Chapter 20-Microbial Growth Control
制药用水水系统设计-消毒方式的比较
DNA (脱毎核勰核酸)所吸收,从而破坏
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口、八mn丈貝叩、寻匕岌.珂眾祖：LH
八仕匕。num刘：貝穴 最入吸收峰.
用水系统而言，巴氏消毒常指低温灭菌。
2.
经典的巴氏消毒主要使用在食品工业中对牛奶进行消毒处理，在杀灭牛奶中的结 核 菌的同时，保留了牛奶中对人体生长所需的维生素的蛋白质，使牛奶成为安全 的营养
品，各牛奶进行巴氏消毒的程序与一般无菌产品的灭菌程序相仿，所不同 的是温度较
彳氐，时间技长，通常先将牛奶加热到80°C,停留一定时间，进行消毒, 完成消毒后，
, UV Intensity (mW/cm2). • Dose = UV Intensity (mW/cm2) x time (s) =mWs/ciri2 = mJ/cm2
4
紫外线强度剂量
What UV doses are used for disinfection and oxidation?
・ Waste water disinfection: 30 mJ/cm2
Hg Low pressure Lamp 254 nm_
780 Wavelength (nm)
4
RF
紫外线杀菌作用
紫外线杀菌原理
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uz/\ j 飒物站依徵 an I 毎 阕.洒毋髭部 浆
殖的基础.UVC中240nm-2g0nm紫外线能被DNA
微生物学英文-ControllingMicrobes
– kills endospores
• Pasteurization
– kills certain microorganisms
– Bacteria
Fungi
Spores
5-10 min. 60-70oC
5-10 min.
5-10 min.
50-60oC 70-80oC
© 2004 Wadsworth – Thomson Learning
– minimal time – kill all microorganisms (sterilize)
• liquid suspension
– at given temperature
© 2004 Wadsworth – Thomson Learning
Conditions that Affect Antimicrobial Activity
© 2004 Wadsworth – Thomson Learning
Decimal Reduction Time
• Example: 1,000,000 (106) • 1 minute = 90% killed • 2 minutes = 100,000 (90%) • 3 minutes = 10,000 • 4 minutes = 1,000 • 5 minutes = 100 • 6 minutes = 1 cell
© 2004 Wadsworth – Thomson Learning
Microbial Death Rate
• Decimal reduction time
– D-value – time required to kill
90% of cells
• Heat treatments
Chapter 20(1)
Antiseptics, Disinfectants, and Sterilants
Antiseptics: chemical agents that kill or inhibit growth of microorganisms and are nontoxic enough to be applied to living tissues.
Chapter 20 Microbial Growth Control
Endospores
Heat sterilization procedures are designed to destroy endospores.
A major factor in the resistance of endospores is the amount and state of water they contain (minimal amounts and becomes gel-like).
Disinfectants (germicides): chemicals that kill microorganisms and are used on inanimate objects.
Sterilants: disinfectants that can kill all microbial life and are used to sterilize inanimate objects and surfaces.
Antimicrobial agents: natural or synthetic chemical that kills or inhibits the growth of microorganisms.
化生专业微生物-第7章-微生物的生长(上传)
2、液体培养法（in liquid medium）
好氧菌的浅盘培养（shallow pan cultivation） 深层液体培养—— 发酵罐（fermenter）
Chapter7-3-环境对微生） 生长是微生物与外界环境因素共同作 用的结果。环境条件的改变，在一定限度 内，可引起微生物形态、生理、生长、繁 殖等特征的改变。当环境条件的变化超过 一定极限，则导致微生物的死亡。
高层琼脂柱、厌氧培养皿、Hungate滚管
技术、厌氧罐（anaerobic jar）技术、
厌氧手套箱（anaerobic glove box） 。
2、液体培养（in liquid medium）
（1）好氧菌（aerobes）
氧的供应是好氧菌生长繁殖的限制因 子，为保证溶解氧浓度，必须增加培养液 和氧的接触面或提高氧分压：浅层培养； 振荡培养；深层液体培养器的底部通入加 压空气；对培养液进行机械搅拌。
主要因素：营养条件、理化因素、生物因素
一、温度（Temperature）
不同微生物的生长温度范围有宽有 窄，但都有最低生长温度，最适生长温
度，最高生长温度这3个重要指标，即生
长温度三基点（three cardinal point）。
把微生物作为一个整体来看，其温
度的三基点极其宽。
根据生长温度的范围，可把微生物
生长曲线（Growth curve）：定量描述液体 培养基中微生物群体生长规律的实验曲线。
把少量纯种单细胞微生物接种到定量的液体培 养基中，定时取样测定细胞数量，以培养时间为横 座标，以菌数的对数为纵座标作图，得到的一条反
映细菌在整个培养期间菌数变化规律的曲线。
根据微生物的生长速率常数，生长曲线可以分为： 延滞期，对数期，稳定期和衰亡期等4个生长时期
北京大学 微生物 第九讲微生物的生长及其控制
Exponential Phase（指数期） （指数期） 是在生长曲线中， 是在生长曲线中，紧接着延滞期的一段细胞数以几何 级数增长的时期。 级数增长的时期。 特点： 特点： 1. 生长速率的常数最大，倍增时间最短 生长速率的常数最大， 2. 细胞进行平衡生长，菌体各部分的成分十分均匀 细胞进行平衡生长， 3. 酶系活跃，代谢旺盛 酶系活跃，
第四节 有害微生物的控制 Growth Control
Definitions: 灭菌 Sterilization – the process of destroying all forms of microbial life on an object or in a material. 消毒 Disinfection – the process of destroying vegetative pathogens but not necessary endospores. 防腐 Antisepsis – chemical disinfection of skin, mucous membranes or other living tissues 化疗 chemotherapy
磺胺的作用机制
磺胺的结构与细菌的一种生长因子（合成四氢叶酸） 磺胺的结构与细菌的一种生长因子（合成四氢叶酸） 生长因子 四氢叶酸 -----对氨基苯甲酸（PABA)高度类似。 对氨基苯甲酸（ 高度类似。 对氨基苯甲酸 高度类似 磺胺增效剂 三甲基苄二氨嘧啶--增效剂---三甲基苄二氨嘧啶 （磺胺增效剂 三甲基苄二氨嘧啶 TMP ） 具体的反应过程（ 具体的反应过程（p181) 酶一 酶二 酶三 前体 二氢蝶叮====二氢蝶酸 二氢蝶酸===二氢叶酸 二氢叶酸===四氢叶酸 四氢叶酸-------一碳基转移 二氢蝶叮 二氢蝶酸 二氢叶酸 四氢叶酸 一碳基转移 PABA
chapter_7_the_control_of_microbial_growth
Chapter 7The Control of Microbial GrowthLearning Objectives1. Define the following key terms related to microbial control: sterilization, disinfection, antisepsis,germicide, bacteriostasis, asepsis, degerming, and sanitation.2. Describe the patterns of microbial death caused by treatments with microbial control agents.3. Describe the effects of microbial control agents on cellular structures.4. Know about the efficacy of moist heat (boiling, autoclaving, and pasteurization) and dry heat.5. Know how filtration, low temperature, desiccation, and osmotic pressure suppress microbial growth.6. Know how radiation kills cells.7. Know how microbial growth is affected by the type of microbe and the environmental conditions.8. List the factors related to effective disinfection.9. Identify the methods of action and preferred uses of chemical disinfectants.10. Know the advantage of glutaraldehyde over other chemical disinfectants.11. Identify the method of sterilizing plastic labware.12. Explain how microbial control is affected by the type of microbeThe Terminology of Microbial Control(Table 7.1)1. The control of microbial growth can prevent infections and food spoilage.2. Sterilization is the process of destroying all microbial life on an object.3. Commercial sterilization is heat treatment of canned foods to destroy C. botulinum endospores.4. Disinfection is the process of reducing or inhibiting microbial growth on a nonliving surface.5. Antisepsis is the process of reducing or inhibiting microorganisms on living tissue.6. The suffix -cide means to kill; the suffix - stat means to inhibit.7. Bacterial contamination is sepsis.The Rate of Microbial Death1. Bacterial populations subjected to heat or antimicrobial chemicals usually die at a constant rate. This isgraphed as a death curve.2. Such a death curve, when plotted logarithmically, shows this constant death rate as a straight line (Fig.7.1).3. The time to kill a microbial population is proportional to the number of microbes.4. Factors affecting microbial control by physical and chemical methods include:A. Microbial species (their characteristics) and life cycle phases (i.e., endospores) have differentsusceptibilities to physical and chemical controls.B. Organic matter may interfere with heat treatments and chemical control agents.C. Longer exposure to lower heat can produce the same effect as shorter time at higher heat.D. Type and concentration of agent used also affect the efficacy of microbial control. Some agents,for example the preservative sodium benzoate, do not work at physiological pH. The pH needsto be lowered for them to be effective.E. Number of microbes present affect the efficacy of antimicrobial process or agent. A highmicrobial load may require more time of exposure and/or a greater concentration ofantimicrobial agent.Actions of Microbial Control Agents (Ways of killing or inhibiting microbes) Alteration of Membrane Permeability1. The susceptibility of the plasma membrane is due to its lipid and protein components.2. Certain chemical control agents damage the plasma membrane by altering its permeability. Damage to Proteins and Nucleic Acids1. Some microbial control agents damage cellular proteins by breaking hydrogen and covalent bonds.2. Other agents interfere with DNA and RNA replication and protein synthesis.Physical Methods of Microbial ControlHeat1. Heat is frequently used to eliminate microorganisms.2. Moist heat kills microbes by denaturing enzymes.3. Thermal death point (TDP) is the lowest temperature at which all bacteria in a liquid culture will bekilled in 10 minutes.4. Thermal death time (TDT) is the length of time required to kill all bacteria in a liquid culture at a giventemperature.5. Decimal reduction time (DRT) is the length of time in which 90% of a bacterial population will bekilled at a given temperature.6. Boiling (100o C) kills many vegetative cells and viruses within 10 minutes. At higher altitudes, time ofheating must be increased to achieve 100o C.7. Autoclaving (steam under pressure) is the most effective method of moist heat sterilization. The steammust directly contact the material for it to be sterilized. Steam, at a temperature of 121o C under 15 psi for 15 min is enough to sterilize at sea level. At higher altitudes the pressure must be increased, which concomitantly increases the temperature of the steam (Boyle's law). See Text, Figure 7.28. In HTST pasteurization, a high temperature is used for a short time (72o C for 15 seconds) to destroypathogens without altering the flavor of the food. Ultra-high- temperature (UHT) treatment (140o C for3 sec.) is used to sterilize dairy productsr Additional Readings: "Why such a mystery over a Mycobacterium" ?, 2000. B. Dixon. ASMNews 66 (7): 384-385. Copyrighted by ASM and reproduced with permission of the ASM.9. Methods of dry heat sterilization include direct flaming, incineration, and hot-air sterilization. Dry heatkills by oxidation. Hot-air sterilization means that an object is heated at 170o C for 2 h.10. Different methods that produce the same effect (reduction in microbial growth) are called equivalenttreatments.Filtration (Text, Figure 7.4)1. Filtration is the passage of a liquid or gas through a filter with pores small enough to retain microbesFiltration is normally used to decontaminate liquid substances sensitive to heat treatment (i.e., enzyme solutions).2. Microbes can be removed from air by high-efficiency particulate air filters (pore size = 0.3 µm).3. Membrane filters composed of cellulose esters are commonly used to filter out bacteria, viruses, andeven large proteins (smallest pore size = 0.01 µM, although 0.2 µM will filter out almost all bacteria). Low Temperature1. The effectiveness of low temperatures depends on the particular microorganism and the intensity of theapplication.2. Most microorganisms do not replicate at ordinary refrigerator temperatures (0o-7o C).3. Many microbes survive (but do not grow) at the subzero temperatures used to store foods. Desiccation1. In the absence of water, microorganisms cannot grow but can remain viable.2. Viruses and endospores can resist desiccation.3. Lyophilization (freeze-drying) is often used as a preservative of foods and microorganisms. This is aclassical example of a paradox! How can lyophilization both prevent microbial growth and preserve it? Osmotic Pressure1. Microorganisms in high concentrations of salts and sugars undergo plasmolysis.2. Molds and yeasts are more capable than bacteria of growing in materials with low moisture or highosmotic pressure (i.e., moldy jam).Radiation1. The effects of radiation depend on its wavelength, intensity, and duration.2. Ionizing radiation (gamma rays, X-rays, and high- energy electron beams, see Text, Fig. 7.5) has a highdegree of penetration and exerts its effect primarily by ionizing water and forming highly reactivehydroxyl radicals3. Ultraviolet (UV) radiation, a form of nonionizing radiation, has a low degree of penetration and causescell damage by making thymine dimers in DNA that interfere with DNA replication; the most effective germicidal wavelength is 260 nm.4. Longer wavelengths of electromagnetic energy, such as microwaves, are not very effective in killingmicrobes. However, microwaves can kill microbes indirectly as materials get hot.Summary of Physical Methods of Control1. For a summary of the physical methods of microbial control and their modes of action, see Text,Table7.5.Chemical Methods of Microbial Control1. Chemical agents may be used on living tissue (as antiseptics) or on inanimate objects (as disinfectants).2. Few chemical agents achieve sterility.Principles of Effective Disinfection1. Careful attention should be paid to the properties and concentration of the disinfectant to be used.2. The presence of organic matter, degree of contact with microorganisms, and temperature should also beconsidered.Evaluating a Disinfectant1. In the use-dilution test, bacterial (S. choleraesuis, S. aureus, and P. aeruginosa) survival in a selecteddilution of a disinfectant is determined.2. Viruses, endospore-forming bacteria, mycobacteria, and fungi can also be used in the use-dilution test.3. In the filter paper method, a disk of filter paper is soaked with a chemical and placed on an inoculatedagar plate; a clear zone of inhibition indicates effectiveness. You cannot determine MICs with thismethod.Types of DisinfectantsPhenol and Phenolics1. Phenolics exert their action by injuring plasma membranes, inactivating enzymes, and denaturingproteins.2. Common phenolics are cresols.Bisphenols1. Bisphenols such as triclosan (over the counter) and hexachlorophene (prescription) are widely used inhousehold products.Biguanides1. Chlorhexidine damages the plasma membrane of vegetative cells.Halogens1. Some halogens (iodine and chlorine) are used alone or as components of inorganic or organic solutions.2. Iodine inactivate enzymes and other cellular proteins by combining with the amino acid tyrosinecausing it to lose its function.3. Iodine is available as a tincture (in solution with alcohol) or as an iodophor (combined with an organicmolecule).4. The germicidal action of chlorine is based on the formation of hypochlorous acid when chlorine isadded to water.5. Chlorine is used as a disinfectant in gaseous form (Cl2) or in the form of a compound, such as calciumhypochlorite, sodium hypochlorite, or chloramines.Alcohols1. Alcohols exert their action by denaturing proteins and dissolving lipids.2. In tinctures, they enhance the effectiveness of other antimicrobial chemicals.3. Aqueous ethanol (60-90%) and isopropanol are used as disinfectants.Heavy Metals and Their Compounds1. Silver, mercury, copper, and zinc are used as germicides.2. They exert their antimicrobial action through oligodynamic action. When heavy metal ions combinewith sulfhydryl (-SH) groups, proteins are denatured.Surface-Active Agents1. Surface-active agents decrease the tension between molecules that lie on the surface of a liquid; soapsand detergents are examples.2. Soaps have limited germicidal action but assist in the removal of microorganisms through scrubbing.3. Acid-anionic detergents are used to clean dairy instrumentation.4. Does bacterial resistance to antibacterial cleaning and hygiene products arise during routine householduse?r Additional Readings:"Antibacterial Cleaning Products and Drug Resistance", Allison E.Aiello, Bonnie Marshall, Stuart B. Levy, Phyllis Della-Latta, Susan X. Lin, and Elaine Larson.2005. Emerging Infectious Diseases. 11 (10): 1565-1570. Copyrighted by CDC and reproducedwith permission from CDC.Quaternary Ammonium Compounds (Quats)1. Quats are cationic detergents attached to NH4+.2. They are also surface-active agents.3. By disrupting plasma membranes, they allow cytoplasmic constituents to leak out of the cell.4. Quats are most effective against gram-positive bacteria.Chemical Food Preservatives1. Sulfur dioxide, sorbic acid, benzoic acid, and propionic acid inhibit fungal metabolism and are used asfood preservatives.2. Nitrate and nitrite salts prevent germination of Clostridium botulinum endospores in meats.3. However, nitrates may cause cancer.Antibiotics1. Nisin and natamycin are antibiotics used to preserve foods, especially cheese.Aldehydes1. Aldehydes, such as formaldehyde and glutaraldehyde, exert their antimicrobial effect by inactivatingproteins.2. They are among the most effective chemical disinfectants.Gaseous Chemosterilizers1. Ethylene oxide is the gas most frequently used for sterilization.2. It penetrates most materials and kills all microorganisms by protein denaturation.Peroxygens (Oxidizing Agents)1. Ozone, peroxide, and peracetic acid are used as antimicrobial agents.2. They exert their effect by oxidizing molecules inside cells.Microbial Characteristics and Microbial Control1. Gram-negative bacteria are generally more resistant than gram-positive bacteria to disinfectants andantiseptics.2. Endospores, protozoan cysts and oocysts, and mycobacteria are very resistant to disinfectants andantiseptics.3. Nonenveloped viruses are generally more resistant than enveloped viruses to disinfectants andantiseptics.4. Prions are resistant to disinfection and autoclaving.Summary1. For a summary of the chemical methods of microbial control and their modes action, see Text,Table 7.82. Summary of efficacy, see Text, Table 7.7.Additional Readings Appendix1. "Why such a mystery over a Mycobacterium?", 2000. B. Dixon. ASM News 66 (7): 384-385.Copyrighted by ASM and reproduced with permission of the ASM.2. "Antibacterial Cleaning Products and Drug Resistance", Allison E. Aiello, Bonnie Marshall, Stuart B.Levy, Phyllis Della-Latta, Susan X. Lin, and Elaine Larson. 2005. Emerging Infectious Diseases. 11(10): 1565-1570. Copyrighted by CDC and reproduced with permission from CDC.。
低温贮藏的定义
低温贮藏的定义低温贮藏是一种有效的食品安全保障技术，总的来说就是将食品保存在较低的温度条件下，以达到食品的安全保质，使食品的质量和营养价值更佳的目的。
主要应用于肉制品、水果蔬菜海产品、奶制品等食品。
低温贮藏的目的，一是降低灭菌时需要的温度，来保护活体的营养物质，达到营养成分保持和色泽华丽，使食品保持最佳质量；二是降低微生物繁殖的环境，从而有效地减少微生物破坏，避免腐败和失水。
从功能上来说，低温贮藏主要有以下四大作用：一是抑制食品中微生物的繁殖。
由于微生物的活动受温度条件限制，减少温度会抑制微生物的繁殖，延缓剩余期。
二是保存食材本身的原味。
低温贮藏可以有效防止风味物质的结合，从而达到保持食材的原始鲜美口感的目的。
三是以少量冰醋酸钠调节食品质量。
由于醋酸钠蒸发温度低，可以将温度控制在一定范围内，避免食材变形，从而促进食品质量的稳定。
四是保持食品的理化性质和营养成分。
由于低温贮藏抑制了蛋白质的水解，可以有效保留食品的营养成分和内在的性质，使食品保持相对稳定。
低温贮藏技术的应用受到广泛的重视，它可以有效的抗击食品安全问题，保障我们的食品安全，为食品提供更好的保质、控制腐败以及阻止微生物增殖，降低食品的制作和流通成本，保持食品更长的期限，使产品能够更有效地流通，受到消费者广泛欢迎。
总之，低温贮藏可以有效地增加食品的保存时间，保护食品的本质属性，确保食物安全。
它在食品安全领域发挥着重要的作用，但也存在一定的风险，所以应该加强相关法规的制定和执行，优化低温贮藏设备的使用，以提高我国的食品安全水平。
Low temperature storage is an effective food safety assurance technology, generally speaking, it is to preserve food under lower temperature conditions to achieve foodsafety and quality and nutritional value of the best purpose. Mainly applied to meat products, fruits and vegetables,aquatic products, dairy products and other foods.The purpose of low-temperature storage is firstly toreduce the temperature required for sterilization to protect the nutrients of the living body, achieve nutrient retention and gorgeous color, so as to maintain the best quality of food, and secondly to reduce the microorganism's breeding environment, so as to effectively reduce microorganism's destruction, avoid corruption and dehydration.Functionally, low-temperature storage mainly has the following four functions:First, inhibit the proliferation of microorganisms in food. Because the activity of microorganisms is restricted by temperature conditions, reducing temperature will inhibit the proliferation of microorganisms and prolong the shelf life.Secondly, preserve the original flavor of food ingredients. Low-temperature storage can effectively prevent the combination of flavor substances, thus achieving the purposeof maintaining the original freshness of food ingredients.Thirdly, adjusting the quality of food with a small amount of sodium acetate. Due to the low evaporation temperature of sodium acetate, the temperature can be controlled within acertain range, so as to prevent the food from deformation, which can promote the stability of food quality.Fourthly, maintain the physical and chemical properties and nutritional components of food. Due to the low temperature storage can inhibit the hydrolysis of protein, so as to effectively retain the nutritional components and inherent properties of food, so that food can maintain relatively stable.The application of low-temperature storage technology has been widely valued, it can effectively combat food safety problems, ensure our food safety, provide better quality control and control of corruption and prevention of microbial growth, reduce food production and circulation costs, retain food for longer periods of time, make products circulate more efficiently and be welcomed by consumers.In conclusion, low-temperature storage can effectively increase the storage time of food, protect the essential properties of food, and ensure food safety. It plays an important role in food safety, but there are also certain risks, therefore, we should strengthen the formulation and enforcement of relevant laws and regulations, optimize the use of low-temperature storage equipment, so as to improve the food safety level of our country.。
6 微生物的生长及其控制(英文教案简版)
over the depression creating a precise volume
between 0.02-0.1uL.
血球计数板
• 1个大方格分为25个中方格，每个中方格分为16个小方格
• 1个大方格分为16个中方格，每个中方格分为25个小方格
• 计数室容积 = 1×1×0.1mm3
• 1mL菌液中的总菌数 =
• No growth occurs;
• Cells are very active metabolically;
• Cells changes very little; • Microbes are sensitive to adverse conditions antibiotics anti-microbial agents
• The length of this time depends on the history of the culture and growth conditions.
If this comes from a fresh culture in the same medium, the lag phase will be short; If the inoculum is old or the medium has been changed ( especially moving bacteria from a rich medium to a poor one )，the lag phase will be longer.
2、Incubation
• A temperature—controlled chamber or incubator; • Setting the optimum temperature and gas content; • Incubation produces a culture---the visible growth of the microbe in the medium.
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a: mesophilic b: thermophilic
Figure: 20-02 The relationship between the temperature and the rate of killing as indicated by the decimal reduction time for two different microorganisms. For organism (a), a typical mesophile, exposure to 110 oC for less than 20 s resulted in a decimal reduction, while for organism (b), a thermophile, 10 min were required to achieve a decimal reduction.
1
Why do we need growth control?
Growth of bacteria can be very fast
One cell can become 4000 times weight of the earth, if exponentially grew for 48 hr
Version-2006
15
Version-2006
16
Figure: 20-03b Use of the autoclave for sterilization. (b) A typical autoclave cycle. Shown is the sterilization of a fairly bulky object. The temperature of the objectVersion-2006 slowly than the rises more temperature of the autoclave.
Version-2006 8
How sensitive is an organism to heating?
D-decimal reduction time
The time required for a ten fold reduction in the population density at a given temperature Relationship of D and temperaturesexponential Slope-a measure of the sensitivity to heat
Consequences of growth of unwanted bacteria
Outside our body-Food spoilage-growth of bacteria in our food, e.g. milk, would deplete nutrition before we can consume it Inside out body-Infectious disease-growth of bacteria within our body would cause health problems
17
Pasteurization
Named for the great microbiologist-Louise Pasteur Killing of non-spore forming bacteria in heat sensitive materials
Removal of pathogens Removal of food spoilage bacteria Keeping quality of the materials
Cells lose their structural integrity-irreversible
Bactericidal-agents that destroy or kill bacteria Bacteriostatic-agents that inhibit bacterial growth
Milk pasteurization
Flash pasteurization-71oC, 15 sec Bulk pasteurization-63-66oC, min
Cardinal temperatures for growth High temperatures over optimum for growth control
Denaturation at high temperature-the lose of structure and ability to function of macromolecules Proteins are the most heat sensitive among the four kinds of macromolecules Higher order structures will be effected first
-accumulation of Ca2+ , small acid-soluble spore proteins (SASPs) and synthesis of dipicolinic acid
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Factors affecting efficiency of heat sterilization
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Growth control measures
Decontamination Treatment that renders an object or inanimate surface safe to handle Disinfection The process of eliminating nearly all pathogens, but not all microorganisms, from inanimate objects or surface Sterilization The killing or removal of all living organisms and their viruses from a growth medium Reduce microbial load The number of viable microorganisms present
The higher the temperature, the quicker the killing The rate of death is proportional at any time to the concentration of organisms at that time (fig 20.1) The time taken for a definite fraction of the cells to be killed is independent of the initial concentration It is necessary to adjust the time and temperature to achieve sterilization
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Spore and Heat Sterilization
Killing of bacterial endospores requires temperature higher than 100 oC Water content determines heat resistant Formation of a gel-like structure
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I Physical Antimicrobial Control
Physical methods
Heat sterilization Radiation sterilization Filter sterilization
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5Hale Waihona Puke Heat Sterilization
Chapter 20 Microbial Growth Control
I Physical Antimicrobial Control II Chemical Antimicrobial Control III Antimicrobial Agents Used In Vivo
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Figure: 20-01 The effect of temperature on the viability of a mesophilic bacterium. The decimal reduction time, D, was obtained for the same mesophilic organism at three different temperatures. D is the time at which only 10% of the original population of organisms remain viable at a given temperature. For 70 oC, D = 3 min; Version-2006 11 for 60 oC, D = 12 min; for 50 oC, D = 42 min.