimicrobial Agents |
Aniline dyes are very active against gram-positive species of bacteria and various fungi Sometimes used for antisepsis and wound treatment Low level, narrow spectrum of activity |
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Acids and Alkalis |
Low level of activity: Organic acids prevent spore germination and bacterial and fungal growth Acetic acid inhibits bacterial growth Propionic acid retards molds Lactic acid prevents anaerobic bacterial growth Benzoic and sorbic acid inhibit yeast |