(Test Bank) Burton's Microbiology For The Health Sciences

Engelkirk,Burton, 8

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Author(s): Engelkirk, Burton

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Page 1 of 1 10/5/2009 http://ecx.ima ges-amazon.com/ima ges/I/51VRNWXMKJL. _SS500 _.jpg1 Microbiology: The Science Learning Objectives AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO: Define microbiology, pathogen, nonpathogen, and opportunistic pathogen List several reasons why microorganisms are important (e.g., as a source of antibiotics) Explain the relationship between microorganisms and infectious diseases Differentiate between infectious diseases and microbial intoxications Outline some of the contributions of Leeuwenhoek, Pasteur, and Koch to microbiology Differentiate between biogenesis and abiogenesis Explain the germ theory of disease Outline Koch's postulates and cite some circumstances in which they may not apply Discuss two medically related fields of microbiology Introduction Welcome to the fa scinating world of microbiology, where yo u will learn about creatu res so small that they cannot be seen with the naked eye. In this chapter, you will discover the effects that these organisms have on our daily lives and the environment around us, and why knowledge of them is of great importance to health care profession als. You will learn that some of these tiny creatures are our friends, whereas others are our enemies. You are about to embark on an exciting journey. Enjoy the adventure! What Is Microbiology? A microbiology course is an advanced biology course. Ideally, students taking microbiology should have some background in biology. As you know, biology is the study of living organisms (from bios , referring to livin g organisms, and logy , meaning “the study of”). Micro means very small—anything so small that it must be viewed with a microscope (an optical instrument used to observe very small objects). Therefore, microbiology is the study of very small living organisms—organisms called microorganisms or microbes. Microorganisms are said to be ubiquitous , meaning they are virtually everywhere. The various categories of microorganisms include viruses, bacteria, archaeans, some algae, protozoa, and some fungi (Fig. 1-1). These categories of microorganisms are discussed in detail in Chapters 4 and 5. Because most scientists do not consider viruses to be living organisms, they are often referred to as “infectious agents” or “infectious particles,” rather than microorganisms. Your first introduction to microorganisms may have been when your mother warned you about “germs” (Fig. 1-2). Although not a scientific term, “germs” are the microorganisms that cause disease. Your mother worried that you might become infected with these types of microorganisms. Disease-causing microorganisms are technically known as pathogens (Table 1-1). Actually, only about 3% of known microbes are capable of causing disease (i.e., only about 3% are pathogenic). Thus, the vast majority of known microorganisms are nonpathogens —microorganisms that do not cause disease. P.2Page 1 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Some of the nonpathogens are beneficial to us and some have no effect on us at all. In newspapers and on television, we read and hear more about pathogens than we do about nonpathogens, but in this book you will learn about bo th categories—the microo rganisms that help us (“microbial allies”) and those that harm us (“microbial enemies”). Why Study Microbiology? Although they are very small, microorganisms play significant roles in our lives. Listed below are a few of the many reasons to take a microbiology course and to learn about microorganisms: Figure 1-1. Family tree of microorganisms. Cellular microorganisms are divided into eucaryotes (organisms having a true nucleus, such as algae, fungi, and protozoa) and procaryotes (organisms lacking a true nucleus, such as archaeans and bacteria). Viruses are not considered to be cells (they are said to be acellular) and are, therefore, not included on this family tree. (The various categories of microorganisms are described in Chapters 4 and 5.) Page 2 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...We have, living on and in our bodies (e.g., on our skin and in our mouths and intestinal tract), approximately 10 times as many microorganisms as the total number of cells (i.e., epithelial cells, nerve cells, muscle cells, etc.) that make up our bodies (10 trillion cells × 10 = 100 trillion microbes). It has been estimated that perhaps as many as 500 to 1,000 different species of microorganisms live on and in us. Collectively, these microbes are known as our indigenous microflora (or indigenous microbiota) and, for the most part, they are beneficial to us. For example, the indigenous microflora inhibit the growth of pathogens in those areas of the body where they live by occupying space, depleting the food supply, and secreting materials (waste products, toxins, antibiotics, etc.) that may prevent or reduce the growth of pathogens. Indigenous microflora are discussed more fully in Chapter 10. P.3 Figure 1-2. Germs. In all likelihood, your mother was your first microbiology Page 3 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Some of the organisms that colonize (inhabit) our bodies are known as opportunistic pathogens (or opportunists ). Although such organisms do not usually cause us any problems, they have the potential to cause infections if they gain access to a part of our anatomy where they do not belong. For example, a bacterium called Escherichia coli (E. coli ) lives in our intestinal tracts. This organism does not cause us any harm as long as it stays in our intestinal tract, but can cause disease if it gains access to our urinary bladder, bloodstream, or a wound. Other opportunistic pathogens strike when a person becomes run down, stressed out, or debilitated (weakened) as a result of some disease or cond ition. Opportunisti c pathogens can be thought of as microorganisms awaiting the opportunity to cause disease. Microorganisms are essential for life on this planet as we know it. For example, some microbes produce oxygen by the process known as photosynthesis (discussed in Chapter 7). Actually, microorganisms contribute more oxygen to our atmosphere than do plants. Thus, organisms that require oxygen—humans, for example—owe a debt of gratitude to the algae and cyanobacteria (a group of photosynthetic bacteria) that produce oxygen. instructor. Not only did she alert you to the fact that there were “invisible” critters in the world that could harm you, she also taught you the fundamentals of hygiene— like handwashing. P.4 TABLE 1-1 Patho gens CATEGOR YEXAMPLES OF DISEASES THEY CAUSE Algae A very rare cause of infections; intoxications (whi ch result from ingestion of toxins) Bacteria Anthrax, botulism, cholera, diarrhea, diphtheria, ear and eye infections, food poisoning, gas gangrene, gonorrhea, hemolytic uremic syndrome (HUS), intoxications, Legionnaires' disease, leprosy, Lyme disease, meningitis, plague, pneumonia, Rocky Mountain spotted fever, scarlet fever, staph in fections, strep throat, syphilis, tetanus, tuberculosis, tularemia, typhoid fever, typhus, urethritis, urinary tract infections, whooping cough Fungi Allergies, cryptococcosi s, histoplasmosis, intoxications, meningitis, pneumonia, thrush, tinea (ringworm) infections, yeast vaginitis Protozoa African sleeping sickness, amebic dysentery, babesiosis, Chagas' disease, cryptosporidiosis, diarrhea, giardiasis, malaria, meningoencephalitis, pneumonia, toxoplasmosis, trichomoniasis Viruses Acquired immunodeficiency syndrome (AIDS), “bird flu,” certain types of cancer, chickenpox, cold sores (fever blisters), common cold, dengue, diarrhea, encephalitis, genital herpes infections, German measles, hantavirus pulmonary syndrome (HPS), hemorrhagic fevers, hepatitis, infectious mononucleosis, influenza, measles, meningitis, mumps, pneumonia, polio, rabies, severe Page 4 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Many microorganisms are involved in the decomposition of dead organisms and the waste products of living organisms. Collectively, they are referred to as decomposers or saprophytes. By definition, a saprophyte is an organism that lives on dead or decaying organic matter. Imagine living in a world with no decomposers. Not a pleasant thought! Saprophytes aid in fertilization by returning inorganic nutrients to th e soil. They break down dead and dying organic materials (plants and animals) into nitrates, phosphates, and other chemicals necessary for the growth of plants (Fig. 1-3). Some microorganisms are capable of decomposing industrial wa stes (oil spills, for example). Thus, we can use microorganisms—genetically engineered microbes, in some cases—to clean up after ourselves. The use of microorganisms in this manner is called bioremediation , a topic discussed in more detail in Chapter 10. Genetic engineering is discussed briefly in this section and more fully in Chapter 7. Many microorganisms are involved in elemental cycles (e.g., carbon, nitrogen, oxygen, sulfur, and phosphorous cycles). In the nitrogen cycle, certain bacteria convert nitrogen gas in the air to ammonia in the soil. Other soil bacteria then convert th e ammonia to nitrites and nitrates. Still other bacteria convert the nitrogen in nitrates to nitrogen gas, thus completing the cycle (Fig. 1-4). Knowledge of these microbes is important to farmers who practice crop rotation to replenish nutrients in their fi elds and to gard eners who keep compost pits as a source of natural fertilizer. In both cases, dead organic material is broken down into inorganic nutrients (e.g., nitrates and phosphates) by microorganisms. The study of the relationships between microbes and the environment is called microbial ecology. Microbial ecology, the nitrogen cycle, and other elemental cycles are discussed more fully in Chapter 10. Algae and bacteria serve as food for tiny animals. Then, larger animals eat the smaller creatures, and so on. Thus, microbes serve as important links in food chains (Fig. 1-5). Microscopic organisms in the ocean, collectively referred to as plankton , serve as the starting point of many food chains. Tiny marine plants and algae are called phytoplankton , whereas tiny marine animals are called zooplankton. Some microorganisms live in the intestinal tracts of animals, where they aid in the digestion of food and, in some cases, produce substances that are of value to the host animal. For example, the E. coli bacteria that live in the human intestinal tract produce vitamins K and B1, which are absorbed and used by the human body. Although termites eat wood, they cannot digest wood. Fortunately for them, termites have cellulose-eating protozoa in their intestinal tracts that break down the wood that the termites consume into smaller molecules that the termites can use as nutrients. acute respiratory syndrome (SARS), shingles, smallpox, warts, yellow fever P.5Page 5 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Many microorganisms are essential in various food and beverage industries, whereas others are used to produce certain enzymes and chemicals (Table 1-2). The use of microorganisms in industry is called biotechnology , a topic discussed more fully in Chapter 10. Figure 1-3. Saprophytes break down dead and decaying organic material into inorganic nutrients in the soil. Figure 1-4. Nitrogen fixation. Nitrogen-fixing bacteria that live on or near the roots of legumes convert free nitrogen from the air into ammonia in the soil. Nitrifying bacteria then convert the ammonia into nitrites and nitrates, which are nutrients used by plants. Page 6 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Some bacteria and fungi produce antibiotics that are used to treat patients with infectious diseases. By definition, an antibiotic is a substance produced by a microorganism that is effective in killing or inhibiting the growth of other microorganisms. The use of microbes in the antibiotic industry is another example of biotechnology. Production of antibiotics by microorganisms is discussed in Chapters 9 and 10. Microbes are essential in the field of genetic engineering. In genetic engineering, a gene from one organism (e.g., from a bacterium, a human, an animal, or a plant) is inserted into a bacterial or yeast cell. Because a gene contains the instructions for the production of a gene product (usually a protein), the cell that receives the new gene can now produce whatever product is coded for by that gene; so too can all of the cells that arise from the original cell. Microbiologists have engineered bacteria and yeasts to produce a variety of useful substances, such as insulin, various types of growth hormones, interferons, and materials for use as vaccines. Genetic engineering is discussed more fully in Chapter 7. For many years, microbes have been used as “cell models.” The more that scientists learned about the structure and functions of microbial cells, the more they learned about cells in general. The intestinal bacterium E. coli is one of the most studied of all microbes. By studying E. coli , scientists have learned a great deal about the composition and inner workings of cells, including human cells. P.6 Figure 1-5. Food chain. Tiny living organisms such as bacteria, algae, microscopic aquatic plants (e.g., phytoplankton), and microscopic aquatic animals (e.g., zooplankton) are eaten by larger animals, which in turn are eaten by still larger animals, etc., until an animal in the chain is consumed by a human. Humans are at the top of the food chain. TABLE 1-2 Products Requiring Microbia l Participation in the Manufacturing Process CATEGOR Y EXAMPLES Foods Acidophilus milk, bread, butter, buttermilk, chocolate, coffee, cottage cheese, cream cheese, fish sauces, green olives, kimchi (from cabbage), meat products (e.g., country-cured hams, sausage, salami), pickles, poi (fermented taro root), sauerkraut, sour cream, sourdough bread, soy sauce, various cheeses (e.g., cheddar, Swiss, Limburger, Camembert, Page 7 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Finally, we come to diseases. Microorganisms cause two categories of diseases: infectious diseases and microbial intoxications (Fig. 1-6). An infectious disease results when a pathogen colonizes the body and subsequently causes disease. A microbial intoxication results when a person ingests a toxin (poisonous substance) that has been produced by a microorganism. Of the two categories, infectious di seases cause far more illnesses and deaths. Infectious diseases are the leading cause of death in the world and the third leading cause of death in the United States (after heart disease and cancer). Worldwide, infectious diseases cause about 50,000 deaths per day; the majority of deaths occur in developing countries. Anyone pursuing a career in a healthcare profession must be aware of infectious diseases, the pathogens that cause them, the sources of the pathogens, how these diseases are transmitted, and how to protect yourself and your patients from these diseases. Physicians' assistants, nurses, dental assistants, laboratory technologists, respiratory therapists, orderlies, nurses' aides, and all others who are associated with patients and patient care must take precautions to prevent the spread of pathogens. Harmful microorganisms may be transferred from health workers to patients; from patient to patient; from contaminated mechanical devices, instruments, and syringes to patients; from contaminated bedding, clothes, dishes, and food to patients; and from patients to healthcare workers, hospital visitors, and other susceptible persons. To limit the spread of pathogens, sterile, aseptic, and antiseptic techniques (discussed in Chapter 12) are used everywhere in hospitals, nursing homes, operating rooms, and laboratories. In addition, the bioterrorist activities of recent years serve to remind us that everyone should have an understanding of the agents (pathogens) that are involved and how to protect ourselves from becoming infected. Bioterrorist and biological warfare agents are discussed in Chapter 11. Additional information about microbial intoxications can be found in CD-ROM Appendix 1 (“Microbial Intoxications”). Roquefort and other blue cheeses), vinegar, yogurt Alcoholic beveragesAle, beer, brandy, sake (rice wine ), rum, sherry, vodka, whiskey, wine Chemicals Acetic acid, acetone, butanol, ci tric acid, ethanol, formic acid, glycerol, isopropanol, lactic acid Antibiotics Amphotericin B, bacitracin, cephalosporins, chloramphenicol, cycloheximide, cycloserine, er ythromycin, griseofulvin, kanamycin, lincomycin, neomycin, novobiocin, nystatin, penicillin, polymyxin B, st reptomycin, tetracycline P.7Page 8 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...First Microorganisms on Earth Perhaps you have wondered how long microorganisms have existed on earth. Scientists tell us that the earth was formed abo ut 4.5 billion years ago and, for the first 800 million to 1 billion years of earth's existence, there was no life on this planet. Fossils of primitive microorganisms (as many as 11 different types) found in ancient rock formations in northwestern Australia date back to about 3.5 billion years ago. By comp arison, animals and huma ns are relative newcome rs. Animals made their appearance on Ea rth between 900 and 650 milli on years ago (there is so me disagreement in the scientific community about the exact date), and, in their present form, humans ( Homo sapiens ) have existed for only the past 100,000 years or so. Candidates for the first microorganisms on earth are archaeans and cyanobacteria; these microorganisms are discussed in Chapter 4. Earliest Known Infectious Diseases In all likelihood, infectious diseases of humans and animals have existed for as long as humans and animals have inhabited the planet. We know that human pathogens have existed for thousands of years because damage caused by them has been observed in the bones and internal organs of mummies and early human fossils. By studying mummies, scientists have learned that bacterial diseases, such as tuberculosis and syphilis, and parasitic worm infections, such as schistosomiasis, dracunculiasis (guinea worm infection), and tapeworm infections, have been around for a very long time. The earliest known account of a “pestilence” occurred in Egypt about 3180 BC. This may represent the first recorded epidemic, although words like “pestilence” and “plague” were used without definition in early writings. Around 1900 BC, near the end of the Trojan War, the Greek army was decimated by an epidemic of what is thought to have been bubonic plague. The Ebers papyrus, describing epidemic fevers, was discovered in a tomb in Thebes, Egypt; it was written around 1500 BC. A disease thought to be smallpox occurred in China around 1122 BC. Epidemics of plague occurred in Rome in 790, 710, and 640 BC and in Greece around 430 BC. In addition to the diseases already mentioned, there are early accounts of rabies, anthrax, dysentery, smallpox, ergotism, botuli sm, measles, typhoid fever, typhus fever, diphtheria , and syphilis. The syphilis story is quite interesting. It made its first appearance in Eu rope in 1493. Many people believe Figure 1-6. The two categories of diseases caused by pathogens. Infectious diseases result when a pathogen colonizes (inhabits) the body and subsequently causes disease. Microbial intoxications result when a person ingests a toxin (poisonous substance) that has been produced by a microorganism in vitro (outside the body). Page 9 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...that syphilis was carried to Europe by Native Americans who were brought to Portugal by Christopher Columbus. The French called syphilis the Neap olitan disease; the Italians called it the French or Spanish disease; and the English called it the French pox. Ot her names for syphilis were Spanish, German, Polish, and Turkish pocks. The name “ syphilis” was not given to the disease until 1530. Pioneers in the Science of Microbiology Bacteria and protozoa were the first microorganisms to be observed by humans. It then took about 200 years before a connection was established between microorganisms and infectious diseases. Among the most significant events in the early history of microbiology were the development of microscopes, bacterial staining procedures, techniques that enabled microorganisms to be cultured in the laboratory; and steps that could be taken to prove that specific microorganisms were responsible for specific infectious diseases. During the past 400 years, many individuals contributed to our present understanding of microorganisms. Three early microbiologists are discussed in this chapter; others are discussed at appropriate points throughout the book. Anton van Leeuwenhoek (1632–1723) Because Anton van Leeuwenhoek was the first person to see live bacteria and protozoa, he is sometimes referred to as the “Father of Microbiology,” the “Father of Bacteriology,” and the “Father of Protozoology.” Interestingly, Leeuwenhoek was not a trained scientist. At various times in his life he was a fabric merchant, a surveyor, a wine assayer, and a minor city official in Delft, Holland. As a hobby, he ground tiny glass lenses, which he mounted in small metal frames, thus creating what today are known as single-lens microscopes or simple microscopes. During his lifetime, he made more than 500 of these microscopes. Leeuwenhoek's fine art of grinding lenses that would magnify an object to 200 to 300 times its size was lost at his death because he had not taught this skill to anyone during his lifetime. In one of the hundreds of letters that he sent to the Royal Society of London, he wrote: My method for seeing the very smallest animalcules I do not impart to others; nor how to see very many animalcules at one time. This I keep for myself alone. Apparently, Leeuwenhoek had an unquenchable curiosity, as he used his microscopes to examine almost anything he could get his hands on (Fig. 1-7). He examined scrapings from his teeth, water from ditches and ponds, water in which he had soaked peppercorns, blood, sperm, and even his own diarrheal stools; in many of these specimens he observed a variety of tiny living creatures, which he called “animalcules.” Leeuwenhoek recorded his observations in the form of letters, which he sent to the Royal Society of London. The following passage is an excerpt from one of those letters ( Milestones in Microbiology , edited by Thomas Brock. American Society for Microbiology, Washington, DC, 1961): Tho my teeth are kept usually very clean, nevertheless when I view them in a Magnifying Glass, I find growing between them a little white matter as thick as wetted flower … I therefore took some of this flower and mixt it … with pure rain water wherein were no Animals … and then to my great surprize perceived that the aforesaid matter contained very many small living Animals, which moved themselves very extravagantly … The number of these Animals in the scurf of a mans Teeth, are so many that I believe they exceed the number of Men in a kingdom. For upon the examination of a small parcel of it, no thicker than a Horse-hair, I found too many living Animals therein, that I guess there might have been 1000 in a quantity of matter no bigger than the 1/100 part of a sand. P.8 Page 10 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Leeuwenhoek's letters finally convinced scientists of the late 17th century of the existence of microorganisms. Leeuwenhoek never speculated on the origin of these microbes, nor did he associate them with the cause of disease. Such relationships were not established until the work of Louis Pasteur and Robert Koch in the late 19th century. The following quote is from Paul de Kruif's book, Microbe Hunters , Harcourt Brace, 1926: [Leeuwenhoek] had stolen and peeped into a fantastic sub-visible world of little things, creatures that had lived, had bred, had battled, had died, completely hidden from and unknown to all men from the beginning of time. Beasts these were of a kind that ravaged and annihilated whole races of men ten million times larger than they were themselves. Beings these were, more terrible than fire-spitting dragons or hydra-headed monsters. They were silent assassins that murdered babes in warm cradles and kings in sheltered places. It was this invisible, insignificant, but implac able—and sometimes friendly—world that Leeuwenhoek had looked into for the first time of all men of all countries. Once scientists became convinced of the existence of tiny creatures that could not be observed with the naked eye, they began to speculate on their origin. On the basis of observation, many of the scientists of that time believed that life could develop spontaneously from inanimate substances, such as decaying corpses, soil, and swamp gases. The idea that life can arise spontaneously from nonliving material is called the theory of spontaneous generation or abiogenesis. For more than two centuries, from 1650 to 1850, this theory was debated and tested. Following the work of others, Louis Pasteur (discussed below) and John Tyndall (discussed in Chapter 3) finally disproved the theory of spontaneous generation and proved that life can only arise from preexisting life. This is called the theory of biogenesis , first proposed by a German scientist named Rudolf Virchow in 1858. Note that the theory of biogenesis does not speculate on the origin of life, a subject that has been discussed and Figure 1-7. Anton van Leeuwenhoek using one of his single-lens microscopes. P.9Page 11 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...debated for hundreds of years. Louis Pasteur (1822–1895) Louis Pasteur (Fig. 1-8), a French chemist, made numerous contributions to the newly emerging field of microbiology and, in fact, his contributions are considered by many people to be the foundation of the science of microbiology and a cornerstone of modern medicine. Listed below are some of his most significant contributions: While attempting to discover why wine becomes contaminated with undesirable substances, Pasteur discovered what occurs during alcoholic fermentation. (Fermentation is discussed in Chapter 7.) He also demonstrated that different types of microorganisms produce different fermentation products. For example, yeasts convert the glucose in grapes to ethyl alcohol (ethanol) by fermentation, but certain contaminating bacteria, such as Acetobacter , convert glucose to acetic acid (vinegar) by fermentation, thus, ruining the taste of the wine. Through his experiments, Pasteur dealt the fatal blow to the theory of spontaneous generation. Pasteur discovered forms of life that could exist in the absence of oxygen. He introduced the terms “aerobes” (organisms that require oxygen) and “anaerobes” (organisms that do not require oxygen). Pasteur developed a process (today known as pasteurization) to kill microbes that were causing wine to spoil—an econ omic concern to France's wine industry. Pasteurization can be used to kill pathogens in many types of liquids. Pasteur's process involved heating wine to 55°Cb and holding it at that temperature for several minutes; today, pasteurization is accomplished by heating liquids to 63° to 65°C for 30 minutes or to 73° to 75°C for 15 seconds. It should be noted that pasteurization does not kill all of the microorganisms in liquids—just the pathogens. Page 12 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Pasteur discovered the infectious agents that caused the silkworm diseases that were crippling the silk industry in France. He also discovered how to prevent such diseases. Pasteur made significant contributions to the germ theory of disease—the theory that specific microorganisms cause specific infectious diseases. For example, anthrax is caused by a specific bacterium ( Bacillus anthracis ), whereas tuberculosis is caused by a different bacterium ( Mycobacterium tuberculosis ). Pasteur championed changes in hospital practices to minimize the spread of disease by pathogens. Pasteur developed vaccines to prevent chicken cholera, anthrax, and swine erysipelas (a skin disease). It was the development of these vaccines that made him famous in France. Before the vaccines, these diseases were decimating chickens, sheep, cattle, and pigs in that country—a serious economic problem. Pasteur developed a vaccine to prevent rabies in dogs and successfully used the vaccine to treat human rabies. Historical Note An Ethical Dilemma for Louis Pasteur In July 1885, while he was developing a vaccine that would prevent rabies in dogs, Louis Pasteur faced an ethical decision. A 9-year-old boy, named Joseph Meister, had been bitten 14 times on the legs and hands by a rabid dog. At the time, it was assumed that virtually anyone who was bitten by a rabid animal would die. Meister's mother begged Pasteur to use his vaccine to save her son. Pasteur was a chemist, not a physician, and thus was not authorized to treat humans. Also, his experimental vaccine had never been administered to a human being. Nonetheless, 2 days after the boy had been bitten, Pasteur injected Meister with the vaccine in an attempt to save the boy's life. The boy survived, and Pasteur realized that he had developed a rabies vaccine that could be administered to a person after they had been infected with rabies virus. To honor Pasteur and continue his work, especially in the development of a rabies vaccine, the Pasteur Institute was created in Paris in 1888. It became a clinic for rabies treatment, a research center for infectious diseases, and a teaching center. Many scientists who studied under Pasteur went on to make important discoveries of their own and create a vast international network of Pasteur Institutes. The first of the foreign institutes was founded in Saigon, Vietnam, which today is known as Ho Chi Minh City. One of the directors of that institute was Alexandre Emil Jean Yersin—a former student of Robert Koch and Louis Pasteur—who, in 1894, discovered the bacterium that causes plague. Robert Koch (1843–1910) Robert Koch (Fig. 1-9), a German physician, made numerous contributions to the science of microbiology. Some of them are listed here: Figure 1-8. Pasteur in his laboratory. A 1925 wood engraving by Timothy Cole. (Zigrosser C. Medicine and the Artist [Ars Medica]. New York: Dover Publications, Inc., 1970. By permission of the Philadelphia Museum of Art.) P.10 Page 13 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...Koch made many significant contributions to the germ theory of disease. For example, he proved that the anthrax bacillus ( Bacillus anthracis ), which had been discovered earlier by other scientists, was truly the cause of anthrax. He accomplished this using a series of scientific steps which he and his colleagues had developed; these steps later became known as Koch's Postulates (described later in this chapter). Koch discovered that Bacillus anthracis produces spores, capable of resisting adverse conditions. Koch developed methods of fixing, staining, and photographing bacteria. Koch developed methods of cultivating bacteria on solid media. One of Koch's colleagues, R.J. Petri, invented a flat glass dish (now known as a Petri dish ) in which to cultur e bacteria on solid media. It was Frau Hess—the wife of another of Koch's colleagues—who suggested the use of agar (a polysaccharide obtained from seaweed) as a solidifying agent. These methods enabled Koch to obtain pure cultures of bacteria. The term pure culture refers to a condition in which only one type of organism is growing on a solid culture medium or in a liquid culture medium in the laboratory; no other types of organisms are present. Koch discovered the bacterium ( Mycobacterium tuberculosis ) that causes tuberculosis and the bacterium ( Vibrio cholerae ) that causes cholera. Koch's work on tuberculin (a protein derived from M. tuberculosis ) ultimately led to the development of a skin test valuable in diagnosing tuberculosis. Koch's Postulates During the mid- to late-1800s, Robert Koch and his colleagues established an experimental procedure to prove that a specific microorganism is the cause of a specific infectious disease. This scientific procedure, published in 1884, became known as Koch's Postulates (Fig. 1-10). Koch's Postulates (paraphrased): 1. A particular microorganism must be found in all cases of the disease and must not be present in healthy animals or humans. 2. The microorganism must be isolated from the diseased animal or human and grown in pure culture in the laboratory. Page 14 of 20 10/5/2009 http://the pointeedition.lww.com/ pt/re/9780781771955/bookContentPane _frame.htm; jsessi ...