Chapter 11物理和化學(xué)因素對(duì)微生物的控制ppt課件

1、Chapter OverviewThe control of microbes in the environment is a constant concern of health care and industry since microbes are the cause of infection and food spoilage(破壞), among other undesirable events.Antimicrobial control is accomplished using both physical technique and chemical agents to dest

2、roy, remove, or reduce microbes in a given area. .Many factors must be contemplated關(guān)注 when choosing an antimicrobial technique, including the material being treated, the type of microbes involved, the microbial load, and the time available for treatment.Antimicrobial agents damage microbes by disrup

3、ting the structure of the cell wall or cell membrane ,preventing synthesis of nucleic acids DNA and RNA, or altering the function of cellular proteins . Microbicidal agents kill microbes by inflicting nonreversible不可逆的 damage to the cell .microbistatic agents temporarily inhibit the reproduction of

4、microbes but do not inflict irreversible damage .Mechanical antimicrobial agents physically remove microbes from materials but do not necessarily kill or inhibit them.Heat is the most physical agent in microbial control and can be delivered in both moist (steam sterilization, pasteurization) and dry

5、 forms.Radiation exposes material to high energy waves that can enter and damage microbes. Examples are ionizing and ultraviolet radiation.Chemical antimicrobial are available for every level of microbial treatment, from low-level disinfectants to high-level sterilants. Antimicrobial chemical includ

6、e halogens, alcohols, phenolics, peroxides, heavy metals, detergents, and aldehydes.Controlling Microorganisms Controlling our degree of exposure to potentially harmful microbes is a monumental非常的 concern in our lives, and it has a long and eventful艱苦的 history.GENERAL CONSIDERATIONS IN MICROBIAL CON

7、TROLThe methods of microbial control belong to the general category of decontamination凈化 procedures, in that they destroy or remove contaminants. Most decontamination methods employ either physical agents, such as heat or radiation, or chemical agents such as disinfectants and antiseptics無(wú)菌的 .RELATI

8、VE RESISTANCE OF MICROBIAL FORMSThe primary targets of microbial control are microorganisms capable of causing infection or spoilage that are constantly present in the external environment and on the human body .This targeted population is rarely simple or uniform; in fact, it often contains mixture

9、s of microbes with extreme difference in resistance and harmfulness. .Contaminants that can have far-reaching effects if not adequately controlled include bacterial vegetative cells and endospores, fungal hyphae and spores, yeasts, protozoan trophozoites滋養(yǎng)體 and cysts, worms, insects and their eggs,

10、and viruses. This scheme compares the general resistance these forms have to physical and chemical methods of control:.Highest resistance Bacterial endosporesModerate resistance Protozoan cysts: some fungal sexual spores (zygospores接合孢子);some viruses. In general, naked viruses are more resistant tha

11、n enveloped forms.Least resistance Most bacterial vegetative cells; fungal spores and hyphae; enveloped viruses; yeasts; and protozoan trophozoites. Actual comparative figures on the requirements for destroying various groups of microorganisms are shown in table 11.1.TERMINOLOGY 術(shù)語(yǔ)AND METHODS OF MIC

12、ROBIAL CONTROLThrough the years, a growing terminology has emerged for describing and defining measures that control microbes. To complicate matters, the everyday use of some of these terms can at times be vague and inexact.SterilizationSterilization is a process that destroys or removes all viable

13、microorganisms, including viruses. Any material that has been subjected to this process is said to be sterile.Sterilized products are essential to human well-being. Although most sterilization is performed with a physical agent such as heat, a few chemical called sterilants can be classified as ster

14、ilizing agents because of their ability to destroy spores.At times, sterilization is neither practicable nor necessary, and only certain groups of microbes need to be controlled. Keep in mind that the destruction of spores is not always a necessity .SterilizationHigh Temperature高溫Ultraviolet Rays紫外線

15、.High temperature can make protein、nucleic acid核酸 、 lipid脂類 and other macromolecules生物大分子 to degraded 降解、denaturalized變性 and destoryed.High Temperature.High Temperature SterilizationDry Heat Sterilization(干熱空氣滅菌法)Moist Heat Sterilization(濕熱空氣滅菌法)Flame Burn灼燒High Temperatue in Oven 干熱空氣滅菌Normal Press

16、ureHighPressure.Pasteurization (巴氏消毒法) Boiling煮沸法Tyndallization(間歇滅菌法)Continuous Pressure Sterilization延續(xù)高壓滅菌Normal PressureHighPressureNormal Pressure Sterilization常壓滅菌.Flame BurnOese(接種環(huán)) .High Temperatue in Oven Oven烘箱Culture Dish(培育皿)Method: 160 C for 2 Hours.Pasteurization (巴氏消毒法)Louis Pasteur

17、(December 27, 1822 September 28, 1895 )Louis Pasteur was a French chemist and microbiologist best known for his remarkable breakthroughs in the causes and prevention of disease. .Conception of Pasteurization The heating of every particle of milk or milk product to a specific temperature for a specif

18、ied特定的 period of time.Aim:Heating liquids for the purpose of destroying bacteria, protozoa原生動(dòng)物 ,molds霉菌, and yeasts酵母. .Pasteurization System 巴氏消毒系統(tǒng)The Structure of Pasteurizer.Pasteurization HIgh Temperature/Short Time(超高溫瞬時(shí)滅菌HTST)Low Temperature Holding Method(低溫維持法LTH)63 C for 30 minutes C for se

19、veral seconds . Boiling煮沸法Method: 100 C for several minutes .Tyndallization間歇滅菌法Conception: Tyndallization is a method used to destroy bacteria and endospores芽孢 which requires no pressure cooker. .1.80-100 Cfor 15-60 Mintues 2.37 C for OvernightInducing Spore(芽孢) GerminationSterilized MediumRepeat t

20、he Cycle Several TimesFlow of Tyndallization .Normal Autoclaving常規(guī)高壓滅菌 Continuous Autoclaving延續(xù)高壓滅菌High PressureAutoclaving(滅菌).An autoclave滅菌器 is a pressureized壓力的 device designed to heat aqueous(含水的 ) solutions溶液 above their boiling point沸點(diǎn) at high atmospheric pressure to achieve sterilization .Au

21、toclave.Old Style AutoclaveModern Autoclave高壓滅菌器.Normal Materials:121 C for 15-20 minutes.Special Materials (For Lactose乳糖):115 C for 35 minutes. Flow of Normal AutoclavingWater is boiling水加熱到沸騰Turn Off the Valve封鎖排氣閥Increasing and Maintaining Pressure in the SpecificTime升壓、定時(shí)保壓Decreasing Pressurean

22、d Discharging Water Vapour降壓并排出蒸汽.If you just turn off the valve before boiling. Result?.Water VapourCool AirWater VapourA：110， 0.12MPaB：121 ， 0.12MPaPressure:There is no difference in pressue between A and B;Temperature:It is obvious that the temperatureOf B is higher than that of A. .Continuous Au

23、toclavingPrinciple:All the medium培育基 are heated 、maintained、cooled fast when they pass through the tubes.Continuous Autoclaving(延續(xù)高壓滅菌器).Microbial AgentsThe root-cide, meaning to kill, can be combined with other terms to define an antimicrobial agent aimed at destroying a certain group of microorgan

24、isms. For example, a bactericide(殺菌劑 ) is a chemical that destroys bacteria except for those in the endospore stage. It may or may not be effective on other microbial groups.Agents That Cause Microbistasis Bacteriostatic agents prevent ,and fungistatic chemical Inhibit fungal growth. Materials used

25、to control microorganisms in the body(antiseptics and drugs)have microbistatic effects because many microbicidal compounds can be too toxic to human cells.Germicides, Disinfection, AntisepsisA germicides, also called a microbicide, is any chemical agent that kills pathogenic microorganisms. A germin

26、cide can be used on inanimate (nonliving) materials or on living tissue, but it ordinarily can not kill resistant microbial cells. Any physical or chemical agent that kills “germs is said to have germicidal properties. The related disintection,*refers to the use of a physical process or a chemical a

27、gent(a disinfectant)to destroy vegetative pathogens but not bacterial endospores.In modern usage, sepsis is defined as the growth of microorganisms in the body or the presence of microbial toxins in blood and other tissues. The term asepsis* refers to any practice that prevents the entry of infectio

28、us agents into sterile tissues and thus prevents infection. Aseptic techniques commonly practiced in health care range from sterile methods that exclude all microbes to antiseptics*. .In antisepsis, chemical agents called antiseptics are applied directly to exposed body surfaces (skin and mucous mem

29、branes) ,wounds, and surgical incisions to destroy or inhibit vegetative pathogens.Methods That Reduce the Numbers of Microorganisms. Several applications in commerce and medicine do not require actual sterilization, disinfection, or antisepsis but are based on reducing the levels of microorganisms(

30、the microbial load)so that the possibility of infection or spoilage is greatly decreased .Restaurants, dairies, breweries, and other food industries consistently handle large numbers of soiled utensils that could readily become sources of infection and spoilage. .These industries must keep microbial

31、 levels to a minimum during preparation and processing. Sanitization * is any cleansing technique that mechanically removes microorganisms as well as other debris to reduce contaminations to safe levels. A sanitizer is a compound such as soap or detergent used to perform this task. Cooking utensils,

32、 dishes, bottles, cans, and used clothing that have been washed and dried may not be completely free of microbes, but they are considered safe for normal use (sanitary).It is often necessary to reduce the numbers of microbes on the human skin through degermation. This process usually involves scrubb

33、ing the skin or immersing it in chemicals, or both. It also emulsifies oils that lie on the outer cutaneous layer and mechanically removes potential pathogens on the outer layers of the skin.WHAT IS MICROBIAL DEATH? Signs of life in complex organisms such as animals are self-evident, and death is ma

34、de clear by loss of nervous function, respiration, or heartbeat. In contrast, death in microscopic organisms that are composed of just one or a few cells is often hard to detect, .because they reveal no conspicuous(顯著的 ) vital signs to begin with. Lethal agents (such as radiation and chemicals) do n

35、ot necessarily alter the overt appearance of microbial cells. Even the loss of movement in a motile microbe cannot be used to indicate death. This fact has made it necessary to develop special qualifications(目的) that define and delineate描畫 microbial death.Factors That Affect Death Rate The ability t

36、o define microbial death has tremendous theoretical and practical importance. It allows medicine and industry to test the conditions required to destroy microorganisms, to pinpoint探明 the ways that antimicrobial agents kill cells, and to establish standards of sterilization and disinfection in these

37、fields. The cells of a culture show marked variation in susceptibility 敏感性to a given microbicidal agent. Death of the whole population is not instantaneous but begins when a certain threshold拐點(diǎn) of microbicidal agent is met and continues in a logarithmic對(duì)數(shù)的 manner as the time or concentration of the

38、agent is increased (figure11.2). The effectiveness of a particular agent is governed by several factors besides time. These additional factors influence the action of antimicrobial agent 殺菌劑.1. The number of microorganisms (figure11.2b).A higher load of contaminants requires more time to destroy. 2.

39、 The nature of the microorganisms in the population (figure11.2c). In most actual circumstances of disinfection消毒 and sterilization, the target population is not a single species of microbe but a mixture of bacteria, fungi, spores, and viruses, presenting an even greater spectrum of microbial resist

40、ance.3. The temperature and pH of the environment.4. The concentration (dosage, intensity) of the agent. For example, UV radiation is most microbicidal at 260 nm; most disinfectants are more active at higher concentrations.5. The mode of action of the agent (figure11.2d). How does it kill or inhibit

41、 the microorganism?6. The presence of solvents有溶解力的, interfering organic matter, and inhibitors. Large amounts of saliva, blood, and feces can inhibit the actions of disinfectants and heat.HOW ANTIMICROBIAL AGENTS WORK: THEIR MODES OF ACTION An antimicrobial agents adverse不利的 effect on cells is know

42、n as its mode of action. Agents affect one or more cellular targets, inflicting damage progressively until the cell is no longer able to survive. Antimicrobials have a range of cellular targets, with the agents that are least selective in their targeting tending to be effective against the widest ra

43、nge of microbes.The cellular targets of physical and chemical agents fall into four general categories: 1. the cell wall. 2. the cell membrane. 3. cellular synthetic processes (DNA,RNA), and 4. proteins.The Effects of Agents on the Cell Wall The cell wall maintains the structural integrity of bacter

44、ial and fungal cells. Several types of chemical agents damage the cell wall by blocking its synthesis, digesting it, or breaking down its surface. A cell deprived of a functioning cell wall becomes fragile(脆弱的) and is lysed溶解very easily.How Agents Affect the Cell Membrane All microorganisms have a c

45、ell membrane composed of lipids and proteins, and we learned in previous chapter, a cells membrane provides a two-way system of transport. If this membrane is disrupted, a cell loses its selective permeability透過(guò)性 and can neither prevent the loss of vital molecules nor bar the entry of damaging chemi

46、cals.Agents That Affect Protein and Nucleic Acid Synthesis Microbial life depends upon an orderly and continuous supply of proteins to function as enzymes and structural molecules. As we saw in chapter 9, these proteins are synthesized on the ribosomes through a complex process called translation. F

47、or example, the antibiotic choramphenicol氯霉素 binds to the ribosomes of bacteria in a way that stops peptide bonds from forming proteins required in growth and metabolism and are thus inhibited from multiplying.The nucleic acids are likewise necessary for the continued functioning of microbes. Some a

48、gents bind irreversibly to DNA, preventing both transcription and translation; others are mutagenic agents. Gamma, ultraviolet, or X radiation causes mutations that result in permanent inactivation of DNA. Chemicals such as formaldehyde甲醛 and ethylene乙烯 oxide also interfere with DNA and RNA function

49、.Practical Concerns in Microbial ControlNumerous considerations govern selection of a workable method of microbial control. These are among the most pressing concerns:.1. Does the application require sterilization, or is disinfection adequate? In other words, must spores be destroyed, or is it neces

50、sary to destroy only vegetative pathogens?.2. Is the item to be reused or permanently discarded? If it will be discarded, then the quickest and least expensive method should be chosen.3. If, it will be reused, can the item withstand heat, pressure, radiation, or chemicals? .4. Is the control method

51、suitable for a given application? (For example, ultraviolet radiation is a good sporicidal殺孢子的 agent, but it will not penetrate solid materials.) Or, in the case of a chemical, will it leave an undesirable residue殘基 ?.5. Will the agent penetrate to the necessary extent?6. Is the method cost-and labo

52、r-efficient, and is it safe?.A remarkable variety of substances can require sterilization. They run the gamut整個(gè)領(lǐng)域 from durable solids such as rubber to sensitive liquids such as serum血清 , and form air to tissue grafts移植.Considerations such as cost, effectiveness, and method of disposal are all impor

53、tant. For example, the disposable plastic items such as catheters導(dǎo)管 and syringes注射器 that are used in invasive侵略性的 medical procedures have the potential for infecting the tissues. These must be sterilized during manufacture by a nonheating method (gas or radiation), because heat can damage delicate p

54、lastics.Methods of Physical ControlMicroorganisms have adapted to the tremendous diversity of habitats the earth provides, even seven conditions of temperature, moisture, pressure, and light. For microbes that normally withstand such extreme physical conditions, our attempts at control would probabl

55、y have little effect. Fortunately for us ,we are most interested in controlling microbes that flourish in the same environment in which humans lives. .The vast majority of these microbes are readily controlled by abrupt changes in their environment. Most prominent among antimicrobial physical agent

56、is heat. Other less widely used agents include radiation ,filtration,ultrasonic waves超聲波,and even cold. The following sections will examine some of these methods and explore their practical applications in medicine,commerce and the home.Practical Concerns in the Use of Heat:Thermal Death Measurement

57、sAdequate sterilization requires that both temperature and length of exposure be considered .As a general rule, higher temperatures allow shorter exposure times, and lower temperatures require longer exposure times. A combination of these two variable constitutes the thermal death time致死時(shí)間, or TDT,d

58、efined as the shortest length of time required to kill all test microbes at a specified temperature. .The TDT has been experimentally determined for the microbial species that are common or important contaminants in various heat-treated materials. Another way to compare the susceptibility of microbe

59、s to heat is the thermal death point致死溫度TDP),defined as the lowest temperature required to kill all microbes in a sample in 10 minutes.THE EFFECTS OF COLD AND DESICCATION The principal benefit of cold treatment is to slow growth of cultures and microbes in food during processing and storage. It must

60、 be emphasized that cold merely retards延遲 the activities of most microbes.Although it is true that some microbes are killed by cold temperatures,most are not adversely affected by gradual cooling, long-term refrigeration, or deep-freezing. In fact, freezing temperatures, ranging from -70 to-, provid