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Microbial Control Text Summary

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Humber College
BIOL 326

1/01 MICROBIAL CONTROL Answer questions on work sheet. Terminology A. Sterilization - kills all microbes present B. Disinfection - reduces the number (control) of pathogens C. Sanitization - reduction in number of microbes present to safe (accepted) levels D. Two types of methods of microbial control 1. Physical methods 2. Chemical methods Physical methods A. Heat 1. Most common method, effective, least expensive 2. Denatures (coagulates) cell proteins (enzymes) 3. Two forms: moist heat, dry heat B. Moist heat methods 1. Boiling a. 98 -100°C/10 min. b. Inactivates most vegetative cells, not heat-resistant forms (endospores, some viruses & bacterial toxins) c. Drinking water, canning jars, etc. 2. Autoclave - steam under pressure, ↑ temperature steam a. 15# pressure/121°C/15 - 20 min. b. Destroys all forms - sterilization c. In addition to coagulating proteins, causes hydrolysis d. Media, surgical instruments, etc. 3. Pasteurization a. Heat material, holding at specific temperature for specific length of time, cool rapidly b. Low Temperature Long Term (Holding) method: 62°C for 30 min. c. High Temperature Short Term method: 72°C for 15 sec. d. Ultrahigh Temperature method: 140°C/15 sec.; 149°C/0.5 sec. e. Inactivates pathogens, reduces total microbial population f. Does not sterilize f. Dairy products, wine, beer, etc. C. Dry heat methods 1. Hot air ovens a. 160 - 170°C/2 - 3 hrs. b. Causes oxidation of microbes, sterilizes c. Used when moisture undesirable - glassware, metals, powders or petroleum-based products (oils). 1 1/01 2. Incineration a. Burning - oxidation b. Must be complete c. Regulations to control release of ashes, odor d. Used to destroy disposable items, soiled dressings, tissue specimens. e. Flaming loop, tubes - form of incineration D. Filtration 1. Solids physically separated from liquids by passage through filters with extremely small pores (porcelain, ground glass, diatomaceous earth, asbestos, sand, membrane filters) 2. Liquids mechanically forced or pulled through (using a vacuum) filters which trap microbes 3. Does not sterilize unless pore size small enough to trap all organisms 4. Uses: materials (media, medications) that can't be heated, beer and wine, swimming pools and spas, sewage, air, testing water or air for organisms or allergens E. Radiation 1. Two types commonly used a. Ionizing rays (X-rays, gamma rays) b. Nonionizing rays (UV light) 2. Cause lethal changes in DNA, denatures proteins (produces hyperactive ions and free radicals) 3. UV light a. Of limited use, cannot penetrate materials (cloth, glass, paper, etc.) b. Used to reduce number organisms in air, on clean surfaces 4. Gamma rays, X-rays a. More effective, can penetrate materials b. Used to sterilize plastics, medications, foods (retards spoilage) F. Methods used for preservation 1. Increased osmotic pressure a. High concentrations of salt, sugar b. Dehydrates cells, more effective against bacteria than fungi c. Use: food preservation 2. Desiccation a. Drying, removal of water b. Retards, but does not always kill c. More effective against bacteria than fungi d. Use: food preservation 3. Acid, alkaline pH a. Inactivates enzymes, inhibits growth b. Does not always destroy microbes c. Uses: acid pH (benzoic, sorbic, propionic acids) - food preservation 2 1/01 4. Decreased temperatures a. Refrigerator 1) 5 - 10°C 2) Retards growth, does not prevent growth b. Freezer 1) Below O°C (-10°C) 2) Prevents growth, does not kill all organisms 5. Lyophilization - freeze-drying a. Materials rapidly frozen at temperatures well below O°C. (ice crystals formed are very small minimizing damage to cells) b. Exposure to vacuum while in frozen state to remove moisture c. Very effective (expensive) method of preservation d. Uses: biological specimens (cultures), medications, foods Chemical Methods A. Two groups chemical agents 1. Disinfectants - used on inanimate objects 2. Antiseptics - used on viable tissues B. Terms used to describe effect of chemical agents end in the suffix: 1. "cide" - killing effect (bactericide) 2. "static" - inhibits growth (bacteriostatic) C. Action of chemical agents (disinfectants, antiseptics) 1. Injury to cytoplasmic membrane or viral envelopes a. Solvents - dissolve lipids b. Affect pore size c. Causes leakage of cell contents, prevents absorption of nutrients, remove viral envelope. 2. React on cell proteins (enzymes, cell components). a. Coagulation - inactivates proteins b. Chemical reactions with proteins (hydrolysis, oxidation, attachment of atoms or chemical groups) c. Causes changes in structure. 3. Affect nucleic acids a. Inhibit replication b. Change in structure D. Factors that determine the effectiveness of chemical agents (disinfectants, antiseptics) 1. Chemical structure (form) of agent - may be more effective in one form than another. 2. Water soluble - absorbed by microbes 3. Stable in solution - not affected by pH, heat, light, etc. 4. Low surface tension - increases ability to spread and adhere to surfaces 5. Temperature - 10° increase doubles activity of chemical agent (increases absorption, cell metabolism). 6. Concentration - influences absorption and action of chemical agent. 7. Time - required to affect microbes varies 8. Presence of organic material - retards penetration of chemical agent (object must be cleaned thoroughly before treated with chemical agent). 3 1/01 E. READ: Families of chemicals used as germicides and their action on microbes. F. Gas sterilization - Ethylene Oxide
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