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Process by which all life forms (including bacterial endospores & viruses) are either destroyed or removed from an object or habitant. |
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-Agent/method used to sterilize. - -Chemicals, heat, radiation |
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Killing, inhibition, or removal of microorganisms that may cause disease. èMajor goal is to kill potential pathogens èMight not kill Endospores! |
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Agents or chemicals used to carry out disinfection. èNormally used on inanimate objects èEthanol, cationic detergents |
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microbes are reduced to levels “considered safe by public health standards” (= cleaned and partially disinfected.) |
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Reduction of total microbial population on living tissue prevention of infection. |
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Chemical agents applied to tissue to prevent infection by killing or inhibiting pathogen growth |
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- Latin “cida” = kill - - Method or agent that kills microbes, not necessarily endospores - - i.e. bactericide, fungicide, algicide, viricide - |
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- Static (Greek “statikos”) = halt or stop - Method or agent that stops bacterial growth - Must be continually present |
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The Pattern of Microbial Death |
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•microorganisms are not killed instantly •(Like growth) population death usually occurs exponentially (population will be reduced by the same fraction at constant intervals). •microorganisms are considered to be dead when they are unable to reproduce in conditions that normally support their reproduction |
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D value (decimal reduction time) |
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Definition
Time required to kill 90% of microorganism at a specific temperature. |
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Factors affecting Antimicrobials |
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Definition
Œ Population size Population composition Ž Duration of exposure Concentration or intensity of agent Temperature ‘ Local environment |
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Larger populations take longer to kill. An equal fraction of population killed each time interval |
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Microbes in Population Toughest to kill -- bacterial endospores Other “tough bugs” Mycobacterium tuberculosis (causes tuberculosis) is very resistant to many antimicrobial agents State of Microbes “vegetative” growing cells easier to kill |
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Longer exposure = more cell death |
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Concentration and Temperature of Agent |
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Increased concentration and/or temp enhances activity of antimicrobial agent |
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pH, viscosity, organic matter - Organic matter inhibits chemical agents |
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Actions of Microbial Growth Control Agents |
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Definition
Effect on membrane Agents cause leakage of cellular contents Damage to proteins and/or nucleic acids Proteins - can be denatured or inhibited Nucleic acids - can be damaged or broken |
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Methods of Microbial Growth Control |
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Definition
- Physical control methods Heat, Low temperature, Radiation, Filtration - Chemical control methods Alcohols, Aldehydes, Detergents, etc. Heat |
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Methods of Microbial Growth Control Heat |
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Definition
- Advantages: Widely-used methods Inexpensive and easy to apply - Disadvantages: May not sterilize (Ex: Endospores) Some items are damaged by heating |
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- Thermal death time (TDT) |
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Definition
minimum time needed to kill organisms in a suspension at a specific temp. under defined conditions |
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- Decimal Reduction Time (D): |
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Definition
Time required to kill 90% of microbes in sample at a specific temp Ex: D60 = 0.4 min At 60o C, 0.4 min kills 90% of cells Note: D value is temperature-dependent |
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increase in temperature required to reduce D to 1/10 (D= Time required to kill 90% of microbes in sample at a specific temp) |
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Methods of Microbial Growth Control - Dry Heat - |
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Definition
- Hot oven 170oC for 2 hrs will sterilize Used for glassware, glass pipettes - Direct flaming Bunsen burner - inoculating loops Incineration - trash, contaminated materials |
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Methods of Microbial Growth Control - Moist Heat - |
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Definition
Boiling 10 min kills vegetative cells Useful for sanitization Will not kill bacterial spores Autoclave: uses saturated steam under pressure to reach temps above boiling: 121oC at 15 lbs/in2 will sterilize bacterial endospores killed in 10-12 min. Used to sterilize culture media, surgical instruments (Any items that can withstand heat) • |
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Definition
-In honor of its developer Louis Pasteur. - -Discovered that a brief heating at ~60oC would destroy microorganism in wine and preserve it for long periods. Controlled heating (well below boiling) to kill pathogens & slows spoilage of beverages by reducing the level of non-pathogenic spoilage microorganisms. - |
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Methods of Microbial Growth Control - Filtration - |
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Definition
Filter size excludes microbes Usually <0.2 mm Used for heat-sensitive agents Examples: antibiotics, vitamins, amino acids Filtering air •surgical masks •cotton plugs on culture vessels •high-efficiency particulate air (HEPA) filters –used in laminar flow biological safety cabinets |
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Methods of Microbial Growth Control - Low temperature - |
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Refrigeration (4oC) or Freezing (-20oC): Freezing stops reproduction due to lack of liquid water. Some bacteria may be killed by ice crystal disruption of cell membranes Is bacteriostatic (not -cidal) |
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Methods of Microbial Growth Control - Radiation - Ionizing radiation |
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Definition
Ionizing radiation: X-rays, Gamma rays: deep penetration Kills bacterial spores, etc. A “cold sterilization” method Used to sterilize lab and medical supplies Generates e-, OH●, and H● Highly reactive, disrupt DNA & Protein! |
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Methods of Microbial Growth Control - Radiation - |
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Definition
Non-ionizing radiation: UV light, Wavelength - 260 nm “Germicidal lamps” (Damages DNA & kills germs) Useful only for surface sterilization Poor penetration of glass, water, etc. |
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| Microbes resistant to radiation |
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Definition
Clostridium botulinum Endospores: D10 = 39600 Gy Deinococcus radiodurans 500-times more resistant than human àmultiple copies of its genome and rapid DNA repair mechanisms à "Conan the Bacterium" à |
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Other Physical Methods of Microbial Growth Control |
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Definition
•Desiccation –Drying - bacteriostatic –Ex: Freeze-dried foods – • Osmotic Pressure –High concentrations of sugars or salts –Ex: Food preservation - jams, salted meats • |
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Chemical Methods of Microbial Growth Control Ideal chemical agent |
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Definition
Ideal chemical agent: •Active against wide range of microbes •Non-corrosive and nontoxic •Soluble in water, long shelf-life •Non-staining, pleasant odor •Cost-effective |
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Definition
Phenol & Phenol Derivatives: Denature Protein & disrupt cell membranes Alcohols (Ethanol, Isopropanol) Denatures proteins & dissolve membrane lipids Problem: Does not kill spores Halogens (Iodine) CAntiseptic Oxidizes cell constituents & iodinates proteins Heavy Metals (Copper) C Algicide in water Problem: Toxic! Detergents (Quaternary ammonium compounds) CCleaning and sanitization in hospitals & labs Problem: Doesn’t kill some G- bacteria Aldehydes (Formaldehyde) C Sterilize surgical instruments Combine with and inactivate nucleic acid and proteins Problem: Allergical Reaction Sterilizing Gases (Ethylene oxide) CSterilization of heat-sensitive medical equipment Kills bacteria, mold & fungi |
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Evaluation of Chemical Control Methods |
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Definition
•Use-dilution tests: rate at which selected bacteria are destroyed 95% –Standard test organisms: –Staphylococcus, Salmonella, Pseudomonas – • Phenol Coefficient –Dilutions of test agent compared to dilution of phenol –Ratio- 1 / test dilution : 1 / phenol dilution •Phenol Coefficient Example: –Max activity of Agent A: 1/450 –Max activity of Phenol: 1/90 • •PC = 450 / 90 = 5 •PC > 1 Agent is more effective than phenol – |
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