微生物学：Chapter7控制

1、Chapter VII Control of Microorganisms by Physical and Chemical Agents,Sterilization, Definition of Frequently Used Terms,(Latin sterilis, unable to produce offspring or barren) is the process by which all viable organisms are either destroyed or removed from an object or habitant.,A sterile object i

2、s totally free of viable microorganisms, spores, and other infectious agents.,When sterilization is achieved by a chemical agent, the chemical is called a sterilant.,2. Disinfection,is the killing, inhibition, or removal of microorganisms that may cause disease.,The primary goal is to destroy potent

3、ial pathogens, but disinfection also substantially reduce the total microbial population.,Disinfectant are agents, usually chemical, used to carry out disinfection and are normally used only on inanimate objects. A disinfectant does not necessarily sterilize an object because viable spores and a few

4、 microorganisms may remain.,3. Sanitization,is closely related to disinfection. In sanitization, the microbial population is reduced to levels that are considered safe by public health standards. The inanimate objects is usually cleaned as well as partially disinfected. For example, sanitizers are u

5、sed to clean eating utensil in restaurants.,4. Antisepsis,(Greek anti, against, and sepsis, putrefaction) is the prevention of infection of sepsis and is accomplish-ed with antiseptics. These are chemical agents applied to living tissue to prevent infection by killing or inhibiting pathogen growth.

6、Because they must not destroy too much host tissue, antiseptics are generally not as toxic as disinfectants.,5. Categories of antimicrobial agents,A suffix can be employed to denote the type of antimicrobial agents. Substances that kill organisms often have the suffix cide Latin cida, to kill .,Othe

7、r chemicals do not kill, but they do prevent growth. If these agents are removed, growth will resume. Their names end in static Greek statikos, causing to stand or stopping, for example, bacteriostatic and funhistatic.,A germicide kills pathogens (and many non-pathogens) but not necessarily endospor

8、es. A disinfectant or antiseptic can be particularly effective against a specific group, in which case it may be called a bactericide, fungicide, algicide, or viricide., The Pattern of Microbial Death,1. Microorganisms are not killed instantly when exposed to a lethal agent; rather, the population d

9、ecreases by a constant fraction at constant intervals (exponential killing).,2. A microorganisms is usually considered dead when it is unable to grow in conditions that would normally support its growth and reproduction., Conditions Influencing the Effectiveness of Antimicrobial Agents Activity,1. P

10、opulation size larger populations take longer to kill than smaller populations.,2. Population composition,3. Concentration or intensity of an antimicrobial agent,4. Duration of exposure,5. Temperature,6. Local environment, The Use of Physical Method in Control,1. Heat,Approximate Conditions for Mois

11、t Heat Killing,a. Thermal death point (TDP) is the lowest temperature at which a microbial suspension is killed in 10 minutes.,b. Thermal death time (TDT) is the shortest time necessary to kill all microorganisms in a suspension at a specific temperature and under defined condition.,A. Measuring hea

12、t killing efficiency,c. Decimal reduction time (D, or D value) is the time required to kill 90% of the microorganisms or spores in a sample at a specific temperature.,D value is usually written with a subscript, indicating the temperature for which it applies. D values are used to estimate the relat

13、ive resistance of a microorganism to different temperatures through calculation of the Z value.,d. Z value is the increase in temperature required to reduce D to 1/10 of its previous value.,e. F value is the time in minutes at a specific temperature ( usually 250 0F or 121.1) necessary to kill a pop

14、ulation of cells or spores.,B. Killing with moist heat,a. Boiling water is effective against vegetative cells and eucaryotic spores.,b. Autoclaving (steam under pressure) is effective against vegetative cells and most bacterial endospores.,c. Pasteurization, a process involving brief exposure to tem

15、peratures below the boiling point of water, reduce the total microbial population and thereby increases the shelf life of the treated material; it is often used for heat-sensitive materials that cannot withstand prolong exposure to high temperatures.,i. Low-temperature long-term (LTLT) pasteurizatio

16、n 63 for 30 min.,ii. High-temperature short-term (HTST) flash pasteurization 72 for 15sec.,iii. Ultrahigh temperature (UHT) pasteurization 140 150 for 1to 3 sec.,C. Dry heat can be used to sterilize moisture-sensitive materials such as powders, oils, and similar items; it is less efficient than mois

17、t heat because it usually requires higher temperatures (160 to 170) and longer exposure times (2 to 3 hours).,2. Low Temperature,A. Freezing items an 20 or lower stops microbial growth because of the low temperature and the absent of liquid water. Some ,microorganisms will be killed by ice crystal d

18、isruption of the cell membrane.,B. Freeze is a very good method for long-term storage of microbial samples when carried out properly, and many laboratories have a low-temperature freezer for culture storage at 30 or -70.,C. Refrigeration greatly slows microbial growth and reproduction, but not halt

19、it completely. Fortunately most pathogens are mesophilic and do not grow well at temperature around 4.,3. Filtration,Filtration is an excellent way to reduce the microbial population in solutions of heat-sensitive material, and sometimes it can be used to sterilize solutions. Rather than directly de

20、stroying contaminating microorganisms, the filter simply removes them.,A. Depth filters consist of fibrous or granular materials that have been bonded into a thick layer filled with twisting channels of small diameter. The solution containing microorganisms is sucked through this layer under vacuum,

21、 and microbial cells are removed by physical screening or entrapment and also by absorption to the surface of the filter material.,B. Membrane filters are thin filters with defined pore size that remove microorganisms, primarily by physical screening.,These filters are used to sterilize pharmaceutic

22、als, ophthalmic solutions, culture media, oils, antibiotics, and other heat-sensitive solution.,C. High-efficiency particulate air (HEPA) filters are used in laminer flow biological safety cabinets to sterilize the air circulating in the enclosure.,4. Radiation,A. Ultraviolet (UV) radiation is effec

23、tive but its use is limited to surface sterilization because UV radiation does not penetrate glass, dirt film, water, and other substance.,B. Ionizing radiation (X rays, gamma rays, etc.),1. The characteristics of a desirable disinfectant,A. Ideally the disinfectant must be effective against a wild

24、variety of infectious agents at high dilutions and in the presence of organic matter.,B. Although the chemical must be toxic for infectious agents, it should not be toxic to people or corrosive for common materials.,C. The disinfectant should be stable upon storage, odorless or with a pleasant odor,

25、 soluble in water and lipids for penetration into microorganisms and have a low surface tension so that it can enters cracks in surfaces.,D. If possible the disinfectant should be relatively inexpensive.,2. Commonly used disinfectants and antiseptics,A. Phenolics,Phenol was the first widely used ant

26、iseptic and disinfectant. In 1867 Joseph Lister employed it to reduce the risk of infection during operation. Today phenol and phenolics ( phenol derivatives) such as cresols, xylenols are used as disinfectants in laboratories and hospital. The commercial disinfectant Lysol is made of a mixture of p

27、henolics.,a. Antimicrobial mechanism of phenolics:,Phenolics act by denaturing proteins and disrupting cell membrane.,b. Advantages:,Phenolics are tuberculocidal, effective in the presence of organic material, and remain active on surfaces long after application.,c. Disadvantages:,Phenolics do have

28、a disagreeable odor and can cause skin irritation.,d. Hexachlorophene has been one of most popular antispetic because it persists on the skin once applied and reduces skin bacteria for long periods. However, it can cause brain damage and is now used in hospital nurseries only in response to a staphy

29、lococcal outbreak.,B. Alcohols,a. Alcohol are among the most widely used disinfectans and antiseptics. They are bactericidal and fungicidal but not sporicidal; Some lipid-containing viruses are also destroyed.,b. The two most popular alcohol germicides are ethanol and isopropanol, usually used in ab

30、out 70 to 80% concentration.,c. They act by denaturing proteins and possibly by dissolving membrane lipid.,C. Halogens,A halogen is any of the five elements (fluorine, chlorine, bromine, iodine, and astatine). The exit as diatomic molecules in the free state and form salt-like compounds with sodium

31、and most other metals.,a. The halogens iodine and chlorine are important antimicrobial agents.,b. Iodine is use as a skin antiseptic and kills by oxidizing cell constituents and iodinating cell protein. At high concentration, it may even kill some spores.,i. Iodine often has been applied as tincture

32、 of iodine, 2% or more iodine in a water-ethanol solution of potassium iodide.,ii. Although it is an effective antiseptic, the skin may be damaged, a stain is left, and iodine allergies can result.,iii. More recently iodine has been complexed with an organic carrier to form an iodophor. Iodophor (su

33、ch as Wescodyne, Betadine etc.) are water soluble, stable, and nonstaining, and release iodine slowly to minimize skin burns and irritation.,c. Chlorine is the usual disinfectant for municipal water supplies and swimming pools and is also employed in the dairy and food industries. It may be applied

34、as chlorine gas, sodium hypochlorite or calcium hypochlorite, all of which yield hypochlorous acid (HClO) and then atomic oxygen. The result is oxidation of cellar material and destruction of vegetative bacteria and fungi, although not spores., The Use of Chemical Agents in Control,D. Heavy Metals,E

35、ffective but usually toxic; act by combining with protein, often with their sulfhydryl groups, and inactivate them; also by precipitate cell proteins.,E. Quaternary Ammonium Compounds,Cationic detergents used as disinfectants for food utensils and small instruments, and because of low toxicity, as a

36、ntiseptics for skin; act by disrupting biological membranes and possibly by denaturing proteins.,F. Aldehydes,Both of the commonly used aldehydes, formaldehyde and glutaraldehyde, are highly reactive molecules that combine with nucleic acids and proteins and inactivate them, probably by cross-linkin

37、g and alkylatong molecules. They are sporicidal and can be used as chemical sterilants.,G. Sterilizing Gases,Srerilizing gases (e.g. ethylene oxide, betapropiolactone ) can be used to sterilize heat-sensitive materials such as plastic petri dishes and disposable syringes; act by combing with protein

38、 and inactivating them; recently, vapor-phase hydrogen peroxide has been used to decontaminate biological safety cabinets., Evaluation of Antimicrobial Agent Effectiveness,1. Phenol coefficient test is the best-known disinfectant screening test in which the potency of a disinfectant is compared with

39、 that of phenol., Evaluation of Antimicrobial Agent Effectiveness, Evaluation of Antimicrobial Agent Effectiveness, Evaluation of Antimicrobial Agent Effectiveness,2. A more realistic test is the use of a dilution test; in this test, stainless steel cylinder are contaminated with specific bacterial

40、species under carefully controlled conditions and then exposed to the disinfectant., Chemotherapeutic Agent,Chemotherapeutic agents are chemical agents that are used within the body to treat disease. Chemotherapeutic agents destroy pathogenic microorganisms or inhibit their growth at concentrations

41、low enough to avoid undesirable damage to host., Chemotherapeutic Agent,1. The Development of Chemotherapy,A. Paul Ehrlich (19041909)- aniline dyes and arsenic (arrsphenamine compound #606 in the series. Salvarsan named because it offered salvation from syphilis and contained arsenic. Salvarsan = Sa

42、lvation + arsenic), Chemotherapeutic Agent,B. Gerhard Domagk, and Jacques and Therese Trefouel (19351939) Sulfanilamide (In February 1935, Domagk injected the dye, prontosil, to his daughter Hildegarde, who gravely ill with septicemia. To many historians, her recovery set into age of modern chemothe

43、rapy)., Chemotherapeutic Agent,C. D. D. Woods and E. M. Fildes (1940) Mechanism of action for sulfanilamide.,D. Paul Vuillemin (1889) coined “antibiotic” to describe a substance isolated some years earlier from Pseudomonas aeruginosa. The substance, called pyocyanin, inhibited the growth of other ba

44、cteria in test tubes but was too toxic to be useful in disease therapy., Chemotherapeutic Agent,E. Ernest Duchesne (1896) discovered penicillin; however, this discovery was not followed up and was lost for 50 years.,F. Alexander Fleming (1928) accidently discovered the antimicrobial activity of peni

45、cillin on a contaminated plate; however, follow-up studies convinced him that penicillin would not remain active in the body long enough to be effective., Chemotherapeutic Agent,G. Howard Florey and Ernst Chain (1939) aided by the biochemist, Norman Heatley, worked from Flemings published observatio

46、ns, obtained a culture from him, and demonstrated the effectiveness of penicillin., Chemotherapeutic Agent,H. Selman Waksman (1944)- Streptomycin; this success let to a worldwide search for additional antibiotics, and the field has progressed rapidly since then., Chemotherapeutic Agent,2. General Ch

47、aracteristics of Antimicrobial Drugs,A. Selective toxicity ability to kill or inhibit microbial pathogen with minimal side effects in the host.,a. Therapeutic dose the drug level required for clinical treatment of a particular infection., Chemotherapeutic Agent,b. Toxic dose the drug level at which

48、the agent becomes too toxic for the host (produces undesirable side effects).,c. Therapeutic index the ratio of toxic dose to therapeutic dose: the larger the better., Chemotherapeutic Agent,B. Drugs with narrow-spectrum activity are effective against a limited variety of pathogens; drugs with broad

49、-spectrum activity are effective against a wide variety of pathogens.,C. Chemotherapeutic agents can occur naturally, be synthetic, or semisynthetic (chemical modification of naturally occurring antibiotics)., Chemotherapeutic Agent,D. Drug can be cidal (able to kill) or static (able to reversibly inhibit growth).,E. Minimal inhibitory concentration (MIC) is the lowest concentration of the drug that prevents growth of a pathogen; minimal lethal concentration (MLC) is