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1 Chapter 1 : Physical and Chemical Methods of Control Clinical Gate Chemical Methods of Control Most reduce the microbial populations to safe levels or remove pathogens from objects. An ideal disinfectant or antiseptic (chemical agent) kills microorganisms in the shortest possible time without damaging the material treated. Are you sure you want to delete this answer? Yes Sorry, something has gone wrong. Control of Microbial Growth The control of microbial growth is necessary in many practical situations, and significant advances in agriculture, medicine, and food science have been made through study of this area of microbiology. This control is affected in two basic ways: Control of growth usually involves the use of physical or chemical agents which either kill or prevent the growth of microorganisms. Agents which kill cells are called cidal agents; agents which inhibit the growth of cells without killing them are referred to as static agents. Thus, the term bactericidal refers to killing bacteria, and bacteriostatic refers to inhibiting the growth of bacterial cells. A bactericide kills bacteria, a fungicide kills fungi, and so on. In microbiology, sterilization refers to the complete destruction or elimination of all viable organisms in or on a substance being sterilized. There are no degrees of sterilization: Sterilization procedures involve the use of heat, radiation or chemicals, or physical removal of cells. Methods of Sterilization Heat: For sterilization one must consider the type of heat, and most importantly, the time of application and temperature to ensure destruction of all microorganisms. Endospores of bacteria are considered the most thermoduric of all cells so their destruction guarantees sterility. Used for needles, inoculating wires, glassware, etc. Kills everything except some endospores. These two variables are extremely important. Higher temperatures ensure more rapid killing. Longer times are needed for larger loads, large volumes of liquid, and more dense materials. Autoclaving is ideal for sterilizing biohazardous waste, surgical dressings, glassware, many types of microbiologic media, liquids, and many other things. However, certain items, such as plastics and certain medical instruments e. When proper conditions and time are employed, no living organisms will survive a trip through an autoclave. Dry heat hot air oven: The rules of relating time and temperature apply, but dry heat is not as effective as moist heat i. Page 1

2 Chapter 2 : Importance of Bacteria in different Field with Physical & Chemical Control Physical methods for controlling the growth of microorganisms can be divided into heat methods and nonheat methods. The lowest temperature at which all microorganisms are killed in 10 minutes is the thermal death point, while the minimum amount of time required to kill microorganisms at a given. Has residual effect lasts a long time. Kills enveloped viruses but not naked viruses. Dilutions of household bleach between 1: Often found as a tincture or alcohol solution. Also found as an iodophor betadinetm where the iodine is complexed with an organic molecule. Iodophors are more stable than tinctures and they release iodine more slowly and steadily. Therefore they are less harmful to human tissue. These are weak antiseptics which are active against a wide variety of vegetative bacteria. They are not tuberculocidal. They are not sporocidal. They do not kill Pseudomonas. They are sporocidal and therefore sterilizing. Formaldehyde and glutaraldehyde are used to fix and preserve infectious tissues. These are also known to be carcinogens. Ethylene oxide is used in gas sterilizers. This is a very noxious, explosive gas. In ancient times copper and silver containers were used to preserve water. Merthiolate, mercurochrome, silver nitrate and copper sulfate are all used as antiseptics. Silver nitrate has long been used to prevent neonatal gonorrheal opthalmia and in the treatment of burns. This disinfectant is not sporocidal nor tuberculocidal. The catalase in human tissue neutralizes H2O2 however the generation of oxygen bubbles helps to clean out wounds and is strongly inhibitory to anaerobic bacteria. Page 2

3 Chapter 3 : An Overview to Control of Microorganisms - Biology LibreTexts methods of handling microbial cultures, patient specimens and other sources of microbes in a way that prevents infection of handler and others who may be exposed. Decontamination the removal or neuralization of an infectious, poisonous or injurious agent from a site. Methods of Microbial Control With the advent of the germ theory of disease, it became obvious that disease could be spread by organisms too small for the eye to see. In time, hospitals, clinics, and laboratories began to adopt these methods and improve upon them. Methods used to control the growth of microbial growth can be placed into two broad categories, physical and chemical. Physical methods either exclude microbes, or reduce their numbers in a solution, or on the surface of a fomite any nonliving material which might come into contact with the individual. Chemical methods involve the application of specific chemical agents which inhibit growth or kill microbes on fomites or the surface of skin. The selection of an appropriate technique is important, since many physical and chemical agents can cause damage to the cells and tissues of the individual as well as the microbe. Agents of microbial control either sterilize or disinfect. Sterilizing agents kill all living things, thus removing the living source of contagion. Disinfecting agents kill some microbes, but inhibit the growth of others. Most techniques only provide disinfection. These include population size, susceptability of the microorganism to the agent, concentration of the dose used, and the duration of treatment. Filtration Filtration is the passing of either a solution or gasses through a device which traps microbes on one side of a container or space, preventing them from passing to the other. Filters are materials which have pores openings of varying sizes. Particulate matter larger than the pore size in a filter is excluded from passage and is this physically excluded. The earliest form of filter used in microbiological was cotton, a fiberous material derived from plants. Cotton fibers form a densely packed matrix which offers a torturous path for particulate matter containing microbes to pass, while still allowing air to do so. This is only true however, as long as a cotton plug, filter, or bandage remains dry, since water clings to each fiber allowing microbes unrestricted access. In most cases, cotton has been replaced as a filter by ceramic filters and synthetic plastics such as nitrocellulose which offer very small pore sizes 0. Since these materials are not fiberous, all but the very smallest microbes can be removed from a solution passing through them. This solution, called a filtrate, is generally free from contaminants so long as the original pre-filtered solution did not contain organisms such as mycoplasma bacteria or viruses, both of which are smaller than most filters. As a consequence, filtration should be considered an agent of disinfection rather than sterilization. Dessication Dessication drying is the removal of moisture from the body of an organism. Many bacteria are very sensitive to water loss and can be killed simply by removal of water. For example, Treponema pallidum, the agent of syphillis, is so intolerant to water loss that it will die within twenty seconds on the surface of a dry fomite. The physical preservation of foodstuffs by drying has been practiced by humans for thousands of years and in most cases does reduce the number of potentially pathogenic microbes. One process, called lyophilization or freeze-drying, is used to rapidly remove water from the body of an organism under very cold temperatures in a partial vacuum. This process does not kill organisms such as bacteria, but does inactivate their metabolic processes. Lyophilization is used to preserve living bacterial cultures for storage and transport. To restore the freeze-dried cells, an individual has only to rehydrate them in a nutrient broth solution and incubate the culture at the optimum temperature for growth of the microbe. It is important to note, however, that not all microbes are killed or inactivated by dessication. Bacteria which form spores such as members of the genera Bacillus and Clostridium, cyst-forming protists, and viruses can withstand drying, simply becoming inactive until moisture becomes available. For this reason, dessication can only be considered a form of disinfection. Radiation Radiation describes a physical phenomenon which occurs when matter releases either energy, atomic particules, or both. Radiation can affect the chemical makeup of the cell by altering or disrupting the structure of biological molecules. Ionizing radiation strips electrons away from biological molecules. Both gamma and Page 3

4 X-radiation are ionizing forms. Ultraviolet radiation is absorbed by the pyrimidine bases cytosine and thymine in DNA. When two thymine or cytosine molecules lie adjacent to one another on a nucleoside, ultraviolet radiation with wavelengths between nm and nm causes them to have a greater affinity for one another than for their complementary adenines on the opposite nucleoside. The two bond together, forming a dimer, which disrupts the normal sequence of nucleotide bases. This kind of mutation prevents the cell from producing proteins which may be necessary for normal metabolism to occur. Some cells can repair this damage if exposed to visibile light through a process called photoreactivation light repair, wherein the dimer is nicked by a restriction endonuclease, then cut away and replaced by DNA polymerase. The new thymine or cytosine bases are then bonded to their complementary adenines or guanines by DNA ligase. Since light repair can occur, the use of ultraviolet radiation has only disinfecting activity and cannot be considered a sterilizing agent. Temperature Excess heat energy can cause proteins to become denatured, meaning that they lose their normal three-dimensional shape. Effective temperature for the reduction of microbes is measured as the thermal death point TDP of each organism, which is the temperature at which all growth stops. Thermal death time TDT is the amount of time it takes to kill all of the microbes in a sample, and the decimal reduction factor DRF is the amount of time at a specific heat necessary to reduce the population of microbes in a sample tenfold. The most common methods of applying excess heat energy are flaming and incineration, which completely destroy all life. Flaming of inoculating loops and needles, as well as the tops of glass culture tubes and flasks insures that no contaminating microbes can infect sterile media. Applying dry heat by forcing hot air onto the surface of an object can be used in a similar fashion, though many spore formers are capable of withstanding this. The application of moist heat, such as boiling, steaming, and pasteurization application of high heat to a solution for a short period of time, is also commonly used. These methods work well for most microbes, but are incapable of killing organisms which are thermoduric capable of withstanding elevated temperatures, or are spore formers. For example, the spores of Clostridium botulinum, the bacterium which causes botulism, can be boiled for up to five hours and still remain viable. The most effective application of moist heat is through the use of a device called an autoclave. The autoclave works on the principle of saturated steam. The steam strikes the surface of the object to be sterilized and condenses into water as its excess heat energy is released. This condensation creates a partial vacuum which draws more steam to the object. Saturated steam is extremely effective as a sterilizing agent, at least times more effective than the application of dry heat. Autoclaves are usually operated in cycles between 15 and 90 minutes, and can be used to sterilize glassware, surgical implements, soil, water, and microbiological media such as broths and agars. They cannot, however, be used to sterilize hydrophyllic powders which would clump, or hydrophobic oils since microbes suspended in oils would only be subjected to dry heat. Also, while contaminated bandages can be placed in an autoclave, the toxins or exoenzymes left behind by killed microorganisms such as Clostridium perfringens the agent of gas gangrene may still be capable of causing host cell damage, so these should be rinsed thoroughly with sterile water prior to reuse. All of the above physical means of control can be checked for effectiveness utilizing various bacteria as quality control agents. Devices which emit ionizing radiation can be tested with Micrococcus radiouridans, U. These organisms are generally supplied to laboratories live or in ampules or tape strips, which can be placed in the control device. After a normal operating cycle, the organisms are incubated in microbiological media. If growth occurs, the device is not operating properly and should be repaired. Quality control checks and maintenance are vital to the effective microbiological laboratory or health-care facility, and should be performed on a regular basis to prevent contamination and the spread of disease. Chemical Methods Chemical agents for the control of microbial growth are either microbiocidal or microbiostatic. Microbiocidal agents are sterilants which 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 in choice, and should be considered, along with potential harmful effects on the user. An agent which kills staphylococci may be totally ineffective against mycobacteria, and would be useless in a tuberculosis ward. Also, a broadly killing sterilant may release gasses which are toxic to Page 4

5 patients and staff. Most often, chemical agents which disinfect are utilized by clinics, hospitals, and laboratories. While these agents do not sterilize, their toxicity is usually much less than that of a sterilant, and prevention of infection is stressed. There are four large categories for agents of chemical control. Antibiotics are produced by microorganisms to kill or inhibit the growth of other microbes. These agents are generally selectively toxic, and can be naturally produced, synthesized, or or semisynthetic. Antiseptics are synthetic compounds which kill or inhibt the growth of microbes on the surface of the skin. Disinfectants are chemical compounds which kill or inhibit microbes on the surface of fomites. Preservatives, such as sugars, salt, nitrates, nitrites, sulfate, and sulfites inhibit microbial growth in food, usually by producing osmotic environments which are unfavorable to microbial growth. These can be further subdivided as high-, intermediate, or low level agents. High-level germicides sterilize fomites, but are toxic to skin and mucus membranes. Intermediate-level disinfectants and antiseptics kill and inhibit on fomites and skin, but can be toxic to the user at medium to high concentrations. Examples include phenolics and halogens. Low-level disinfectants, such as alcohols, hydrogen peroxide, heavy metals, and soaps kill some microbes but inhibit the growth of most. High-Level Germicides These are called agents of cold sterilization, since no heat needs to be applied to increase their activity. These are generally alkylating agents, which kill by adding ethyl or methyl groups to nucleic acids or proteins. While the agents are capable of killing vegetative cells, spores, and inactivating viruses, some take up to several hours to complete their germicidal activity. Aldehydes, such as formaldehyde and gluteraldehyde, fix tissues by alkylating and forming cross-links between adjacent proteins. They are commonly used as fixitive compounds for electron microscopy, preservatives of specimens and cadavers, in some synthetic plastic compounds, and can be used to sterilize anesthesia tubing and surgical implements. Aldehydes can fix living tissues such as mucus membranes and have the ability to vaporize or outgas from compounds containing them, so they should be handled with caution. It is generally used to sterilize bone used in grafts. It quickly breaks down into nontoxic compounds when it comes into contact with organic matter, but can burn skin. Ethylene oxide carboxide kills vegetative cells and spores. It is a liquid at temperatures below It is generally used in a chamber similar to an autoclave at 60o C for hours, where it is mixed in a 9: Carboxide can be used to sterilize surgical implements and glassware, but these fomites must be allowed to degass before use, since residues can stimulate mutations in bacteria. Ozone O3 occurs naturally in the upper atmosphere, where it serves to shield the surface of the earth from solar radiation, and is produced as an exhaust gas by vehicles and industry, acting as a pollutant in the lower atmosphere. Applied properly in a chamber, ozone is a powerful oxidizing agent which kills cells and spores on the surface of glassware, surgical implements, and bandages. Page 5

6 Chapter 4 : Physical And Chemical Control Of Microbial Growth Flashcards by ProProfs Methods used to control the growth of microbial growth can be placed into two broad categories, physical and chemical. Physical methods either exclude microbes, or reduce their numbers in a solution, or on the surface of a fomite (any nonliving material which might come into contact with the individual). Microorganisms are controlled by means of physical agents and chemical agents. Physical agents include such methods of control as high or low temperature, desiccation, osmotic pressure, radiation, and filtration. Control by chemical agents refers to the use of disinfectants, antiseptics, antibiotics, and chemotherapeutic antimicrobial chemicals. In this unit we will concentrate on the chemical control of microbial growth with a special emphasis on the antibiotics and chemotherapeutic antimicrobial chemicals used in treating bacterial infections. Control of microorganisms by means of physical agents will be covered in Lab 18 and control by means of disinfectants, antiseptics, and sanitizers will be discussed in Lab The basis of chemotherapeutic control of bacteria is selective toxicity. Selective toxicity means that the chemical being used should inhibit or kill the intended pathogen without seriously harming the host. A broad spectrum agent is one generally effective against a variety of Gram-positive and Gram-negative bacteria; a narrow spectrum agent generally works against just Gram-positives, Gram-negatives, or only a few bacteria. As mentioned above, such agents may be cidal or static in their action. There are two categories of antimicrobial chemotherapeutic agents: Antibiotics are metabolic products of one microorganism that inhibit or kill other microorganisms. Chemotherapeutic synthetic drugs are antimicrobial drugs synthesized by chemical procedures in the laboratory. Why then do bacteria produce antibiotics? There is growing support for multiple actions for microbial antibiotic production: If produced in large enough amounts, antibiotics may be used as a weapon to inhibit or kill other microbes in the vicinity to reduce competition for food. Antibiotics produced in sublethal quantities may function as interspecies quorum sensing molecules enabling a number of different bacteria to form within a common biofilm where metabolic end products of one organism may serve as a substrate for another. All the organisms are protected within the same biofilm. Antibiotics produced in sublethal quantities may function as interspecies quorum sensing molecules enabling some bacteria to manipulate others to become motile and swim away thus reducing the competition for food. Antibiotics action may result in the degradation of bacterial cell walls or DNA and these products can act as cues that trigger other bacteria to produce a protective biofilm. Antibiotics produced in sublethal quantities may trigger intraspecies quorum sensing. Exposure to low concentrations of an antibiotic may trigger bacteria to produce quorum sensing molecules that trigger the population to produce a protective biofilm. The biofilm then protects the population from greater concentrations of the antibiotic. Summary Physical control includes such methods of control as high or low temperature, desiccation, osmotic pressure, radiation, and filtration. Chemical control refers to the use of disinfectants, antiseptics, antibiotics, and chemotherapeutic antimicrobial chemicals. Sterilization is the process of destroying all living organisms and viruses. Disinfection is the elimination of microorganisms, but not necessarily endospores, from inanimate objects or surfaces. Decontamination is the treatment of an object or inanimate surface to make it safe to handle. A disinfectant is an agents used to disinfect inanimate objects but generally to toxic to use on human tissues. An antiseptic is an agent that kills or inhibits growth of microbes but is safe to use on human tissue. A sanitizer is an agent that reduces microbial numbers to a safe level. An antibiotic is a metabolic product produced by one microorganism that inhibits or kills other microorganisms. Synthetic chemicals that can be used therapeutically. An agent that is cidal in action kills microorganisms. An agent that is static in action inhibits the growth of microorganisms. A broad spectrum agent is one generally effective against a variety of Gram-positive and Gram-negative bacteria. A narrow spectrum agent generally works against just Gram-positives, Gram-negatives, or only a few bacteria. Glossary Basic terms used in discussing the control of microorganisms include: Sterilization Sterilization is the process of destroying all living organisms and viruses. A sterile object is one free of all life forms, including bacterial Page 6

7 endospores, as well as viruses. Disinfection Disinfection is the elimination of microorganisms, but not necessarily endospores, from inanimate objects or surfaces. Decontamination Decontamination is the treatment of an object or inanimate surface to make it safe to handle. Disinfectant A disinfectant is an agents used to disinfect inanimate objects but generally to toxic to use on human tissues. Antiseptic An antiseptic is an agent that kills or inhibits growth of microbes but is safe to use on human tissue. Sanitizer A sanitizer is an agent that reduces microbial numbers to a safe level. Antibiotic An antibiotic is a metabolic product produced by one microorganism that inhibits or kills other microorganisms. Chemotherapeutic synthetic drugs Synthetic chemicals that can be used therapeutically. Cidal An agent that is cidal in action will kill microorganisms and viruses. Static An agent that is static in action will inhibit the growth of microorganisms. Page 7

8 Chapter 5 : Chemical Methods of Control For thousands of years, humans have used various physical methods of microbial control for food blog.quintoapp.com control methods include the application of high temperatures, radiation, filtration, and desiccation (drying), among others. They play very important role in the life of human beings. Their importance is given below: Ecological Importance Bacteria are ecologically very important. They show many adaptations. So they are present everywhere. They decompose organic matter and play an important role in the completion of cycles of nitrogen, phosphorus, sulfur and carbon. Economic Importance Bacteria show following beneficial and harmful effects: Bacteria are used in number of industries like food, drugs production of antibiotics and vaccines and biotechnology. They are responsible for the spoilage of food and vegetables. Many plant pathogens adversely affect the agriculture the agriculture industry. Bacteria are common pathogen of humans. There are species of bacteria which cause disease in man. Many bacteria normally live in the bodies of man and other animals and perform important functions. Medical Importance Bacteria are very common pathogens of humans. Approximately, species are known to cause diseases in humans. Many bacteria normally inhabit the bodies of man and other animals. Decaying of dead bodies: Bacteria decompose the dead remains of plants, animals and human beings into simpler compounds. In this way they help to clean the world. Bacteria are used in dairy industry they change the milk into curd. They are used in the formation of butter and cheese from milk. From certain bacteria antibiotics are obtained, for example Terramycin, Streptomycin, Neomycin etc. Bacteria are used in the preparation of alcohol and vinegar. Bacteria are also used in leather industry. Certain bacteria are present in the intestine of man arid help in the digestion of cellulose. Bacteria increase the fertility of soil by adding organic substances due to the decompositions of dead bodies. Bacteria also take part in nitrogen fixation i. These compounds are used by the plants. Bacteria spoil our food stuff in large amount by the chemical process. It is a great loss. Bacteria are responsible to cause various diseases in man and other animals, such as Tuberculosis T. Bacteria also cause disease in various plants, such as Citrus Canker, Fire blight of apple, Ring disease of potato, wilt of solanaceae plants etc. Control of Bacteria It is necessary to control bacteria in home, in industries and in medical fields. The disease can be prevented by controlling the bacteria. The control of bacteria can prevent the spoilage of foods and other industrial products. Microorganisms can be controlled by following methods: Physical Methods The process in which we use physical methods to control bacteria is known as sterilization. Steam, dry heat, gas, filtration and radiations are used in process of sterilization. Sterilization destroys all the microorganisms. Following methods are used for sterilizations: High temperature is used in microbiological labs for the controlling of microbes. Both dry and moist heat is effective. Moist heat causes coagulation of proteins that kill the microbes. Dry heat causes the oxidation of chemical compounds of the microbes and kills them. Certain electrochemical radiations below nm are effective for the killing of bacteria. Gamma rays are used for the sterilization process. Membranous filters can sterilize the heat sensitive compounds like antibiotics, serum and hormone etc. Chemical Methods Antiseptics, disinfectants and chemotherapeutic agents can be used for microbial control. Chemical substances used on living tissues outside the body that inhibit the growth of microorganism are called antiseptics. Antiseptics are mostly used on wounds. The chemical agents used on non-living material surgical instrument etc. The important chemical agents used for disinfection are oxidizing and reducing agents. For example halogens chlorine, phenols, hydrogen peroxide, potassium permagnate, alcohol and formaldehyde etc. Chemotherapeutic agents and antibiotics: They destroy or inhibit the growth of microorganisms in the living tissues. They work with the natural defense and stop the growth of bacteria and other microbes. Sulfonamides, tetracycline, penicillin, etc. Brief note on Control of Bacteria The different methods to control the infections of micro-organisms are as follows: Infected persons should be properly treated by effective medicines. Persons in a population should be treated by immunization and vaccination. In epidemic condition the infected persons Page 8

9 should be kept in quarantine to avoid the spread of infection to healthy persons. At different possible stages the life cycle of pathogen should be disrupted, so it cannot cause the infection. The host bodies of pathogen should be identified and treated well to control the disease. By different ways knowledge and awareness about diseases and infection of pathogen should be provided to the public. Many methods should be used to kill or inhibit the infection of pathogens, such as: With the help of antiseptics. By the use of antibiotics. By chemotherapy chemical treatment. Page 9

10 Chapter 6 : FAQ: Physical and Chemical Control of Microorganisms this physical control is a passage of fluid (liquid or gas) through a sieve designed to trap particles (cells or viruses) and separate them from the fluid filtration this method of physical control uses a vacuum to assist the movement of fluid through the filter. Should I use consumer products with antibiotics? The process known as sterilization refers to the process in which all living cells, spores, and viruses are completely destroyed or removed from an object or environment. Once something is sterilized, it will remain sterile if properly sealed. Sterilization is performed on surgical equipment, needles, and certain lab equipment in order to prevent the spread of microorganisms. Autoclaves are devices which use hot steam under high pressure to sterilze objects. Sterilization is an extreme level of cleanliness that is usually not required outside of a medical, industrial, or laboratory environment. In everyday environments, disinfection of objects is considered a more practical option. The process known as disinfection is the killing, inhibition, or removal of microorganisms that cause disease. Disinfection may not necessarily eliminate spores or all of the microorganisms from an object or environment. While disinfection is not as extreme as sterilization, but it is considered to be an adequate level of cleanliness for most situations. Pasteurization is a process used in preserving heat sensitive foods such as milk, beer, and other beverages. Pasteurization is not a method of sterilzation, which is why pasteurized foods will eventually spoil if given enough time. Milk that has been treated in this way can be kept at room temperature for 2 months with only minimal changes in flavor. Disinfectants are chemical agents used to disinfect inanimate objects and surfaces. Examples of disinfectants include iodine solution, copper sulfate, ozone, and chlorine gas. Antiseptics are chemical agents applied to living tissues to prevent infection. Antiseptics are generally less toxic than disinfectants because they must not cause too much damage to the host living tissue. The concentration of a chemical agent can determine if it can be used as a disinfectant or an antiseptic. In the case of iodine, weaker solutions of iodine can be used for antiseptic purposes, while stronger concentrations should be used as a disinfectant. Moisture improves heat penetration, making sterilization by moist heat more effective then dry heat. Killing microorganisms by dry heat is a lengthy process that requires high temperatures. These conditions are not sufficient to inactivate mold or bacteria spores, which are more heat-resistant than cells in their vegetative states. The "gold standard" for heat sterilizatin is inactivation of Bacillus stearothermophilus spores. If heat treatment was sufficient to inactivate test strips containing these spores, then the sterilization is considered successful. It is important to note that there are rare types of bacteria which are capable of growing at high temperatures. These bacteria are classified as thermophiles and hyperthemophiles. Bacillus stearothermophilus is a thermophile. These organisms normally growth in unusually hot environments, including hot springs and deep-sea vents. Clearly sterilization by heat may not be the most efficient method to eliminate these types of bacteria, but they are almost never found in common environments. Proper cooking requires that the temperature at the centre of the meat reaches the following temperatures: Page 10

11 Chapter 7 : Discuss five 5 physical or chemical methods of microbial control? Yahoo Answers Microbial control can be achieved by physical methods, chemical agents, or a combination of both. Under ideal circumstances the methods used for microbial control should be inexpensive and fast-acting. Microbial Products Chemical Methods of Control Chemical agents are generally not intended to achieve sterilization. Most reduce the microbial populations to safe levels or remove pathogens from objects. An ideal disinfectant or antiseptic chemical agent kills microorganisms in the shortest possible time without damaging the material treated. Among the important criteria for selecting an antiseptic or disinfectant are the concentration of disinfectant to be used, whether the agent is bactericidal or bacteriostatic, the nature of the material to be treated, whether organic matter will be present, the temperature and ph at which the chemical agent will be used, and the time available in which the chemical agent will be left in contact with the surface tested. A phenol coefficient PC greater than one indicates that the chemical agent is more effective than phenol and less than one that it is less effective. Various dilutions of the chemical agent are made and tested against a standardized preparation of test bacteria on the type of material later to be disinfected in normal use. First used by Joseph Lister in the s, it is the standard for most other antiseptics and disinfectants. The phenolics damage cell membranes and inactivate enzymes of microorganisms, while denaturing their proteins. Figure 1 A selection of chemical disinfectants and antiseptics. It persists on the skin and is effective against vegetating bacteria, but not spores. They include Betadine and Isodyne, both of which contain a surface active agent called povidone. Iodine combines with microbial proteins and inhibits their function. It is used as sodium hypochlorite bleach. As calcium hypochlorite, chlorine is available to disinfect equipment in dairies, slaughterhouses, and restaurants. The chloramines contain chlorine together with ammonia. They are used to sanitize glassware and eating utensils and are effective in the presence of organic matter. Chlorine is also used as a gas to maintain a low microbial count in drinking water. It is also used to cauterize wounds. Zincis useful as zinc chloride in mouthwashes and as zinc oxide as an antifungal agent in paints. The heavy metals are believed to act by combining with sulfhydryl groups on cellular proteins. Soaps and detergents decrease the surface tension between microorganisms and surfaces, and thereby help cleanse the surface. They solubilize the cell membranes of microorganisms. It is widely employed for embalming purposes. This chemical denatures proteins and destroys all microorganisms, including bacterial spores. It is used at warm temperatures in an ethylene oxide chamber. Several hours are needed for exposure and flushing out the gas, which can be toxic to humans. Propylene oxide, a similar compound, is also valuable as a sterilant. Hydrogen peroxide is useful on inanimate objects and in foods, but on the skin surface, it is quickly broken down by the enzyme catalase, liberating oxygen. This oxygen causes a wound to bubble and thereby removes microorganisms present. However, the chemical activity on the skin is limited compared to that on inanimate surfaces. Contact lenses can be disinfected with hydrogen peroxide. Benzoyl peroxide is applied to the skin to treat acne due to anaerobic bacteria. The oxygen released by the compound inhibits anaerobic growth. Ozone can be used to disinfect water, where it oxidizes the cellular components of contaminating microbes. Sorbic acid is used in a number of acidic foods, including cheese, to prevent microbial growth. Benzoic acid also inhibits fungi and is used in acidic foods and soft drinks. Calcium propionic acid prevents the growth of mold in breads and bakery products. Chapter 8 : Control of Microorganisms Control of microorganisms is essential in order to prevent the transmission of diseases and infection, stop decomposition and spoilage, and prevent unwanted microbial contamination. Microorganisms are controlled by means of physical agents and chemical agents. Page 11

12 Chapter 9 : Control of Microbial Growth Usually we mean negative control and the rest of this discussion relates to the destruction or inhibition of microbes: PHYSICAL AND - see Tortora et. al. for terms. When disinfecting, one must be concerned with the most resistant life forms present. Page 12