physical and chemical control of microbesfaculty.rcc.edu/herrick/microbio 1/unit iii... · 5....
TRANSCRIPT
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Physical and Chemical Control of Microbes
Physical and chemical methods to destroy or reduce microbes in a given area
Control of microbes
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Relevant Terms
• Sterilization – a process that destroys all viable microbes, including viruses & endospores
• Disinfection – a process to destroy vegetative pathogens, not endospores
• Sanitization – any cleansing technique that mechanically removes microbes
• Degermation – reduces the number of microbes
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Factors That Influence The Action of Antimicrobial Agents:
1. Number of microbes
2. Nature of microbes in the population
3. Temperature & pH of environment
4. Concentration or dosage of agent
5. Mode of action of the agent
6. Presence of organic matter, biofilms
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Cellular Targets for Microbial Control
1. Cell wall 2. Cell membrane 3. DNA and RNA synthesis 4. Proteins
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Methods of Physical Control
1. Heat 2. Cold temperatures 3. Desiccation 4. Radiation 5. Filtration
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1. Heat Moist heat – use of hot water and/or steam
• Mode of action – denaturation of proteins, destruction of membranes & DNA • Sterilization • autoclave 15 psi above atmospheric pressure/121oC/10-40min • Intermittent sterilization – unpressurized steam at 100oC 30-60 min for 3 days • Disinfection • Boiling at 100oC for 30 minutes to destroy non-spore-forming pathogens • Pasteurization <100oC for seconds; kills Salmonella, Listeria & decreases overall
microbe count
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Autoclaves
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Pasteurization
• Used when taste of product would be damaged by longer heating: lowers numbers of pathogens (63°C for 30 minutes)
• High-temperature short-term (HTST) pasteurization (72°C for 15 seconds)
• UHT: sterilization (140°C for 3 seconds)
1. Heat
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Dry heat using higher temperatures than moist heat, can also sterilize – Dry ovens – Usually used for metals and glassware – Incineration – 600-1200oC combusts & dehydrates cells (flaming your loop!) – Only suitable means to sterilize oils and powders
1. Heat
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2. Cold Temperatures
• Microbiostatic – slows the growth of microbes
• Refrigeration 0 - 15 °C & freezing <0°C
• Used to preserve food, media and cultures
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3. Desiccation/Drying
• Gradual removal of water from cells, leads to metabolic inhibition
• Not effective microbial control – many cells retain ability to grow when water is reintroduced
Lyophilization (Freeze-drying) – is the drying of material from the frozen state
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4. Radiation
1. Ionizing radiation – deep penetrating power, breaks DNA, – gamma rays, X-rays, cathode rays – used to sterilize medical supplies & food products
2. Nonionizing radiation – little penetrating power to sterilize air, water & solid surfaces
– uv light creates thymine dimers, which interfere with replication
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Ultraviolet Radiation and Water Treatment
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5. Filtration
• Physical removal of microbes by passing a gas or liquid through filter
• Used to sterilize heat sensitive liquids & air in hospital isolation units & industrial clean rooms
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Chemical Control of Microbial Growth
1. Halogens 2. Phenolics 3. Chlorhexidine 4. Alcohols 5. Hydrogen peroxide 6. Detergents & soaps 7. Heavy metals 8. Aldehydes (Alkylating Agents) 9. Gasses and Aerosols
Sporocide: An agent that kills bacterial endospores or fungal spores
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Structural Formulas of Some Important Disinfectants
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1. Halogens
• Chlorine – Cl2, hypochlorites (chlorine bleach), chloramines – Denaturation of proteins by disrupting disulfide bonds – Can be sporicidal
• Iodine - I2, iodophors (betadine) – Denature proteins – Can be sporicidal – Milder medical & dental degerming agents, disinfectants,
ointments
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2. Phenolics
• Disrupt cell membranes & precipitating proteins; bactericidal, fungicidal, virucidal, not sporicidal – Lysol – triclosan- antibacterial additive to soaps
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3. Chlorhexidine
• Halogens combined with phenols (halogenated phenols)
• Hibiclens, Hibitane
• A surfactant & protein denaturant with broad microbicidal properties
• Not sporicidal
• Used as skin degerming agents for preoperative scrubs, skin cleaning & burns
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Disinfectants & Antiseptics
• Kill/inhibit growth of microbes on surfaces • Phenols and phenolics: damage lipid membranes
– Active in presence of organic matter – Stable – Persist for long periods after application – Broad spectrum of activity
Lysol Triclosan (antibacterial additive to soaps)
Phenolics & Chlorhexidines - Summary
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• Chlorhexidines – Low toxicity – Used on skin and mucous membranes
Degerming agent, pre-op scrub, burns…
Hibiclens, Hibitane
Phenolics & Chlorhexidines - Summary
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4. Alcohols
• Ethyl, isopropyl in solutions of 50-90%
• Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi
• Not sporicidal
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5. Hydrogen Peroxide
• Weak (3%) to strong (25%)
• Produce highly reactive hydroxyl-free radicals that damage protein & DNA while also decomposing to O2 gas – toxic to anaerobes
• Strong solutions are sporicidal
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6. Detergents & Soaps
• Quaternary ammonia compounds (quats) act as surfactants that alter membrane permeability of some bacteria & fungi – Not sporicidal – Can support the growth of some Pseudomonas bacteria – Usually mixed with other agents (usually alcohol) as a result
of this problem – Foaming mouthwashes usually contain a quat.
• Soaps- mechanically remove soil and grease containing microbes
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Quaternary Ammonium Compounds
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7. Heavy Metals
• Solutions of silver & mercury kill vegetative cells in low concentrations by inactivating proteins – Examples: silver nitrate, mercurochrome, thimerosal
• Not sporicidal
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8. Aldehydes (Alkaylating Agents)
• Glutaraldehyde & formaldehyde kill by alkylating protein & DNA
• Glutaraldehyde in 2% solution (Cidex) used as sterilant for heat sensitive instruments
• Formaldehyde - disinfectant, preservative, toxicity limits use
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9. Gases & Aerosols
• Ethylene oxide, propylene oxide, betapropiolactone & chlorine dioxide
• Strong alkylating agents, sporicidal
• Very toxic! Ethylene oxide vapors are toxic to skin, eyes and mucus membranes. May be carcinogenic.
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Chemical Food Preservatives
• Used in foods to inhibit microbial growth – Sulfur dioxide – Sodium benzoate – Sorbic acid – Calcium propionate – Sodium nitrate and sodium nitrite
FYI - You don’t need to memorize these…