Heat denatures enzymes thermal death point tdp lowest

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Heat denatures enzymes Thermal death point (TDP): lowest temperature at which all cells in a liquid culture are killed in 10 min Thermal death time (TDT): minimal time for all bacteria in a liquid culture to be killed at a particular temperature Decimal reduction time (DRT) Minutes to kill 90% of a specific population of bacteria at a given temperature Pasteurization reduces spoilage organisms and pathogens High-temperature short-time (HTST): 72 ° C for 15 sec Thermoduric organisms survive
Moist Heat Sterilization Moist heat coagulates/denatures proteins Boiling Free-flowing steam Autoclave: steam under pressure 121°-C at 15 psi for 15 min Kills all organisms and endospores Steam must contact the item's surface Large containers require longer sterilization times Test strips are used to indicate sterility Dry Heat Sterilization Kills by oxidation Flaming Incineration Hot-air sterilization Filtration Passage of substance through a screenlike material Used for heat-sensitive materials High-efficiency particulate air (HEPA) filters remove microbes > 0.3 μ m in diameter Membrane filters remove microbes > 0.22 μ m Pore sizes of as small as 0.01 μ m are available, which can filter out viruses and large proteins Radiation Ionizing radiation (X-rays, gamma rays, electron beams) Ionizes water to create reactive hydroxyl radicals Damages DNA by causing lethal mutations Nonionizing radiation (ultraviolet, 260 nm) Damages DNA by creating thymine dimers Microwaves kill by heat; not especially antimicrobial Physical Methods Low temperature has a bacteriostatic effect Refrigeration Deep-freezing Lyophilization (freeze drying) High pressure denatures proteins Desiccation: absence of water prevents metabolism Osmotic pressure uses high concentrations of salts and sugars to create hypertonic environment; causes plasmolysis
Chemical Phenol and Phenolics: Injure lipids of plasma membranes, causing leakage Bisphenols: Contain two phenol groups connected by a bridge. Hexachlorophene and triclosan. Disrupt plasma membranes Biguanides: Chlorhexidine. Used in surgical hand scrubs. Disrupt plasma membranes Essential Oils Mixtures of hydrocarbons extracted from plants Peppermint oil, pine oil, orange oil Used for centuries in traditional medicine and for preserving food Microbial action primarily due to phenolics and terpenes Stronger activity against gram-positive bacteria; effectiveness against viruses not studied to date Halogens Iodine Tincture: solution in aqueous alcohol Iodophor: combined with organic molecules Impairs protein synthesis and alters membranes Chlorine Oxidizing agents; shut down cellular enzyme systems Bleach: hypochlorous acid (HOCl) Chloramine: chlorine + ammonia Alcohols Denatures proteins and dissolves lipids No effect on endospores and nonenveloped viruses Ethanol and isopropanol Require water Heavy Metals and their Compounds Oligodynamic action—very small amounts exert antimicrobial activity Denature proteins

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