4. Technology

Food Spoilage and Preservation. Consideration of the production and preservation of foods will illustrate the practical application of knowledge of the physiological properties of microorganisms. The type of decomposition that will occur in a food depends on its chemical composition, its environment, and the opportunity for contamination. Aerobically, molds are frequently the major decomposing agent, especially of cheese, the surfaces of meats, and acid fruit and vegetables. Yeasts bring about alcoholic fermentation in fruit juices and other sugar-containing liquids. Bacteria are more often concerned with changes in foods high in protein and starch, especially under anaerobic conditions and if the foods are neutral.

4、技术

    食品变质与保存。对食物生产和保存的考虑将说明有关微生物生理特性知识的实际应用。食物中出现的腐烂类型取决于其化学成分、环境和受污染的机会。在有氧的情况下，霉菌通常是主要的腐烂剂，尤其是奶酪、肉类的表面以及酸性水果和蔬菜。在果汁和其它含糠的液体中，酵母菌会引起酒精发酵。人们更关心的是细菌在高蛋白和高淀粉食品中的变化，尤其是在厌氧的条件下，以及食品是中性的情况下。

The THREE basic principles of food preservation are exclusion of microorganisms, inhibition of their growth, and their destruction. Examples of the first principle are to be seen in the natural protection afforded by the skin of fruits and the shells of eggs. Ordinarily, since it is not feasible to produce food under completely sterile conditions, this principle is used chiefly to keep down the “initial load.” In the meat industry and in the production of milk for direct consumption or for conversion into dairy products, sanitation measures for reducing the initial load provide the key to successful preservation.

食品保存的三个基本原则是排除微生物，抑制它们的生长和灭菌。第一个原则的例子可从果皮和蛋壳提供的自然保护中看到。通常，由于在完全无菌的条件下生产食品是不可行的，因此这一原则主要是控制“最初负载”。在肉类加工业和直接消费或转变成乳制品的牛奶生产中，降低最初负载的卫生措施为成功保存提供了关键措施。

The second principle of inhibition of bacterial growth requires that the initial load be kept under population control. Effective physical methods include lowering the temperature, exemplified by chilling milk and the carcasses of butchered animals, and drying, as in the dehydration of fruits and vegetables. Such chemical agents as sugar and salt preserve by raising the osmotic pressure; at times, however, osmophiles will develop in brines, heavy sugar syrups, and honey. Other useful chemicals are organic acids, especially acetic acid in the form of vinegar, for pickling, and lactic acid, produced naturally in green plant tissue by members of the Lactobacillaceae to form sauerkraut, silage, and fermented pickles and olives. The addition of other preservative chemicals such as benzoate to soft drinks, propionate to control mold on bread, sulfite to dried fruits, and antibiotics to fish and poultry is regulated by law. See also FOOD—4. Food Additives.

抑制细菌生长的第二个原则需要将最初负载保持在种群控制之下。有效的物理方法包括降低温度，例如冷却牛奶和屠宰的动物尸体和风干，如同水果和蔬菜的脱水。像糖和盐这样的化学制剂通过提高渗透压可保存食物；然而，有时嗜高渗菌会在盐水、高糖糖浆以及蜂蜜中生长。其它有用的化学物质是有机酸，尤其是以醋的形式形成的醋酸，用于泡菜，而在绿色植物组织中由乳酸菌科成员自然产生的乳酸制成了德国泡菜、青贮饲料以及发酵泡菜和橄榄。法律规定了其它防腐化学物质的添加物，如用于软饮料中的苯酸盐，控制面包霉菌的丙酸盐，用于干果的亚硫酸盐，以及鱼和家禽使用的抗生素。也可参阅食品—4、食品添加剂词条。

An example of the THIRD principle, destruction of bacteria, is the destruction of microorganisms by heat in pasteurization of milk and beverages and in the canning of foods. The technical problem is that of destroying all organisms that might cause trouble without lowering the quality of the product through excessive heating. In milk this is accomplished by exposing it to a temperature of 62.8゜C for 30 minutes or to 71.6゜for 15 seconds. Pathogens are eliminated by this method, and the population of lactic acid bacteria is so reduced that souring will not occur for several days under proper refrigeration. In canning, heat treatment seeks to destroy even the spore formers, since many of these will develop under anaerobic conditions at room temperature. At times some spore formers, notably spore-forming thermophiles, will survive the processing and may cause such defects as flat souring through the formation of lactic acid by Bacillus stearothermophilus; so-called TA spoilage by acid and gas evolved by thermophilic anaerobic spore formers; and “stinker,” hydrogen sulfide originating from Clostridium nigrificans. Finally, ultraviolet radiation is used to kill molds on the surfaces of meat, cheese, and bread. See also CHEESE AND CHEESE MAKING—Pasteurization.

第三个原则灭菌的一个例子是在牛奶和饮料和罐装食品产生中用巴氏杀菌法加热杀灭微生物。技术问题是，在不用过度加热，不降低产品质量的情况下杀灭可能引起麻烦的所有有机体。在牛奶的杀菌中，将其置于摄氏62.8度的温度中30分钟，或摄氏71.6度的温度中15秒来完成。用这种方法可消灭病原体，而且这样也可减少乳酸菌的种群，以至于在适当的冷藏条件下好几天都不会出现变酸的情况。在罐装中，加热处理甚至会消灭产孢菌类，因为许多细菌会在室温的厌氧条件下生长。有时一些产孢菌类，特别是孢子形成的嗜热菌，会在该过程中存活下来，并且通过由嗜热脂肪芽孢杆菌形成乳酸，可能导致出现平酸这样的问题；所谓的由酸和由嗜热厌氧产孢菌类形成的气体导致的TA变质；而“臭味”，是源自黑梭状芽孢杆菌的硫化氢。最后，可使用紫外线辐射杀灭肉、奶酪和面包表面的霉菌。也可参阅奶酪与奶酪制作—巴氏灭菌法词条。

Food Manufacture.  Probably the most important food products dependent on microbial activity are the various types of cheese. Species of the Lactobacillaceae form lactic acid from the lactose of milk which, together with the added enzyme rennin, produces a curd of the casein (a milk protein). Much of the soluble material is then expressed as whey, a watery substance. After salting, the curd can be consumed directly (for example, as cottage cheese), but most cheeses require a period of curing or ripening during which the casein breaks down. The extent of this will depend on environmental factors that favor the development of certain types of curing agent present in the milk or added as a “starter.” These factors include temperature used in manufacture and during curing; humidity; size of cheese; time; and amount of salt. Lactobacilli are largely responsible for ripening Cheddar cheese, but the Swiss type requires in addition an “eye former,” which is a species of Propionibacterium. Brick and Limburger cheeses are cured by a mixture of proteolytic, aerobic, and facultative organisms growing as a “smear” on the surface. The mold, Penicillium camemberti, also is a P. roquefortic, although aerobic, can grow through Roquefort, since holes are punched in the young cheese to let in air. See also CHEESE AND CHEESE MAKING.

食品加工。很可能，取决于微生物活性最重要的食物产品是各种类型的奶酪。乳酸菌科的种类从牛奶的乳糖中形成乳酸，连同添加的凝乳酶的酶，产生一种酪蛋白的凝乳（一种牛奶蛋白质）。然后，许多水溶性物质呈现出乳清，一种水的物质。盐渍后，凝乳可直接食用（例如，白软干酪），但大多数奶酪都需要一段时期固化或成熟，此期间酪蛋白会分解。这种程度将取决于环境因素，这有利于牛奶或加入的“起始物”中存在的某些类型固化剂的发展。这些因素包括生产中使用的温度和固化时间；湿度；奶酪的大小；时间；以及盐的用量。乳酸杆菌是切达干酪熟化的主要原因，但瑞士的乳酸杆菌类型需要另外的“眼孔成型者”，它是一种丙酸菌属。布里克和林堡干酪是由一种蛋白水解的、好氧的和兼性的有机体混合物，在表面形成的一种“污渍”。这种霉菌，沙门柏干酪青霉也是一种洛克福羊乳干酪青菌，但由于在未熟化的奶酪中打了孔，使得空气进入其中，尽管好氧，但可通过洛克福羊乳干酪生长。也可参阅奶酪和奶酪制作词条。

Cultured buttermilk owes its distinctive flavor and aroma to bacteria. In its preparation, pasteurized skimmed milk is inoculated with acid-forming bacteria, which ferment lactose to lactic acid, and with aroma formers, which ferment citric acid to diacetyl and other aromatic compounds. Sometimes these bacteria are grown in cream before it is churned into butter.

人工培育的酪乳的独特风味和芳香要归功于细菌。在其备制过程中，巴氏消毒的脱脂奶接种了酸形成的细菌，它将乳糖发酵成乳酸，并加入芳香剂，将柠檬酸发酵成二乙酰和其它的芳香化合物。有时，这些细菌在搅拌成黄油前生长在奶油中。

Chemical Manufacture.  One of the earliest uses of bacteria for a commercial process was the water-retting of flax (for linen) and hemp (for rope) by pectin-destroying clostridia such as Clostridium felsineum and C. pectinovorum. Today the important industry employing bacterial fermentation is devoted to the production of antibiotics, mostly by species of the higher bacteria belonging to the order Actinomycetales, especially those in the Streptomycetaceae family. (See ANTIBIOTIC; PENICILLIN; PLANTS AND PLANT SCIENCE—14. Modern Medicinal Plants.) A vitamin B12 preparation used in feeds is a by-product of the production of streptomycin, but it is also made commercially by a strain of Propionibacterium freudenreichii. Industrial lactic acid is made by the Lactobacillus delbrueckii.

化学制品的生产。最早将细菌用于商业过程的方法之一是通过破坏果胶的梭状芽胞杆菌，用水浸法对亚麻（亚麻布）和麻类植物（麻绳）进行处理，诸如毡毛梭菌和果胶梭菌。今天，利用细菌发酵的重要行业致力于抗生素的生产，主要是属于放线菌目高等细菌属，尤其是那些链霉菌家族的种类。（参阅抗生素；青霉素；植物与植物学—14. 现代药用植物词条）。在饲料中使用的维生素B12制剂就是链霉素生产的副产品，但在商业上，它也是由一种费氏丙酸杆菌属制成的。工业乳酸是用德氏乳酸杆菌制成的。

Often overlooked among the commercial products formed by microorganisms are the enzyme preparations. Alpha-amylase from selected strains of Bacillus subtilis is used to hydrolyze starch to dextrin in making certain types of beer, in clarifying beer, and in desizing textiles. Also, B. Subtilis forms a proteinase that is useful for desizing silk, removing protein from hides in tanning, and reducing protein haze in beer. These two bacterial enzymes are especially useful, since they have a tolerance to heat higher than those from other sources.

在由微生物形成的商业产品中常常被忽视的是酶制剂。从选定的枯草杆菌菌株中提取的阿尔法-淀粉酶在酿造某些种类的啤酒，在澄清啤酒，以及在纺织品退浆时被用来将淀粉水解成糊精。此外，枯草杆菌形成了一种蛋白酶，对丝绸退浆，祛除鞣革中的蛋白质，以及降低啤酒中的蛋白质浑浊很有用。这两种细菌酶特别有用，因为它们比那些来自其它来源的细菌酶具有更高的耐热性。

 

5. Ecology

Of greater importance than the technical applications just discussed are the roles played by bacterial in their natural habitats: soil, water, and host plants and animals. In soil and water, bacteria are involved in what is called the cycle of the elements.

5、生态学

比刚才讨论的技术应用更为重要的是细菌在其自然栖息地所起的作用：土壤、水，宿主植物和动物。在土壤和水中，细菌涉及到所谓的元素循环。

The Carbon Cycle.  Green plants take simple compounds such as carbon dioxide, nitrates, and phosphates and build them into complex organic substances: carbohydrates, proteins, and fats. When the plant dies, these are returned to the soil; they can, of course, be consumed by animals and converted into tissue, but eventually most reach the soil or sea in the form of plant and animal remains or as manures and sewage. The organic substances must be mineralized before succeeding crops can reutilize the elements. The necessary decompositions carried out by fungi and bacteria may be either aerobic, in which case the end products are carbon dioxide and water, or anaerobic, in which event such fermentation products as organic acids may accumulate to be destroyed by aerobic microorganisms when oxygen becomes available. Such organic acids may cause a problem by “souring” the soil, but they can also help in solubilizing some soil minerals.

碳循环。绿色植物吸收简单的化合物，如二氧化碳，氮和磷酸盐，并将它们发展成复杂的有机物：糖类、蛋白质和脂肪。当植物死亡时，这些有机物返回到土壤中；当然，它们可被动物消耗并转变成组织，但最终大多会以植物和动物残留物的形式进入土壤或海洋，或作为肥料和污水。有机物质必须先矿化，农作物才能再利用这些元素。由真菌和细菌进行的必要分解既可能是好氧的，在这种情况下最终的产物是二氧化碳和水，也可能是厌氧的，在这种情况下，这种作为有机酸的发酵产物在氧气可用时会累积到被好氧的微生物破坏。这样的有机酸可造成土壤“酸化”的问题，但它们也能帮助溶解某些土壤矿物质。

The Nitrogen Cycle. In the nitrogen cycle, proteins are first broken down to amino acids; the amino group is then liberated by conversion to ammonia. Aerobically, the filamentous fungi, actinomycetes, and species of Bacillus are largely concerned with such “ammonification,” but anaerobically the clostridia and other bacterial species are the effective agents. The ammonia can be used as such by plants, but often it is converted into nitrite by the chemolithotroph Nitrosomonas, and the nitrite into nitrate by Nitrobacter. This completes the cycle, but along the way the nitrate may be used anaerobically by some bacteria as an electron acceptor in place of oxygen, liberating the nitrogen as the molecule to the vast reservoir in the atmosphere.

氮循环。在氮循环中，蛋白质首先分解成氨基酸；然后氨基通过转化成氨而释放。在好氧的情况下，丝状真菌、放线菌以及芽孢杆菌主要与这种“氨化”有关，但在厌氧的情况下，梭状芽胞杆菌和其它的细菌种类是有效的催化剂。氨自身可被植物利用，但它通常被化能无机营养物亚硝化单胞菌转化成亚硝酸盐，并由硝化菌属将亚硝酸盐转化成硝酸盐。这就完成了循环，但随着该进程的发展，硝酸盐可能被一些细菌以厌氧的方式作为电子受体代替氧气，将氮气作为分子释放到大气的巨大储层中。

Eventually, all the nitrogen in the organic world would be unavailable as the inert molecules were it not for the existence of a compensatory process called nitrogen fixation. Hermann Hellriegel and Hermann Wilfarth discovered (1886) the most important type of fixation, which occurs through the association of leguminous plants with species of the root nodule bacterium Rhizobium. The bacterium invades the roots of legumes, causing formation of a nodule in which free nitrogen is converted into amino acids via ammonia. This process, called symbiotic nitrogen fixation, also occurs in several genera of non-legumes (alder and bog myrtle, for instance); although here the associated endophyte (plant within a plant) has not been established, it is not Rhizobium. Asymbiotically, nitrogen is fixed both aerobically and anaerobically by several free-living forms, including species of Azotobacter and Clostridium; Aerobacter aerogenes; Bacillus polymyxa; representatives of all the photosynthetic bacteria; and blue-green algae.

最终，如果不是因为存在一种称为固氮的补偿过程，那么有机世界中的所有氮气都会作为惰性分子而无法使用。赫尔曼·赫尔利格尔和赫尔曼·惠尔法斯发现了（1886年）最重要的固氮类型，它是通过豆科植物与根结细菌属根瘤菌的结合所产生的。该细菌侵入豆类的根部，导致结节的形成，其中，游离氮通过氨转变成氨基酸。这个称为共生固化氮的过程也在一些非豆科植物（例如，桤木和桃金娘）的属中出现；尽管在这里相关的内生菌（一种植物中的植物）尚未建立，但它不是根瘤菌。非共生地，氮通过各自独立生存的形式在好氧和厌氧的的条件下固定，包括固氮菌属和梭状芽孢杆菌；产气杆菌；多粘芽孢杆菌；所有光合细菌的代表；以及蓝绿藻。

It should be noted that no all of the organic matter returned to soil is mineralized immediately; a residue called humus gives soil desirable physical properties and helps to prevent leaching of soluble ions. This organic fraction decomposes slowly, finally releasing its mineral elements to the plant. In addition to participating in the carbon and nitrogen cycles, humus has numerous other functions. (See HUMUS.) The populations of the various species of soil microorganisms vary with the environment, which includes such physiological factors as supply of food, oxygen, and water; temperature; and pH, or alkaline and acid reaction. (See SOIL---Soil Characteristics: Acidity and Salts.) The farmer exerts some control over these factors and hence over the microorganism’s activities through such cultural practices as plowing, draining, irrigating, and liming.

应当注意的是，并不是所有返回到土壤中的有机物都立刻被矿化；一种称为腐殖质的残留物给予土壤合适的物理性质，有助于防止水溶性离子的淋洗。这种有机馏分分解缓慢，最后将其矿物元素释放给植物。除了参与碳循环和氮循环，腐殖质还具有许多其它的功能。（参阅腐殖质词条）。

Sewage Disposal.  Domestic and industrial sewage was once disposed of merely by running the waste into a body of water or onto vacant land. Today large communities seldom have or resort to such facilities. In their place the sanitary engineer has developed large disposal plants for handling an average of 150 gallons per day per inhabitant. In these plants the processes normally occurring in soil are carried out expeditiously in tanks.

污水处理。曾经处理生活与工业污水仅仅是将废物排入水域，或者置于空地上。今天，大型社区很少拥有或依靠这样的设施。在他们生活的地方，卫生工程师已建立平均每人每天150加仑的大型污水处理厂。在这些工厂中，通常在土壤中发生的过程在这些污水容器中也在迅速进行着。

In the Imhoff septic tank, anaerobic fermentations rapidly make soluble some of the organic matter colloidally suspended in the raw sewage flowing through the upper chamber; the remainder-settles into a lower chamber for prolonged decomposition that eventually forms a humus-like material called sludge. The soluble material then is often sprayed onto a trickling filter in which a film of bacteria and protozoa on coarse rocks completes the oxidation.

在伊姆霍夫化粪池中，厌氧发酵迅速使一些胶状的可溶性有机物流经罐的上部，悬浮在未经处理的污水中；剩下的部分进入罐的下部，延长分解时间，最终形成称为污泥的类似腐殖质的物质。然后，可溶性物质通常被喷到一个滴滤器上，在滴滤器中，在粗粒岩石上的一层细菌和原生动物薄膜上完成氧化。

Oxidation by similar groups of microorganisms is the initial step in the activated-sludge process. The raw sewage is inoculated with flocculent masses of microbial cells and protozoa and is vigorously aerated as it flows through tanks. In from five to eight hours most of the readily oxidizable organic matter has been oxidized, and the colloidal particles have flocculated to form more activated sludge. This readily settles out, and about one quarter is used for inoculums; the excess is dried for fertilizer or is further decomposed by slow fermentation in anaerobic gas holders. The gas formed—78 percent methane—can be used in gas engines to run the plant. See also SANITARY ENGINEERING—Sewage Treatment.

通过类似微生物群的氧化是活性污泥处理法的最初步骤。未经处理的污水注入了微生物和原生生物的絮凝剂，并在流经贮水池时充分地加入空气。在五到八小时内，大部分易氧化的有机物被氧化，而且已凝聚的胶状粒子形成了更多的活性污泥。这易于沉淀，而且大约四分之一用于培养液；额外的脱水，用作肥料或在厌氧气体容器中通过缓慢发酵进一步分解。气体形成78%的甲烷---可用于燃气发动机来运行工厂。也可参阅卫生工程---污水处理词条。

Infectious Disease.  In man and animal there is a range of association with bacteria all the way from the transient soil bacteria that may be present on the skin and mucous membranes, through those considered to be normal bacterial inhabitants, to the bacteria that produce infectious disease. The normal flora of the skin and mucous membrane include staphylococci, streptococci, lactobacilli, spirochetes, and Corynebacterium and Neisseria species. Among the normal flora of the intestinal tract are Escherichia coli, Bacteriodes and Clostridium species, lactobacilli, and streptococci. Both diet and oral antibiotic therapy can cause marked changes in the intestinal flora that may lead to disease in the host. Diet may also influence the growth and acid production of lactobacilli of the mouth, leading to dental caries. By contrast, under the usual conditions of host-bacteria interaction, some of the normal flora act to help the host. Examples of the latter activity are the synthesis of vitamins in the intestines by bacteria and the parallel synthesis of protein and vitamins in the rumen of cattle. The normal flora are usually considered to be nonpathogenic, but under unusual conditions they may produce disease. See also PARASITES; PARASITIC DISEASE.

传染病。在人类和动物中，至始至终都存在一系列与细菌的联系，从可能出现在皮肤和黏膜上短暂的土壤细菌，那些被认为是正常细菌的栖息物，到引发传染病的细菌。皮肤和黏膜的正常菌群包括葡萄状球菌，链球菌，乳酸杆菌，螺旋菌和棒状杆菌和奈瑟菌种。在正常的肠道菌群中是大肠杆菌，拟杆菌和梭菌种，乳酸杆菌和链球菌。饮食与口服抗生素会引起肠道菌群的明显变化，可能导致宿主患病。饮食也可能影响口腔乳酸菌的生长和产酸，导致龋齿。相比之下，在宿主菌相互作用的通常条件下，一些正常的菌群会帮助宿主。后者活动的例子是在肠道内由细菌合成的维生素，以及在牛的瘤胃里平行合成的蛋白质和维生素。正常的菌群通常被认为是非致病性的，但在异常的条件下，它们会引发疾病。也可参阅寄生虫；寄生虫病词条。

Host-Bacteria Relationships.  A number of bacteria will produce disease when introduced into a susceptible host. The proof that bacteria can cause disease and subsequent investigation of their mode of action has led to the control of many bacterial diseases. If a bacterium is to cause disease, it must invade a susceptible host, grow, and produce damage.

宿主-细菌关系。许多细菌当引入易感宿主时就会产生疾病。细菌会导致疾病的证据与随后对它们行为模式的调查导致了对许多细菌疾病的控制。如果细菌会致病，那么它必须侵入易感宿主，生长和造成损害。

In the late 19^th century studies of Bacillus anthracis, it was first thought that bacteria caused disease by growing in great numbers and mechanically blocking blood circulation. Eventually it was discovered that some bacteria produce substances that cause damage to body areas distant from the original growth site. These substances, called toxins, are of two types. Exotoxins are soluble poisonous substances liberated from the bacteria during the period of growth; examples of these proteins are the diphtheria toxin of Corynebacterium diphtheria, the tetanus toxin of Clostridium tetani, and the leukocytic toxin (involves leukocytes) and enterotoxin (responsible for gastrointestinal symptoms) of Staphylococcus aureus. The endotoxins of the gram-negative organisms—an example is Salmonella typhosa—are lipoprotein-polysaccharide complexes of the bacterial cell wall that are released only upon the cell’s destruction. Each of the exotoxins has a specific pharmacological action (as, for example, the effect of diphtheria toxin on heart muscle), which accounts for some of the specific symptoms of diseases caused by bacteria that produce this type of toxin. By contrast, regardless of the species of gram-negative bacterium that produces them, all endotoxins (not soluble and only separable by disintegration of the cell body) exert approximately the same pharmacological action, manifested by fever and shock. See also TOXINS.

在十九世纪末对碳疽杆菌的研究中，人们起初认为细菌是通过大量生长并机械地阻塞血液循环导致疾病的。最终人们发现，某些细菌会产生一些物质，会对远离起初生长部位的身体区域造成损害。这些称为毒素的物质有两类。外毒素是从细菌生长期释放出的可溶性有毒物质；这种蛋白质的例子是白喉棒状杆菌的白喉毒素，破伤风梭菌的破伤风毒素，以及白细胞毒素（涉及白血球）和金黄色葡萄球菌的肠毒素（导致胃肠道症状）。革兰氏阴性有机体的内毒素—一个例子是伤寒沙门氏菌---是细菌细胞壁的脂蛋白-多糖的复合物，它只在细胞被摧毁时才释放。每种外毒素具有一种特定的药理作用（例如，像白喉毒素对心肌的影响那样），这就解释了由产生这种毒素的细菌致病的一些特定症状。相比之下，无论产生它们的是哪种革兰氏-阴性细菌，所有的内毒素（不可溶的和只有通过细胞体分裂才可分离的）都发挥大致相同的药理作用，表现为发热和休克。也可参阅毒素词条。

The host responds to invasion by a pathogenic bacterium in a variety of ways. First, there is an accumulation of white blood cells at the initial point of entry. These blood cells act as phagocytes to ingest and digest the bacteria. Blood and tissue fluids also accumulate at the site of infection, and the fluids usually contain much nonspecific substances as basic amino acids that may kill the bacteria later, blood fluids containing proteins called antibodies, which are specific for the particular bacterial species or its toxin, act in a variety of ways to kill or to inhibit the growth of the bacteria. If the bacteria are not eliminated by the actions cited, then metastasis (the spread of the infection to other parts of the host) may take place. If the body defenses can eliminate the pathogenic organism, the host recovers; if the bacterium is not eliminated, the host may die, or a chronic infection may follow. Alternatively, the host may recover clinically, but not bacteriologically, and thus may remain a “carrier.” See also DISEASE, GERM THEORY OF; IMMUNITY.

宿主会以各种方式对致病菌的入侵做出反应。首先，在最初的进入点聚集白血球。这些白血球作为吞噬细胞摄取并消化细菌。血液和组织液也聚集在感染部位，而这些液体通常含有许多碱性氨基酸的非特异性物质，随后会杀灭细菌，血液含有称为抗体的蛋白质，专门针对特定的细菌属或其毒素，以各种方式杀灭或抑制细菌的生长。如果列举的措施未能消灭细菌，那么就可能发生转移（感染扩散到宿主的其它部位）。如果身体防御能消除致病的有机体，那么宿主就会康复；如果没有消灭细菌，宿主可能会死亡，或者留下慢性感染。或者，宿主在临床上恢复了，但在细菌学上并未恢复，因此依然是一个“携带者”。也可参阅疾病的病菌理论；免疫力词条。

Transmission of Infectious Agents.  If a bacterium is to cause disease, it must be transmitted from the infected host or “healthy” carrier to the susceptible individual and must be able to survive this inter-host period. The characteristics of transmission of certain pathogenic bacteria are a reflection of their ability to survive. Anthrax, a disease of cattle and sheep, is caused by a spore—forming bacterium, Bacillus anthracis, which in spore form can persist for many years in the soil. Thus, wherever anthrax has occurred, the disease agent always is present, and possibility of infection persists. Syphilis in man is caused by a bacterium, treponema pallidum, which can survive for only a few hours away from its host and thus generally must be transmitted directly from the infected host to the susceptible individual. Some bacteria are transmitted by insects and will live for long periods of time in these carriers.

传染性病原体的传播。如果一种细菌会引发疾病，那它一定是从受感染的宿主或“健康的”携带者那里传染给易感染的个体，并且在这个中间宿主期间一定能够存活下来。某些致病菌的传播特征是它们生存能力的反映。炭疽热，一种牛和羊的疾病，是由形成细菌的孢子炭疽杆菌引起的，它以孢子形态能在土壤中存在多年。因此，无论碳疽热出现在哪里，病原体就一直存在，而且感染的可能性就会继续存在。人类的梅毒是由梅毒螺旋体细菌引起的，离开其宿主，它只能存活几个小时。因此，通常一定是从已感染的宿主直接传播给易感的个体。一些细菌是通过昆虫传播的，并会在这些载体中存活很长一段时间。

The usual methods of transmission of pathogenic bacteria to a susceptible host are: (1) direct, as by sexual intercourse; (2) indirect, as by food, water, eating utensils, and air; and (3) by insect vectors. It is important to determine the exact method of transmission of each disease agent, for this information can be used to cut the line of transmission and thus control the spread of the disease. For example, the knowledge that Salmonella typhosa, the bacterium of typhoid fever, is spread by contaminated water has led to the development of sanitary engineering procedures that have tended to eliminate the disease. See also CONTAGION AND CONTAGIOUS DISEASES.

致病菌传播给易感宿主的常用方法是：（1）直接方式，如通过性交；（2）间接方式，如通过食物、水、餐具和空气；以及（3）通过昆虫载体。重要的是要确定每种病原体传播的准确方式，因为这一信息可用于切断传播路线，并因此控制该疾病的传播。例如，认识到沙门氏菌，伤寒症细菌是由受到污染水的传播，导致了卫生工程程序的发展，因此易于消除这种疾病。

Disease of Man.  The importance of bacterial diseases is reflected, first, in the number of cases or of deaths resulting from a particular bacterium and, second, in the programs required to keep particular disease agents under control. In the United States, agents in the first category are Staphylococcus aureus (wound infections, pneumonia); Streptococcus pyogenes (septic sore throat, rheumatic fever); Diplococcus pneumonia (pneumonia); Mycobacterium tuberculosis (tuberculosis); Treponema pallidum (syphilis); Neisseria gonorrhoeae (gonorrhea); and Salmonella species (food poisonings and enteric disease).

人类的疾病。细菌性疾病的重要性体现在，首先，在病例或死亡数量上是由特定的细菌造成的，其次，控制特定病原体所需要的程序。在美国，第一类病原体是金黄色酿脓葡萄球菌（伤口感染，肺炎）；酿脓链球菌（脓毒性咽喉炎，风湿热）；肺炎双球菌（肺炎）；结核杆菌（结核病）；梅毒螺旋体（梅毒）；淋病奈瑟氏菌（淋病）；以及沙门氏菌属（食物中毒和肠道疾病）。

Bacterial agents important, not for the number of cases of disease or death, but from the standpoint of public health measures designed to keep them under control are Salmonella typhosa (typhoid fever); vibrio comma (cholera); Shigella dysenteriae (bacterial dysentery); Corynebacterium diphtheria (diphtheria); and Pasteurella pestis (plague). In other areas, particularly in parts of Asia and Africa, bacterial agents of human disease---among them, typhoid fever, cholera, diphtheria, plague, and leprosy—are important both for the number of cases and deaths and also from the viewpoint of the development of programs of control by the World Health Organization of the United Nations and other public and private agencies. See also TROPICAL MEDICINE.

细菌的病原体很重要，不是因为病例或死亡的数量，而是从公共卫生措施的角度来看，目的在于控制它们的是沙门氏菌（伤寒症）；弧菌（霍乱）；以及巴氏德菌鼠疫（腺鼠疫）。在其它地方，尤其是亚洲和非洲的部分地区，人类疾病的细菌病原体---其中有，伤寒症，霍乱，白喉，腺鼠疫和麻风病---对病例和死亡数量，还有从由联合国世界卫生组织以及其它公共和私人机构的控制计划的发展观点来看都很重要。也可参阅热带病学词条。

Diseases of Animals.  Different species, as well as their geographical distribution, must be considered in the discussion of bacterial diseases of animals. From the standpoint of numbers of cases or deaths, some important agents are Staphylococcus aureus (mastitis in dairy cows and joint disease in poultry); Mycobacterium avium (tuberculosis in swine and poultry); Brucella suis (the cause of brucellosis or Traum’s disease, resulting in abortion in swine); Mycoplasma (pleuropneumonia and other diseases in poultry, swine, sheep, and cattle); Leptospira species (leptospirosis in cattle, swine, and dogs); Pasteurella haemolytica (pneumonia in cattle and sheep); Salmonella species (abortion in mares and sheep and other disease in poultry and swine); Erysipelothrix rhusiopathiae (erysipelas in swine); and Escherichia coli (a major cause of death in newborn animals). Bacterial disease agents in animals that are important because of the effort devoted to control procedures are Mycobacterium bovis (tuberculosis in cattle and other animals); Brucella abortus (the cause of brucellosis or Bang’s disease, resulting in abortion in cows); Bacillus anthracis (anthrax in cattle, sheep, and other animals); various Clostridium species(blackleg in cattle and other animal and overeating disease in lamb); and Salmonella gallinarum (bacillary white diarrhea in chickens). See also ANIMAL DISEASES.

动物的疾病。在动物细菌疾病的讨论中，必须考虑不同的种类以及它们的地理分布。从病例或死亡数量角度来看，一些重要的病原体有金黄色酿脓葡萄球菌（奶牛的乳腺炎和家禽的关节病）；鸟分支杆菌（猪和家禽结核病）；猪布鲁氏杆菌（布氏菌病的原因或猪布鲁氏菌病，导致猪流产）；支原菌（家禽、猪、羊和牛的胸膜肺炎和其它疾病）；细螺旋体种类（牛、猪和狗的钩端螺旋体病）；溶血性巴斯德氏菌（牛和羊的肺炎）；沙门氏菌属（马和羊的流产，以及家禽和猪的其它疾病）；猪红斑丹毒丝菌（猪的丹毒）；以及大肠杆菌（新出生动物死亡的主要原因）。由于在控制程序上所付出的努力，在动物中很重要的细菌性病原体有牛结核分枝杆菌（牛和其它动物的结核病）；流产布鲁氏菌（布鲁氏或邦氏病的原因，导致母牛流产）；炭疽杆菌（牛、羊以及其它动物的碳疽热）；各种梭芽孢杆菌（牛和其它动物的黑腿病，以及羔羊的暴食病）；以及鸡伤寒沙门氏菌（鸡的杆状细菌白痢）也可参阅动物疾病词条。

Diseases of Plants.  The major causes of infectious botanical diseases are molds (fungi, q.v.) and viruses. The fungus diseases number in the thousands. Bacterial diseases of plants are, by contrast, restricted to a few hundred, but they remain important, not only because they require the devotion of resources to control and eradicate, but because they regularly destroy sizable proportions of certain crops, force consequent and sudden reductions in the acreage devoted to production, and cause serious economic dislocations. Examples of important bacterial plant pathogens and the diseases they cause are Erwinia amylovora (fireblight of apples and pears); E. carotovora (soft rot of vegetables); Agrobacterium tumefaciens (crown gall of fruits); and Streptomyces scabies (potato scab). See also PLANTS AND PLANT SCIENCE—5. Pathology.

植物的疾病。传染性植物疾病的主要原因是霉菌（参见真菌）和病毒。真菌疾病数以千计。相比之下，植物的细菌疾病只有几百种，但它们依然很重要，不仅是因为它们需要投入资源来控制和根除，而是因为它们经常破坏相当数量的农作物，在生产面积上造成随之而来的影响和突然减少，并且引起严重的经济混乱。重要的细菌植物病原体和它们引发的疾病有解淀粉欧文氏菌（苹果和梨的梨火疫）；胡萝卜软腐欧文氏菌（蔬菜的软腐病）；根癌土壤杆菌（水果的冠瘿）；以及疮痂病链霉菌（马铃薯疮痂病）。也可参阅植物和植物科学词条。

Exobiology.  Bacterial will undoubtedly play a role in the newly developing science of exobiology, the biology of space. If life is found elsewhere, it may well be that of all the organisms of this earth only bacteria could survive the extreme conditions characteristic of the planets nearest us. If we are to establish this, we must be certain that space vehicles sent out from earth do not contaminate the moon or planets. This requires the use of aseptic techniques in the manufacture and assembly of all components of space vehicles, techniques that must be more rigorous even than those used in the operating room. Microorganisms, including bacteria, also may be useful for manned space flight. It is possible to establish a complete cycle of matter by use of microorganisms in a closed system to eliminate carbon dioxide and other wastes of man and to regenerate food supplies from these excreta.

太空生物学。在新发展的太空生物学，空间生物学中细菌将无疑发挥作用。如果在其它地方发现了生命，情况也许是这样，这个地球上所有有机体只有细菌能够生存在离我们最近的行星所特有的极端条件下。如果我们要确立这点，我们必须确定从地球发射的空间飞行器不会污染月球或行星。这需要在制造和组装空间飞行器的所有组件时使用无菌技术，这些技术必须，甚至比手术室中使用的那些技术要更加严格。微生物，包括细菌，也可能对载人空间飞行有用。在一个封闭的系统中利用微生物建立一个完整的物质循环，以消除了二氧化碳和其它人类的废弃物，并从这些排泄物中再生食物供应是可能的。

 

6. Bacteriophage and Bacteriogenetics

In the late 19^th century filters that would retain bacteria were used to help prove that bacteria caused disease. If a fluid that contained an infectious agent lost its infectivity after passage through a filter, then it contained bacteria; if the fluid retained its infectivity, then the disease was caused by a “filterable virus,” a term from the Latin meaning poison. Filterable viruses were found to be the agents of many infectious diseases (see VIRUS).

6、噬菌体和细菌遗传学

    在十九世纪末，那种可保留细菌的过滤装置被用来帮助证明细菌会引发疾病。如果一种遏制传染病原体的液体在通过过滤器的过程后失去了其传染性，那么过滤器就遏制了细菌；如果该液体保留了其传染性，那么该疾病就是由一种“滤过性病毒”引起的，一个来自拉丁语的术语，意思是毒物。滤过性病毒被发现是许多传染性疾病的病原体（见病毒词条）。

In the second decade of the 20^th century, Frederick William Twort and Felix Hubert d’Herelle discovered filterable agents that would lyse (burst) bacterial cells. These agents, named bacteriophage, were subsequently considered to be viruses that attack bacteria. Bacteriophages have been found for most bacteria. A phage is specific for a certain kind of bacterium and is named for the bacterium it will infect. Thus, a phage infecting the bacterium Escherichia coli is called a coli-phage. Phages have a polyhedral head consisting of a protein shell containing nucleic acid and a hollow protein tube for a tail. Phages contain only one of the two kinds of nucleic acid; most phages contain deoxyribonucleic acid (DNA), but a few contain ribonucleic acid.

在20世纪的第二个十年中，弗雷德里克·威廉·特沃特和费力克斯·休伯特·德赫莱尔发现了会分解细菌细胞的滤过性病原体。这些取名为噬菌体的病原体后来被认为是攻击细菌的病毒。大多数细菌都发现了噬菌体。噬菌体针对的是某一种细菌，并以它会感染的细菌来命名。因此，噬菌体感染的细菌大肠杆菌就被称为大肠杆菌噬菌体。噬菌体拥有一个由含有核酸蛋白质外壳组成的多面体头和一个空心的蛋白质管的尾巴。噬菌体只含有两种核酸中的一种；大多数噬菌体含有脱氧核糖核酸（DNA），但少数含有核糖核酸。

Infection occurs when the phage attaches itself by its tail to the bacterial cell and injects the nucleic acid from the head through the hollow tail into the host cell. The phage nucleic acid changes the metabolism of the bacterial cell so that several hundred phage particles are produced, and the bacterial cell finally bursts, releasing the mature phage particles. This is called a lytic phage, and the phage particles are called vegetative phage. Such a phage, when introduced into growth of a bacterium on a solid medium, will cause clear areas to appear where the bacterial cells are lysed. These areas are called plaques. A temperate phage is one that infects a bacterial cell, and the phage DNA becomes part of the genetic mechanism of the cell and replicates at each cell division. This condition is termed lysogeny. The phage DNA is now called a pro-phage, and the bacterial cells are called glycogenic. The prophage may become active to form vegetative phage which is released by bursting of the bacterial cell.

当噬菌体用其尾巴将自身附着在细菌细胞上并从头部将核酸通过空心尾巴注入宿主细胞时就会发生感染。噬菌体核酸改变了细菌细胞的新陈代谢，这样就产生出几百个噬菌体粒子，而且细菌细胞最终会爆发，释放成熟的噬菌体粒子。这被称为溶解性噬菌体，而且该噬菌体粒子被称为营养噬菌体。这样的噬菌体，当细菌在固体培养基上生长时，在细菌细胞被溶解的地方就会导致出现明显的区域。这些区域被称为斑块。温和噬菌体是感染了细菌细胞的一种噬菌体，并且噬菌体DNA变成了细胞遗传机制的一部分，并在每个细胞分裂时复制。这种情况被称为溶原现象。噬菌体DNA现在被称为前噬菌体，而该细菌细胞被称为糖原细胞。前噬菌体可能变得活跃，通过细菌细胞破裂的释放，形成营养噬菌体。

Because of the ease with which bacteria can be grown and infected with phage, much basic information on the biology of the virus-host cell interaction has been developed with the phage-bacterial cell system. In 1920’s there was hope that phages which destroyed disease-producing bacteria could be used in treatment of disease. For example, it was thought that an individual with typhoid fever could be fed some phage that would destroy Salmonella typhosa and that the disease could be cured. Unfortunately, this did not prove to be true. Although phage has been tried in the treatment of a number of bacterial diseases, no serious consideration is now given to this method of therapy.

由于细菌易生长并被噬菌体感染，许多有关病毒-宿主细胞相互作用的生物学基本信息与噬菌体细菌细胞系统一同获得了发展。在20世纪20年代，人们希望消灭产生疾病细菌的那种噬菌体能被用于治疗疾病。例如，人们认为，患有伤寒症的个体可以服用一些会杀灭伤寒沙门氏菌的噬菌体，而且该病可以得到治疗。不幸的是，这一想法未能成真。尽管在治疗许多细菌性疾病中曾尝试过噬菌体，但现在已无人认真地考虑使用这种治疗方法了。

Cytological, biochemical, and genetic studies show that bacteria have a nucleus containing deoxyribonucleic acid (DNA) and that this DNA contains genetic information. (See GENES, NATURE AND ACTION OF.) Because bacteria ordinarily grow by vegetative reproduction (binary fission), change in the genetic material is usually the result of gene mutation. Markers that may be used in genetic studies with bacteria include antibiotic resistance, nutritional requirements, and sugar fermentation. Gene recombination between bacteria can occur by conjugation (brief cytoplasmic union) in which there are recognized donor and recipient cells. Transformation may take place when DNA from one cell is taken in by other cells, which then become genotypically (genetically) a characteristic of the first cell type. Furthermore, genetic material from one bacterium may be introduced into another bacterial cell by a temperate bacteriophage, a bacteria-destroying agent, this process being known as transduction. Finally, a temperate bacteriophage may invade the genetic material of a bacterium and become a pro-phage, and this may be expressed phenotypically in the altered bacterium. This is known as lysogenic conversion.

细胞学，生物化学和遗传学的研究表明，细菌拥有一种含有脱氧核糖核酸（DNA）的细胞核，而且这种DNA含有遗传信息。（见基因的的性质和作用词条）。因为细菌通常通过无性繁殖（二无分裂）来生长，遗传物质的改变通常是基因突变的结果。可用于细菌遗传研究的标记物，包括抗生素的耐药性，营养需求，以及糖发酵。细菌之间的基因重组可通过结合来产生（简短的细胞质联合），其中有公认的供体和受体细胞。当来自一种细胞的DNA被其它细胞所接纳时，就会发生转变，然后成为基因型（与遗传有关的）的第一种细胞类型的特征。此外，来自一种细菌的遗传物质可通过温和的噬菌体，一种杀菌剂，引入另一个细菌细胞中，这一过程被称为转导。最后，温和的噬菌体可以侵入细菌的遗传物质，并变成前噬菌体，而且这可能在改变的细菌中以显形的方式表现出来。这被称为溶源转换。

 

                    PERRY W. WILSON and JOE B. WILSON

                                University of Wisconsin

                         佩里·W. 威尔逊与乔·B. 威尔逊

                                           威斯康星大学

 

                                  2023年1月26日译

（译者注：该词条位列《大美百科全书》1985年版，第3卷，第34页至39页）