《微生物生物学》课程书籍文献：《Microbiology》微生物学PDF电子书（Lansing M. Prescott - McGraw-Hill，Fifth Edition）.pdf_P21-P25

Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 2. The suspected microorganism must be isolated and grown in a pure culture. 3. The same disease must result when the isolated microorganism is inoculated into a healthy host. 4. The same microorganism must be isolated again from the diseased host. Although Koch used the general approach described in the postulates during his anthrax studies, he did not outline them fully until his 1884 publication on the cause of tuberculosis (Box 1.2). Koch’s proof that Bacillus anthracis caused anthrax was independently confirmed by Pasteur and his coworkers. They discovered that after burial of dead animals, anthrax spores survived and were brought to the surface by earthworms. Healthy animals then ingested the spores and became ill. The Development of Techniques for Studying Microbial Pathogens During Koch’s studies on bacterial diseases, it became necessary to isolate suspected bacterial pathogens. At first he cultured bacteria on the sterile surfaces of cut, boiled potatoes. This was unsatisfactory because bacteria would not always grow well on potatoes. He then tried to solidify regular liquid media by adding gelatin. Separate bacterial colonies developed after the surface had been streaked with a bacterial sample. The sample could also be mixed with liquefied gelatin medium. When the gelatin medium hardened, individual bacteria produced separate colonies. Despite its advantages gelatin was not an ideal solidifying agent because it was digested by many bacteria and melted when the temperature rose above 28°C. A better alternative was provided by Fannie 8 Chapter 1The History and Scope of Microbiology Although biologists employ a variety of approaches in conducting research, microbiologists and other experimentally oriented biologists often use the general approach known as the scientific method. They first gather observations of the process to be studied and then develop a tentative hypothesis—an educated guess—to explain the observations (see Box figure). This step often is inductive and creative because there is no detailed, automatic technique for generating hypotheses. Next they decide what information is required to test the hypothesis and collect this information through observation or carefully designed experiments. After the information has been collected, they decide whether the hypothesis has been supported or falsified. If it has failed to pass the test, the hypothesis is rejected, and a new explanation or hypothesis is constructed. If the hypothesis passes the test, it is subjected to more severe testing. The procedure often is made more efficient by constructing and testing alternative hypotheses and then refining the hypothesis that survives testing. This general approach is often called the hypothetico-deductive method. One deduces predictions from the currently accepted hypothesis and tests them. In deduction the conclusion about specific cases follows logically from a general premise (“if . .,then . . .” reasoning). Induction is the opposite. A general conclusion is reached after considering many specific examples. Both types of reasoning are used by scientists. When carrying out an experiment, it is essential to use a control group as well as an experimental group. The control group is treated precisely the same as the experimental group except that the experimental manipulation is not performed on it. In this way one can be sure that any changes in the experimental group are due to the experimental manipulation rather than to some other factor not taken into account. If a hypothesis continues to survive testing, it may be accepted as a valid theory. A theory is a set of propositions and concepts that provides a reliable, systematic, and rigorous account of an aspect of nature. It is important to note that hypotheses and theories are never absolutely proven. Scientists simply gain more and more confidence in their accuracy as they continue to survive testing, fit with new observations and experiments, and satisfactorily explain the observed phenomena. Box 1.1 The Scientific Method The Hypothetico-Deductive Method. This approach is most often used in scientific research. Problem Develop hypothesis Select information needed to test hypothesis Collect information by observation or experiment Analyze information Falsification Hypothesis rejected Construct new hypothesis Hypothesis supported Expose to more tests Eventual falsification Develop new hypothesis incorporating strong points of old hypothesis

Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 Eilshemius Hesse, the wife of Walther Hesse, one of Koch’s assistants (figure 1.5). She suggested the use of agar as a solidifying agent—she had been using it successfully to make jellies for some time. Agar was not attacked by most bacteria and did not melt until reaching a temperature of 100°C. One of Koch’s assistants, Richard Petri, developed the petri dish (plate), a container for solid culture media. These developments made possible the isolation of pure cultures that contained only one type of bacterium, and directly stimulated progress in all areas of bacteriology. Isolation of bacteria and pure culture techniques (pp. 106–10). Koch also developed media suitable for growing bacteria isolated from the body. Because of their similarity to body fluids, meat extracts and protein digests were used as nutrient sources. The result was the development of nutrient broth and nutrient agar, media that are still in wide use today. By 1882 Koch had used these techniques to isolate the bacillus that caused tuberculosis. There followed a golden age of about 30 to 40 years in which most of the major bacterial pathogens were isolated (table 1.1). The discovery of viruses and their role in disease was made possible when Charles Chamberland (1851–1908), one of Pasteur’s associates, constructed a porcelain bacterial filter in 1884. The first viral pathogen to be studied was the tobacco mosaic disease virus (see chapter 16). The development of virology (pp. 362–63). Immunological Studies In this period progress also was made in determining how animals resisted disease and in developing techniques for protecting humans and livestock against pathogens. During studies on chicken cholera, Pasteur and Roux discovered that incubating their cultures for long intervals between transfers would attenuate the bacteria, which meant they had lost their ability to cause the disease. If the chickens were injected with these attenuated cultures, they remained healthy but developed the ability to resist the disease. He called the attenuated culture a vaccine [Latin vacca, cow] in honor of Edward Jenner because, many years earlier, Jenner had used vaccination with material from cowpox lesions to protect people against smallpox (see section 16.1). Shortly after this, Pasteur and Chamberland developed an attenuated anthrax vaccine in two ways: by treating cultures with potassium bichromate and by incubating the bacteria at 42 to 43°C. Vaccines and immunizations (pp. 764–68). 1.3 The Role of Microorganisms in Disease 9 Although the criteria that Koch developed for proving a causal relationship between and a microorganism and a specific disease have been of immense importance in medical microbiology, it is not always possible to apply them in studying human diseases. For example, some pathogens cannot be grown in pure culture outside the host; because other pathogens grow only in humans, their study would require experimentation on people. The identification, isolation, and cloning of genes responsible for pathogen virulence (see p. 794) have made possible a new molecular form of Koch’s postulates that resolves some of these difficulties. The emphasis is on the virulence genes present in the infectious agent rather than on the agent itself. The molecular postulates can be briefly summarized as follows: 1. The virulence trait under study should be associated much more with pathogenic strains of the species than with nonpathogenic strains. Box 1.2 Molecular Koch’s Postulates 2. Inactivation of the gene or genes associated with the suspected virulence trait should substantially decrease pathogenicity. 3. Replacement of the mutated gene with the normal wild-type gene should fully restore pathogenicity. 4. The gene should be expressed at some point during the infection and disease process. 5. Antibodies or immune system cells directed against the gene products should protect the host. The molecular approach cannot always be applied because of problems such as the lack of an appropriate animal system. It also is difficult to employ the molecular postulates when the pathogen is not well characterized genetically. Figure 1.5 Fannie Eilshemius (1850–1934) and Walther Hesse (1846–1911). Fannie Hesse first proposed using agar in culture media

Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 Pasteur next prepared rabies vaccine by a different approach. The pathogen was attenuated by growing it in an abnormal host, the rabbit. After infected rabbits had died, their brains and spinal cords were removed and dried. During the course of these studies, Joseph Meister, a nine-year-old boy who had been bitten by a rabid dog, was brought to Pasteur. Since the boy’s death was certain in the absence of treatment, Pasteur agreed to try vaccination. Joseph was injected 13 times over the next 10 days with increasingly virulent preparations of the attenuated virus. He survived. In gratitude for Pasteur’s development of vaccines, people from around the world contributed to the construction of the Pasteur Institute in Paris, France. One of the initial tasks of the Institute was vaccine production. After the discovery that the diphtheria bacillus produced a toxin, Emil von Behring (1854–1917) and Shibasaburo Kitasato (1852–1931) injected inactivated toxin into rabbits, inducing them to produce an antitoxin, a substance in the blood that would inactivate the toxin and protect against the disease. A tetanus antitoxin was then prepared and both antitoxins were used in the treatment of people. The antitoxin work provided evidence that immunity could result from soluble substances in the blood, now known to be antibodies (humoral immunity). It became clear that blood cells were also important in immunity (cellular immunity) when Elie Metchnikoff (1845–1916) discovered that some blood leukocytes could engulf disease-causing bacteria (figure 1.6). He called these cells phagocytes and the process phagocytosis [Greek phagein, eating]. 1. Discuss the contributions of Lister, Pasteur, and Koch to the germ theory of disease and to the treatment or prevention of diseases. 2. What other contributions did Koch make to microbiology? 3. Describe Koch’s postulates. What are the molecular Koch’s postulates and why are they important? 4. How did von Behring and Metchnikoff contribute to the development of immunology? 1.4 Industrial Microbiology and Microbial Ecology Although Theodore Schwann and others had proposed in 1837 that yeast cells were responsible for the conversion of sugars to alcohol, a process they called alcoholic fermentation, the leading chemists of the time believed microorganisms were not involved. They were convinced that fermentation was due to a chemical instability that degraded the sugars to alcohol. Pasteur did not agree. It appears that early in his career Pasteur became interested in fermentation because of his research on the stereochemistry of molecules. He believed that fermentations were carried out by living organisms and produced asymmetric products such as amyl alcohol that had optical activity. There was an intimate connection between molecular asymmetry, optical activity, and life. Then in 1856 M. Bigo, an industrialist in Lille, France, where Pasteur worked, requested Pasteur’s assistance. His business produced ethanol from the fermentation of beet sugars, and the alcohol yields had recently declined and the product had become sour. Pasteur discovered that the fermentation was failing because the yeast normally responsible for alcohol formation had been replaced by microorganisms producing lactic acid rather than ethanol. In solving this practical problem, Pasteur demonstrated that all fermentations were due to the activities of specific yeasts and bacteria, and he published several papers on fermentation between 1857 and 1860. His success led to a study of wine diseases and the development of pasteurization (see chapter 7) to preserve wine during storage. Pasteur’s studies on fermentation continued for almost 20 years. One of his most important discoveries was that some fermentative microorganisms were anaerobic and could live only in the absence of oxygen, whereas others were able to live either aerobically or anaerobically. Fermentation (pp. 179–81); The effect of oxygen on microorganisms (pp. 127–29). A few of the early microbiologists chose to investigate the ecological role of microorganisms. In particular they studied microbial involvement in the carbon, nitrogen, and sulfur cycles taking place in soil and aquatic habitats. Two of the pioneers in this endeavor were Sergei N. Winogradsky (1856–1953) and Martinus W. Beijerinck (1851–1931). Biogeochemical cycles (pp. 611–18). 10 Chapter 1The History and Scope of Microbiology Figure 1.6 Elie Metchnikoff. Metchnikoff (1845–1916) shown here at work in his laboratory

Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 The Russian microbiologist Sergei N. Winogradsky made many contributions to soil microbiology. He discovered that soil bacteria could oxidize iron, sulfur, and ammonia to obtain energy, and that many bacteria could incorporate CO2 into organic matter much like photosynthetic organisms do. Winogradsky also isolated anaerobic nitrogen-fixing soil bacteria and studied the decomposition of cellulose. Martinus W. Beijerinck was one of the great general microbiologists who made fundamental contributions to microbial ecology and many other fields. He isolated the aerobic nitrogenfixing bacterium Azotobacter; a root nodule bacterium also capable of fixing nitrogen (later named Rhizobium); and sulfatereducing bacteria. Beijerinck and Winogradsky developed the enrichment-culture technique and the use of selective media (see chapter 5), which have been of such great importance in microbiology. 1. Briefly describe the work of Pasteur on microbial fermentations. 2. How did Winogradsky and Beijerinck contribute to the study of microbial ecology? 1.5 Members of the Microbial World Although the kingdoms of organisms and the differences between procaryotic and eucaryotic cells are discussed in much more detail later, a brief introduction to the organisms a microbiologist studies is given here. Comparison of procaryotic and eucaryotic cells (pp. 91–92). Two fundamentally different types of cells exist. Procaryotic cells [Greek pro, before, and karyon, nut or kernel; organism with a primordial nucleus] have a much simpler morphology than eucaryotic cells and lack a true membrane-delimited nucleus. All bacteria are procaryotic. In contrast, eucaryotic cells [Greek eu, true, and karyon, nut or kernel] have a membrane-enclosed nucleus; they are more complex morphologically and are usually larger than procaryotes. Algae, fungi, protozoa, higher plants, and animals are eucaryotic. Procaryotic and eucaryotic cells differ in many other ways as well (see chapter 4). The early description of organisms as either plants or animals clearly is too simplified, and for many years biologists have divided organisms into five kingdoms: the Monera, Protista, Fungi, Animalia, and Plantae (see chapter 19). Microbiologists study primarily members of the first three kingdoms. Although they are not included in the five kingdoms, viruses are also studied by microbiologists. Fungi (chapter 25); Algae (chapter 26); Protozoa (chapter 27); Introduction to the viruses (chapters 16–18) In the last few decades great progress has been made in three areas that profoundly affect microbial classification. First, much has been learned about the detailed structure of microbial cells from the use of electron microscopy. Second, microbiologists have determined the biochemical and physiological characteristics of many different microorganisms. Third, the sequences of nucleic acids and proteins from a wide variety of organisms have been compared. It is now clear that there are two quite different groups of procaryotic organisms: Bacteria and Archaea. Furthermore, the protists are so diverse that it may be necessary to divide the kingdom Protista into three or more kingdoms. Thus many taxonomists have concluded that the fivekingdom system is too simple and have proposed a variety of alternatives (see section 19.7). The differences between Bacteria, Archaea, and the eucaryotes seem so great that many microbiologists have proposed that organisms should be divided among three domains: Bacteria (the true bacteria or eubacteria), Archaea1 , and Eucarya (all eucaryotic organisms). This system, which we shall use here, and the results leading to it are discussed in chapter 19. 1. Describe and contrast procaryotic and eucaryotic cells. 2. Briefly describe the five-kingdom system and give the major characteristics of each kingdom. 1.6 The Scope and Relevance of Microbiology As the scientist-writer Steven Jay Gould emphasized, we live in the Age of Bacteria. They were the first living organisms on our planet, live virtually everywhere life is possible, are more numerous than any other kind of organism, and probably constitute the largest component of the earth’s biomass. The whole ecosystem depends on their activities, and they influence human society in countless ways. Thus modern microbiology is a large discipline with many different specialties; it has a great impact on fields such as medicine, agricultural and food sciences, ecology, genetics, biochemistry, and molecular biology. For example, microbiology has been a major contributor to the rise of molecular biology, the branch of biology dealing with the physical and chemical aspects of living matter and its function. Microbiologists have been deeply involved in studies on the genetic code and the mechanisms of DNA, RNA, and protein synthesis. Microorganisms were used in many of the early studies on the regulation of gene expression and the control of enzyme activity (see chapters 8 and 12). In the 1970s new discoveries in microbiology led to the development of recombinant DNA technology and genetic engineering. The mechanisms of DNA, RNA, and protein synthesis (chapters 11 and 12); Recombinant DNA and genetic engineering (chapter 14) One indication of the importance of microbiology in the twentieth century is the Nobel Prize given for work in physiology or medicine. About 1/3 of these have been awarded to scientists working on microbiological problems (see inside front cover). 1.6 The Scope and Relevance of Microbiology 11 1 Although this will be discussed further in chapter 19, it should be noted here that several names have been used for the Archaea. The two most important are archaeobacteria and archaebacteria. In this text, we shall use only the name Archaea for sake of clarity and consistency

Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 Microbiology has both basic and applied aspects. Many microbiologists are interested primarily in the biology of the microorganisms themselves (figure 1.7). They may focus on a specific group of microorganisms and be called virologists (viruses), bacteriologists (bacteria), phycologists or algologists (algae), mycologists (fungi), or protozoologists (protozoa). Others are interested in microbial morphology or particular functional processes and work in fields such as microbial cytology, microbial physiology, microbial ecology, microbial genetics and molecular biology, and microbial taxonomy. Of course a person can be thought of in both ways (e.g., as a bacteriologist who works on taxonomic problems). Many microbiologists have a more applied orientation and work on practical 12 Chapter 1The History and Scope of Microbiology Figure 1.7 Some Well-Known Modern Microbiologists. This figure depicts a few microbiologists who have made significant contributions in different areas of microbiology. (a) Rita R. Colwell has studied the genetics and ecology of marine bacteria such as Vibrio cholerae and helped establish the field of marine biotechnology. (b) R. G. E. Murray has contributed greatly to the understanding of bacterial cell envelopes and bacterial taxonomy. (c) Stanley Falkow has advanced our understanding of how bacterial pathogens cause disease. (d) Martha Howe has made fundamental contributions to our knowledge of the bacteriophage Mu. (e) Frederick C. Neidhardt has contributed to microbiology through his work on the regulation of E. coli physiology and metabolism, and by coauthoring advanced textbooks. (f) Jean E. Brenchley has studied the regulation of glutamate and glutamine metabolism, helped found the Pennsylvania State University Biotechnology Institute, and is now finding biotechnological uses for psychrophilic (cold-loving) microorganisms. (a) (b) (c) (d) (e) (f )