Microbio Ch 11 – Flashcards
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| Controlling Microorganisms |
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| Physical, chemical, and mechanical methods to destroy or reduce undesirable microbes in a given area (decontamination) ; Primary targets are microorganisms capable of causing infection or spoilage: a) Vegetative bacterial cells and endospores, b) Fungal hyphae and spores, yeast, C) Protozoan trophozoites and cysts, D) Worms, E) VirusesF) Prions |
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| Relative Resistance of Microbes |
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| picture |
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| Highest resistance |
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| Prions, bacterial endospores |
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| Moderate resistance |
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| Pseudomonas sp., Mycobacterium tuberculosis, Staphylococcus aureus, Protozoan cysts |
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| Least resistance |
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| Most bacterial vegetative cells, Fungal spores and hyphae, yeast, Enveloped viruses, Protozoan trophozoites |
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| Sterilization |
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| a process that destroys all viable microbes, including viruses and endospores ex) autoclaving, ionizing radiation (correctly applied) |
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| Disinfection |
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| a process to destroy vegetative pathogens, not endospores; inanimate objects ex) 5% bleach, boiling water |
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| antiseptic |
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| disinfectants applied directly to exposed body surfaces ex) iodophors, antibacterial soap, chlothexidine |
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| Sanitization |
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| any cleansing technique that mechanically removes microbes ex) dishwashing, laundering clothes |
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| Degermation |
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| reduces the number of microbes through mechanical means ex) surgical handscrub |
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| Microbial Death |
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| Microbes are “dead” when they no longer replicate.; Hard to detect, microbes often reveal no conspicuous vital signs to begin with ; Permanent loss of reproductive capability, even under optimum growth conditions |
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| Factors That Affect Death Rate |
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| number of microbes; nature of microbes in the population; temperature and pH of 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, Selection of method of control depends on: |
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| Does the application require sterilization? ; Is the item to be reused? ; Can the item withstand heat, pressure, radiation, or chemicals? ; Is the method suitable?; Will the agent penetrate to the necessary extent? ; Is the method cost- and labor-efficient and is it safe? |
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| Antimicrobial Agents’ Modes of Action |
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| Cellular targets of physical & chemical agents: 1.The cell wall (cell wall becomes fragile and cell lyses; example: some antimicrobial drugs, detergents, alcohol) ; 2.The cell membrane (loses integrity; Examples: detergent or surfactants); 3. Protein and nucleic acid synthesis---prevention of a) replication, transcription or translation, ,b) peptide bond formation, c) protein synthesis (examples: chloramphenicol, ultraviolet radiation, formaldehyde) 4)Proteins --disrupt or denature proteins( examples: alcohols, phenols, acids, heatProtein Denaturation) |
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| Moist heat |
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| lower temperatures and shorter exposure time; coagulation and denaturation of proteins.. time to sterilize 15 min (121C) |
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| Dry heat |
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| moderate to high temperatures; dehydration, alters protein structure; incineration.. time to sterilize 600 min (121C) |
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| Thermal Death Measurements |
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| Bacterial endospores most resistant – usually require temperatures above boiling |
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| Thermal death time (TDT |
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| – shortest length of time required to kill all test microbes at a specified temperature |
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| Thermal death point (TDP) |
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| lowest temperature required to kill all microbes in a sample in 10 minutes |
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| MOIST HEAT METHODS |
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| Steam under pressure – sterilization ; Autoclave – 15 psi/121oC/10-15 min ; Steam must reach surface of item being sterilized; Item must not be heat or moisture sensitive ; Mode of action – 1. denaturation of proteins 2. destroys membranes and DNA |
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| Boiling Water |
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| Boiling at 100oC for 30 minutes to destroy non-spore-forming pathogens |
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| Pasteurization |
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| heat is applied to kill potential agents of infection and spoilage without destroying the food flavor or value ; 63°C–66°C for 30 minutes (batch method) ; 71.6°C for 15 seconds (flash method) ; 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 |
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| using higher temperatures than moist heat; baking ; Incineration – flame or electric heating coil--Ignites and reduces microbes and other substances; Dry ovens – 150–180oC – coagulate proteins ; Using Heat for Sterilization and Disinfection |
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| Cold --Microbiostatic |
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| slows the growth of microbes; Refrigeration 0–15oC ; Freezing <0oC ; Used to preserve food, media, and cultures ; |
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| Desiccation |
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| Gradual removal of water from cells, leads to metabolic inhibition (not death) ; Not effective microbial control – many cells retain ability to grow when water is reintroduced ; Lyophilization – freeze drying; preservation |
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| Ionizing radiation |
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| deep penetrating power with sufficient energy to cause electrons to leave their orbit ; breaks DNA ; Gamma rays, X-rays, cathode rays ; Used to sterilize medical supplies and food products; Application of Ionizing Radiation: Preserving food with ionizing radiation |
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| Nonionizing radiation |
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| little penetrating power ;requires direct exposure ; UV light a pyrimidine dimers - interfere with replication ; Application of Nonionizing Radiation: Sterilizing air, water or surfaces |
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| Filtration |
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| Physical removal of microbes by passing a gas or liquid through a filter; 0.4mm – fungi, protozoa, algae, dirt, 0.2mm – bacteria ; Used to sterilize ---heat sensitive liquids----air in hospital isolation units and industrial clean rooms |
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| Chemical Agents in Microbial Control |
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| Disinfectants, antiseptics, sterilants, degermers, and preservatives; Some desirable qualities of chemicals: a) Rapid action in low concentration, b) Solubility in water or alcohol, stable c) Broad spectrum, low toxicity, d)Penetrating, e) Noncorrosive and nonstaining F)Affordable and readily available |
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| High-level germicides |
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| kill endospores; may be sterilants; Devices that are not heat sterilizable and intended to be used in sterile environments (body tissue |
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| Intermediate-level germidice |
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| – 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 germicide |
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| 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 |
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| Nature of the material being treated; Degree of contamination ; Time of exposure ; Strength and chemical action of the germicide ; Chemical Agents Used in Health Care ; |
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| Germicidal Categories |
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| 1.Halogens 2. Phenolics 3. Chlorhexidine 4.Alcohols 5.Hydrogen peroxide 6.Aldehydes 7.Gases 8. Detergents & soaps 9. Heavy metals 10. Dyes 11. Acids and Alkalis |
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| Halogens |
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| Chlorine – Cl2, hypochlorites (chlorine bleach), chloramines ; Denaturate proteins by disrupting disulfide bonds ; Intermediate level ; Unstable in sunlight, inactivated by organic matter ; Water, sewage, wastewater, inanimate objects ; Iodine - I2, iodophors (betadine); Interferes with disulfide bonds of proteins; Intermediate level ; Milder medical and dental degerming agents, disinfectants, ointments;. Phenolics --Disrupt cell walls and membranes and precipitate proteins ; --Low to intermediate level – bactericidal, fungicidal, virucidal, not sporicidal—Lysol; Triclosan – antibacterial additive to soaps |
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| Chlorhexidine |
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| 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 |
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| 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 |
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| 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 |
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| Kill by alkylating protein and DNA ---Glutaraldehyde in 2% solution (Cidex) 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 |
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| Ethylene oxide, propylene oxide ;Strong alkylating agents ; High level ; Sterilize and disinfect plastics and prepackaged devices, foods |
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| Detergents and Soaps |
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| Quaternary ammonia compounds (quats) act as surfactants that alter membrane permeability of some bacteria and fungi; Very low level ; soaps—mechanically remove soil and grease containing microbes |
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| Heavy Metals |
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| 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 |
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| Aniline dyes, like Crystal Violet, 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 |
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| 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 |
