TAKE HOME ESSAY Chapter 7 (could account fer one third of the Lecture Exam 21 3.
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TAKE HOME ESSAY Chapter 7 (could account fer one third of the Lecture Exam 21 3. Describe the Actions of Microbial Control Agents (page 178-179 of text book) stating amaged and SA y Sterial membrane robial Control Agents that actually kill or inhibit microbes and HOW bacterial proteins and nucleic acids are Six examples of Chemical agents used to altered/damaged specifically the bacterial membrane and/or bacterial Mechanism of Actions. Tables 7.5 (page 186, and 7.8 page 196) proteins Physical Methods WHAT is Moist Heat Stenilization and WHY is used WHAT is an Autoclave and WHICH Temperature, time and pressure Autoclaving. USES of Autoclaving. WHEN we use Milk Sterilization versus the C/time conditions used in both s are used to do Chemical Agents, WHEN we used Antiseptics and WHEN Disinfectants. Explain WHAT are they. Look at Table 7.7 Page 195 "Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria: COMPLETE the table by DRAWING the table in your essay and by adding es column between the first Type of Chemical Agent) and second column (Effect against Endospores For this new second column (that you will name Chemical Agent) you will write an example for the corresponding type. Example: (type column) #7 Bisphenols example. hexachlorophene. As you are organized properly. DEFINE by COMPARISON (chose pairs to compare) (At least the fist wo columans far the exercise to be valid) Antisepsis Sterilization Disinfection Pasteurization bacteriostatic Commercial Stenilization biocide Sanitization DegermingExplanation / Answer
Q3) Part a) The two categories of actions of microbial control agents that actually kill or inhibit microbes are i) physical methods ii) chemical methods.
Physical methods- Physical methods either kill microbes, or reduce their numbers in a solution, or on the surface of a fomite (objects or material which carry infection) .
Chemical methods - In this certain chemical agents are applied, they inhibit the growth or kill microbes on fomites or on the surface of skin. The selection of an appropriate technique is important, as many physical and chemical agents can damage the cells and tissues of the individual as well as the microbes.
Mechanism of action -
physical methods:- Physical methods are used since many years to kill or control microbial growth for food preservation, most commonly used methods are by application of high temperatures, radiation, filtration, and desiccation (drying), etc. Many of these methods nonspecifically kill cells by disrupting membranes, changing membrane permeability, or damage proteins and nucleic acids by denaturation, degradation, or by chemical modification.
Various physical methods used to kill microorganism are-
Heat:- Microorganisms have a minimum, an optimum, and a maximum temperature for growth. Temperatures below the minimum level makes the microorganisms static. They inhibit microbial growth by slowing down metabolism but do not kill the organism. Temperatures above the maximum level kills the microorganisms, because they denature microbial enzymes and other proteins.
At high Temperature Vegetative microorganisms are killed at temperatures 50°C - 70°C with moist heat. Bacterial endospores, are very resistant to heat and extended exposure to very higher temperature is required to kill them. High temperature is applied as either moist heat or dry heat. a. Moist heat is more effective to kill microorganisms because they can penetrate the microbial cells. Moist heat kills microorganisms by denaturing their proteins (it causes proteins and enzymes to lose their three-dimensional functional shape). It also melts lipids in cytoplasmic membranes.
Autoclaving - In this method steam is applied under pressure. Water has a boiling point of 100°C; but when it is put under pressure, it boils at a higher temperature. During autoclaving, the materials to be sterilized are placed under 15 pounds per square inch of pressure in a pressure-cooker type of apparatus. When placed under 15 pounds of pressure, the boiling point of water is raised to 121°C, this temperature is sufficient to kill bacterial endospores. The time the material is left in the autoclave varies depending on the nature and amount of material to be sterilized. Autoclaving kills both vegetative organisms and endospores if exposed for a longer time, and it is the most common method of sterilization for materials not damaged by heat. 2. Boiling water Boiling water (100°C) will usually kills vegetative cells after 10 minutes of exposure, but certain viruses, like hepatitis viruses,survive longer upto 30 minutes, and endospores of certain Clostridium and Bacillus species may survive for an hour .
Dry heat - It kills microorganisms by a process of protein oxidation. Examples of dry heat include: 1. Hot air sterilization. Microbiological ovens use very high dry temperatures around 171°C for 1 hour; 160°C for 2 hours or longer; or 121°C for 16 hours or longer based on the volume. They are usually used to sterilize glassware, metal instruments, and other inert materials like oils and powders which are not damaged by excessive temperature.
Incinerators -are used to destroy disposable materials by burning.
Pasteurization - It is a method used to heat milk and other materials to kill micro-organisms or pathogens.
Low temperature- It inhibits microbial growth by slowing down microbial metabolism. Examples are refrigeration and freezing. In refrigeration at 5°C slows the growth of microorganisms and keeps food fresh for a few days. In freezing at -10°C it stops microbial growth, but usually do not kill microorganisms, and keeps food fresh for several months.
Desiccation- It makes the microorganisms static. Lack of water inhibits the action of microbial enzymes. Dehydrated and freeze-dried foods, do not require refrigeration due to absence of water , that inhibits microbial growth.
Radiation - ultraviolet portion of the light spectrum has all radiations with wavelengths from 100 nm to 400 nm. It has low wave-length and low energy. The microbicidal activity of ultraviolet (UV) light depends on the length of exposure, the longer the exposure the greater the killing of microorganism. It also depends on the wavelength of UV used. The most destroying wavelengths of UV light is between 260 nm - 270 nm range , in this range it is absorbed by nucleic acid. The mode of action, is UV light is absorbed by microbial DNA and causes adjacent thymine bases on the same DNA strand to covalently bond together,as a result a thymine-thymine dimer is formed. As the DNA replicates, nucleotides do not complementary base pair with the thymine dimers and this terminates the replication of that DNA strand, most of the damage from UV radiation occurs when cell tryes to repair the damage to the DNA by a process called SOS repair. In very heavily damaged DNA containing large numbers of thymine dimers, a process called SOS repair occurs as a last effort to repair the DNA. In this process, a gene product of the SOS system binds to DNA polymerase allowing it to synthesize new DNA across the damaged DNA, but this altered DNA polymerase loses its proofreading ability and form a DNA which contains many misincorporated bases. In other words, UV radiation causes mutation and lead to faulty protein synthesis. With sufficient mutation, bacterial metabolism is blocked and the organism dies.
Chemical methods used to kill microorganisms are-
Chemical agents for the control of microbial growth are either microbiocidal or microbiostatic. Microbiocidal agents are sterilants they kill all living cells. Microbiostatic agents kill some cells and inhibit the growth of others. The spectrum of activity exhibited by any microbiocidal or microbiostatic agent is an important factor to choose the method.
There are various method of chemical control they are
Antibiotics - These are produced by microorganisms to kill or inhibit the growth of other microorganisma.These are usually selectively toxic, and can be naturally produced, synthesized.
Antiseptics - These are the synthetic compounds which kill or inhibt the growth of microbes on the surface of the skin.
Disinfectants - These are the chemical compounds which kill or inhibit microbes on the surface of fomites.
Preservatives, - These are sugars, salt, nitrates, nitrites, sulfate, and sulfites ,they inhibit microbial growth in food, usually by creating osmotic environments which is unfavorable for microbial growth. These is again subdivided as high, intermediate, or low level agents.
High-level germicides- They sterilize fomites, but are toxic to skin and mucus membranes.
Intermediate-level disinfectants and antiseptics- They kill and inhibit on fomites and skin, but are toxic to the user at medium to high concentrations. Examples are phenolics and halogens.
Low-level disinfectants- These are alcohols, hydrogen peroxide, heavy metals, and soaps they kill some microbes but inhibit the growth of many microorganisms.
High level germicides- These are usually alkylating agents, the mechanism here is microorganisms are killed by adding ethyl or methyl groups to nucleic acids or proteins. The agents are capable of killing vegetative cells, spores, and inactivating viruses.
Intermediate level disinfectant-
Halogens are a family of elements having high affinity for electrons. This affinity makes them reactive with biological molecules, and they disrupt enzyme activity, breaks down lipid structure, and produces oxidizing agents like single oxygen (O). Most commonly used halogens as disinfectants are chlorine and iodine.
Low level disinfectatnts- Hydrogen peroxide is a low-level disinfectant agent, when it is used in concentrations of 3% or lower, it is used as an antiseptic for the treatment of minor cuts and scrapes and as a bleaching agent. When placed on the surface of an injury, hydrogen peroxide bubbles by the release of the enzyme catalase from tissues, that breaks it down into water and oxygen. This breakdown releases the peroxide ion a strong oxidizing agent, and the water released provides hydroxide ions which breaks hydrogen from biological molecules. Obligate anaerobic microbes are usually sensitive to hydrogen peroxide, as they do not produce catalase and the rapid release of oxygen gas inhibits their growth.
Q part-b)
Moist heat usually more effective than dry heat for killing microorganisms due to its ability to penetrate microbial cells. Moist heat kills microorganisms by denaturing their proteins (causes proteins and enzymes to lose their three-dimensional functional shape). It also may melt lipids in cytoplasmic membranes.
Water at high pressure level is used in moist heat sterilization. Autoclave is the instrument in which this process is carried out. The temperature of the steam in this method is lower when compared with dry heat sterilization, but the high pressure helps with effective sterilization to take place.
The structural proteins and the organism’s enzymes are destroyed by moist heat. as a result microorganism is killed. Moist heat method is used for heat sensitive materials and materials through which steam is permeable. Culture media is also sterilized through moist heat sterilization. In moist heat sterilization, the most resistant spores requires a temperature of 121°C for 30 minutes.
Q-Part-C)
Autoclaving - In this method steam is applied under pressure. Water has a boiling point of 100°C; but when it is put under pressure, it boils at a higher temperature. During autoclaving, the materials to be sterilized are placed under 15 pounds per square inch of pressure in a pressure-cooker type of apparatus. When placed under 15 pounds of pressure, the boiling point of water is raised to 121°C, this temperature is sufficient to kill bacterial endospores. The time the material is left in the autoclave varies depending on the nature and amount of material to be sterilized. Autoclaving kills both vegetative organisms and endospores if exposed for a longer time, and it is the most common method of sterilization for materials not damaged by heat. Boiling water at (100°C) usually kills vegetative cells after 10 minutes of exposure, but certain viruses, like hepatitis viruses,survive longer upto 30 minutes, and endospores of certain Clostridium and Bacillus species may survive for an hour .Autoclave is used to sterilize materials.
Pasteurization is the mild heating of milk to kill pathogens. But It does not, kill all organisms. Milk is usually pasteurized by heating to 71.6°C for at least 15 seconds in the flash method or 62.9°C for 30 minutes in the holding method.
Sterilization of milk is heating milk at 300 degrees for several seconds.Sterilization destroys all germs, and enables the milk to be stored for long periods at room temperature.
Q part-d) Antiseptics are synthetic compounds which kill or inhibit the growth of microbes on the surface of the skin.Example-mercuric chloride.
Disinfectants are chemical compounds which kill or inhibit microbes on the surface of fomites(objects or materials which carry infection) Example- alcohol, soaps.
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