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Physical and Chemical Control of Microorganisms
Lecture 10 Physical and Chemical Control of Microorganisms
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History First microbial control practices developed by Ignatz Semmelweis in 1800s Some techniques developed: Hand washing with chloride of lime Aseptic technique during surgery
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Microbial Control Sterilization: removal or destruction of all forms of microbial life Disinfection: aimed at destroying harmful microorganisms Antisepsis: disinfection directed at living tissue Degerming: mechanical removal of most of the microbes in an area Sanitation: intended to lower microbe counts to safe public health levels
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Rate of Microbial Death
When bacterial populations are heated or treated with antimicrobial agents they die at a constant rate Factors influencing the effectiveness of microbial treatments: # of microbes Environmental influences Time of exposure Microbial characteristics
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Physical Methods of Microbial Control
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Physical methods of microbial control
Heat Filtration Refrigeration Radiation Dessication Osmotic Pressure
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Heat Kills microbes by denaturing their enzymes Thermal Death Point:
Thermal Death Time: Three types: Moist heat, Pasteurization, Dry Heat
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Moist Heat Denatures proteins
Boiling: kills bacteria, viruses, fungi and their spores within 10 minutes Endospores and some viruses are not easily killed Autoclave: uses steam under pressure
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Pasteurization High temperature used for a short period of time to destroy pathogens without altering the flavor of the food
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Dry Heat Sterilization
Flaming- heat wire to red glow Hot-air sterilization- place items in oven- temperature 170oC for 2 hours ensures sterilization
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Filtration Passage of a liquid or gas through a filter with pores small enough to retain microbes Microbes can be removed from air by high-efficiency particulate air filters Membrane filters are commonly used to filter out bacteria, viruses, even large proteins from liquids
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Refrigeration Different types of bacteria have optimum growth temperatures Those that are infectious to humans generally grow best at human body temperature By putting something in fridge you are slowing the growth of these organisms
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Radiation Effects of radiation depend on wavelength, intensity, and duration Ionizing Radiation- ionizes water, forms highly reactive hydroxyl radicals Non-ionizing Radiation- UV light damages DNA Microwaves- do not have much effect on microorganisms
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Dessication Dessication: absence of water
Microorganisms cannot grow or reproduce but can remain viable for years Viruses and endospores can generally resist desiccation
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Osmotic Pressure Microorganisms at high concentrations of salt and sugars undergo plasmolysis Molds and yeasts are more capable than bacteria of growing in materials with low or high osmotic pressure
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Chemical Methods of Microbial Control
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Antiseptics and Disinfectants
The agent should be able to: Kill or slow growth of microbe Non-toxic to humans and animals Soluble in water, good shelf life Useful in diluted form Able to perform job in short time
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Antiseptics and Disinfectants
Several parameters should be considered: Temperature pH Stability
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Halogens Oxidize proteins Examples: Chlorine and Iodine
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Phenol and Phenolics Denature Proteins
Phenol- strong odor; caustic to skin Phenolics used more often
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Heavy Metals Interfere with microbial metabolism
Believed to bind protein molecules, making them unusable
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Alcohols Denature proteins and disrupt membranes
Preferred alcohol- ethyl alcohol
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Soaps and Detergents Act as surface active agents Not bacteriocidal
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Hydrogen Peroxide Breaks down into toxic form of oxygen
Not good on open wounds
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Antiseptics in your pantry
Cinnamon Garlic Honey Wasabi
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Figure 7.11
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