Lecture 10 Physical and Chemical Control of Microorganisms.
-
Upload
jade-stanley -
Category
Documents
-
view
229 -
download
2
Transcript of Lecture 10 Physical and Chemical Control of Microorganisms.
![Page 1: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/1.jpg)
Lecture 10
Physical and Chemical Control of Microorganisms
![Page 2: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/2.jpg)
History
• First microbial control practices developed by Ignatz Semmelweis in 1800s
• Some techniques developed:– Hand washing with chloride of lime– Aseptic technique during surgery
![Page 3: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/3.jpg)
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
![Page 4: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/4.jpg)
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
![Page 5: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/5.jpg)
![Page 6: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/6.jpg)
Physical Methods of Microbial Control
![Page 7: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/7.jpg)
Physical methods of microbial control
• Heat• Filtration• Refrigeration• Radiation• Dessication• Osmotic Pressure
![Page 8: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/8.jpg)
Heat
• Kills microbes by denaturing their enzymes• Thermal Death Point:
• Thermal Death Time:
• Three types:– Moist heat, Pasteurization, Dry Heat
![Page 9: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/9.jpg)
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
![Page 10: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/10.jpg)
![Page 11: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/11.jpg)
Pasteurization
• High temperature used for a short period of time to destroy pathogens without altering the flavor of the food
![Page 12: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/12.jpg)
Dry Heat Sterilization
• Flaming- heat wire to red glow• Hot-air sterilization- place items in oven-
temperature 170oC for 2 hours ensures sterilization
![Page 13: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/13.jpg)
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
![Page 14: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/14.jpg)
![Page 15: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/15.jpg)
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
![Page 16: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/16.jpg)
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
![Page 17: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/17.jpg)
Dessication
• Dessication: absence of water• Microorganisms cannot grow or reproduce
but can remain viable for years• Viruses and endospores can generally resist
desiccation
![Page 18: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/18.jpg)
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
![Page 19: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/19.jpg)
Chemical Methods of Microbial Control
![Page 20: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/20.jpg)
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
![Page 21: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/21.jpg)
Antiseptics and Disinfectants
• Several parameters should be considered:– Temperature–pH– Stability
![Page 22: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/22.jpg)
Halogens
• Oxidize proteins• Examples: Chlorine and Iodine
![Page 23: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/23.jpg)
Phenol and Phenolics
• Denature Proteins• Phenol- strong odor; caustic to skin• Phenolics used more often
![Page 24: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/24.jpg)
Heavy Metals
• Interfere with microbial metabolism• Believed to bind protein molecules, making
them unusable
![Page 25: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/25.jpg)
Alcohols
• Denature proteins and disrupt membranes• Preferred alcohol- ethyl alcohol
![Page 26: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/26.jpg)
Soaps and Detergents
• Act as surface active agents• Not bacteriocidal
![Page 27: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/27.jpg)
Hydrogen Peroxide
• Breaks down into toxic form of oxygen• Not good on open wounds
![Page 28: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/28.jpg)
Antiseptics in your pantry
• Cinnamon• Garlic• Honey• Wasabi
![Page 29: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/29.jpg)
![Page 30: Lecture 10 Physical and Chemical Control of Microorganisms.](https://reader036.fdocuments.in/reader036/viewer/2022062408/56649e185503460f94b04982/html5/thumbnails/30.jpg)
Figure 7.11