A Brief History of Microbiology PDF

1 A Brief History of Microbiology Clinical Case: A SIMPLE CASE OF TRAVELER’S DIARRHEA? Martin is a nurse in Chicago. Every summer, he spends a few manages to return to Chicago on schedule. A day later, he weeks in Africa volunteering in a rural village in Za...

1 A Brief History of Microbiology Clinical Case: A SIMPLE CASE OF TRAVELER’S DIARRHEA? Martin is a nurse in Chicago. Every summer, he spends a few manages to return to Chicago on schedule. A day later, he weeks in Africa volunteering in a rural village in Zambia. The begins experiencing diarrhea. At first, he brushes it off as village has no sanitation system and gets its water from a “traveler’s diarrhea,” which can be caused by a change in nearby shallow well. Over time, Martin has gained the diet and usually goes away quickly. However, over the following villagers’ trust and demonstrated handwashing technique, days, Martin’s symptoms worsen. The diarrhea is much safer food preparation, and other ways to prevent infectious more severe than anything Martin has experienced before; it is disease. Water purification is especially a challenge: milky, with flecks of mucus, and frightening-looking. Martin boiling water requires fuel that isn’t always available, and also develops nausea, vomiting, and muscle cramps. chemicals that make water safer to drink are often in short He drinks massive amounts of water and tries over-the-counter supply. diarrhea medicine, but nothing he does relieves the symptoms. During the last week of Martin’s most recent Africa trip, Is Martin suffering from a simple case of “traveler’s torrential rains hit the country, causing flash floods and diarrhea”? Or is something more serious going on? Turn extensive damage to the village. Despite the conditions, Martin to page 22 to find out. Take the pre-test for this chapter online. Visit the Study Area at www.masteringmicrobiology.com. 2 CHAPTER 1 A Brief History of Microbiology Science is the study of nature that proceeds by posing questions about observations. Why are there seasons? What is the func- tion of the nodules at the base of this plant? Why does this bread taste sour? What does plaque from between teeth look like when magnified? Why are so many crows dying this win- ter? What causes new diseases? Many early written records show that people have always asked questions like these. For example, the Greek physician Hippocrates (ca. 460–ca. 377 B.C.) wondered whether there is a link between environment and disease, and the Greek historian Thucydides (ca. 460–ca. 404 B.C.) questioned why he and other survivors of the plague could have intimate contact with vic- tims and not fall ill again. For many centuries, the answers to these and other fundamental questions about the nature of life remained largely unanswered. But about 350 years ago, the in- vention of the microscope began to provide some clues. In this chapter we’ll see how one man’s determination to answer a fundamental question about the nature of life—What does life really look like?—led to the birth of a new science called ➤ Figure 1.1 Antoni van Leeuwenhoek. Leeuwenhoek reported microbiology. We’ll then see how the search for answers to other the existence of protozoa in 1674 and of bacteria in 1676. Why did questions, such as those concerning spontaneous generation, the Leeuwenhoek discover protozoa before bacteria? Figure 1.1 Protozoa are generally larger than bacteria. reason fermentation occurs, and the cause of disease, prompted advances in this new science. Finally, we’ll look briefly at some of the key questions microbiologists are asking today. Making and looking through his simple microscopes, most really no more than magnifying glasses, became the over- The Early Years of Microbiology whelming passion of his life. His enthusiasm and dedication are evident from the fact that he sometimes personally ex- The early years of microbiology brought the first observations tracted the metal for his microscope from ore. Further, he often of microbial life and the initial efforts to organize them into log- ical classifications. Lens Specimen holder What Does Life Really Look Like? Learning Objectives ✓ Describe the world-changing scientific contributions of Leeuwenhoek. ✓ Define microbes in the words of Leeuwenhoek and as we know them today. A few people have changed the world of science forever. We’ve all heard of Galileo, Newton, and Einstein, but the list also in- cludes Antoni van Leeuwenhoek (lā¿vĕn-huk; 1632–1723), a Dutch tailor, merchant, and lens grinder, and the man who first discovered the bacterial world (Figure 1.1). Leeuwenhoek was born in Delft, the Netherlands, and lived most of his 90 years in the city of his birth. What set Leeuwenhoek apart from most other men of his generation was an insatiable curiosity coupled with an almost stubborn desire to do everything for himself. His journey to fame began simply enough, when as a tailor he needed to examine the quality of cloth. Rather than merely buying one of the magnifying lenses ➤ already available, he learned to make glass lenses of his own Figure 1.2 Reproduction of Leeuwenhoek’s microscope. (Figure 1.2). Soon he began asking, “What does it really look This simple device is little more than a magnifying glass with screws for like?” of everything in his world: the stinger of a bee, the brain manipulating the specimen; yet with it, Leeuwenhoek changed the way we see our world. The lens, which is convex on both sides, is about the of a fly, the leg of a louse, a drop of blood, flakes of his own size of a pinhead. The object to be viewed was mounted either directly skin. To find answers, he spent hours examining, reexamining, on the specimen holder or inside a small glass tube, which was then and recording every detail of each object he observed. mounted on the specimen holder.  CHAPTER 1 A Brief History of Microbiology 3 made a new microscope for each specimen, which remained mounted so that he could view it again and again. Then one day, he turned a lens onto a drop of water. We don’t know what he expected to see, but certainly he saw more than he had antici- pated. As he reported to the Royal Society of London1 in 1674, he was surprised and delighted by some green streaks, spirally wound serpent-wise, and or- derly arranged.... Among these there were, besides, very many little animalcules, some were round, while others a bit bigger consisted of an oval. On these last, I saw two lit- tle legs near the head, and two little fins at the hind most end of the body.... And the motion of most of these animalcules in the water was so swift, and so various, upwards, downwards, and round about, that ‘twas won- derful to see. Leeuwenhoek had discovered a previously unknown microbial world, which today we know to be populated with tiny ani- LM 50 μm mals, fungi, algae, and single-celled protozoa (Figure 1.3). In a later report to the Royal Society, he noted that ➤ Figure 1.3 The microbial world. Leeuwenhoek reported seeing a scene very much like this, full of numerous, fantastic, cavorting creatures. the number of these animals in the plaque of a man’s teeth, are so many that I believe they exceed the number of men in a kingdom.... I found too many living animals imal kingdom or the plant kingdom. Today, biologists still use therein, that I guess there might have been in a quantity this basic system, but they have modified Linnaeus’s scheme by of matter no bigger than the 1/100 part of a [grain of] adding categories that more realistically reflect the relation- sand. ships among organisms. For example, scientists no longer clas- sify yeasts, molds, and mushrooms as plants, but instead as From the figure accompanying this report and the precise de- fungi. We examine taxonomic schemes in more detail in scription of the size of these organisms from between his teeth, Chapter 4. we know that Leeuwenhoek was reporting the existence of The microorganisms that Leeuwenhoek described can be bacteria. By the end of the 19th century, Leeuwenhoek’s grouped into six basic categories: bacteria, archaea, fungi, pro- “beasties,” as he sometimes dubbed them, were called tozoa, algae, and small multicellular animals. The only type of microorganisms, and today we also know them as microbes. microbes not described by Leeuwenhoek are viruses,2 which are Both terms include all organisms that are too small to be seen too small to be seen without an electron microscope. We briefly without a microscope. consider organisms in the first five categories in the following Because of the quality of his microscopes, his profound ob- sections. servational skills, his detailed reports over a 50-year period, and his report of the discovery of many types of microorgan- Bacteria and Archaea isms, Antoni van Leeuwenhoek was elected to the Royal Society in 1680. He and Isaac Newton were probably the most Bacteria and archaea are prokaryotic;3 meaning that they lack famous scientists of their time. nuclei; that is, their genes are not surrounded by a membrane. Bacterial cell walls are composed of a polysaccharide called peptidoglycan. (Some bacteria, however, lack cell walls.) The cell How Can Microbes Be Classified? walls of archaea lack peptidoglycan and instead are composed Learning Objectives of other chemicals. Members of both groups reproduce asexu- ally. Chapters 3, 4, and 11 examine other differences between ✓ List six groups of microorganisms. bacteria and archaea, and Chapters 19–24 discuss pathogenic ✓ Explain why protozoa, algae, and nonmicrobial parasitic (disease-causing) bacteria. worms are studied in microbiology. ✓ Differentiate prokaryotic from eukaryotic organisms. 1The Royal Society of London for the Promotion of Natural Knowledge, granted a royal Shortly after Leeuwenhoek made his discoveries, the Swedish charter in 1662, is one of the older and more prestigious scientific groups in Europe. 2Technically, viruses are not “organisms,” because they neither replicate themselves nor botanist Carolus Linnaeus (1707–1778) developed a taxonomic carry on the chemical reactions of living things. See Chapter 3 for a fuller discussion of system—a system for naming plants and animals and grouping this issue. 3From Greek pro, meaning before, and karyon, meaning kernel (which in this case similar organisms together. For instance, Linnaeus and other refers to the nucleus of a cell). scientists of the period grouped all organisms into either the an- 4 CHAPTER 1 A Brief History of Microbiology Prokaryotic Nucleus of Hyphae Spores Budding cells bacterial cells eukaryotic cheek cell LM SEM LM 20 μm (a) 10 μm (b) 5 μm ➤ ➤ Figure 1.4 Cells of the bacterium Streptococcus (dark blue) Figure 1.5 Fungi. (a) The mold Penicillium chrysogenum, which and two human cheek cells. Notice the size difference. produces penicillin, has long filamentous hyphae that intertwine to form its body. It reproduces by spores. (b) The yeast Saccharomyces cerevisiae. Yeasts are round to oval and typically reproduce by budding. Most archaea and bacteria are much smaller than eukary- otic cells (Figure 1.4). They live singly or in pairs, chains, or clusters in almost every habitat containing sufficient moisture. cell grows off the mother cell. Some yeasts also produce sexual Archaea are often found in extreme environments, such as the spores. An example of a useful yeast is Saccharomyces cerevisiae highly saline Mono Lake in California, acidic hot springs in Yel- (sak-ă-rō-mı̄¿sēz se-ri-vis¿ē-ı̄; Figure 1.5b), which causes bread lowstone National Park, and oxygen-depleted mud at the bot- to rise and produces alcohol from sugar (see Beneficial Mi- tom of swamps. No archaea are known to cause disease. crobes: Bread, Wine, and Beer! on p. 7). Candida albicans Though bacteria may have a poor reputation in our world, (kan¿did-ă al¿bi-kanz) is a yeast that causes most cases of yeast the great majority do not cause disease in animals, humans, or infections in women. crops. Indeed, bacteria are beneficial to us in many ways. For Fungi and their significance in the environment, in food example, bacteria (and fungi) degrade dead plants and animals production, and as agents of human disease are discussed in to release phosphorus, sulfur, nitrogen, and carbon back into Chapters 12 and 19–24. the air, soil, and water to be used by new generations of organ- isms. Without microbial recyclers, the world would be buried Protozoa under the corpses of uncountable dead organisms. Protozoa are single-celled eukaryotes that are similar to ani- mals in their nutritional needs and cellular structure. In fact, Fungi protozoa is Greek for “first animals,” though scientists today Fungi (fŭn¿jı̄)4 cells are eukaryotic;5 that is, each of their cells classify them in their own groups rather than as animals. Most contains a nucleus composed of genetic material surrounded by protozoa are capable of locomotion, and one way scientists cat- a distinct membrane. Fungi are different from plants because egorize protozoa is according to their locomotive structures: they obtain their food from other organisms (rather than pseudopodia,6 cilia,7 or flagella.8 Pseudopodia are extensions of a making it for themselves). They differ from animals by having cell that flow in the direction of travel (Figure 1.6a). Cilia are cell walls. numerous, short protrusions of a cell that beat rhythmically to Microscopic fungi include some molds and yeasts. Molds propel the protozoan through its environment (Figure 1.6b). are typically multicellular organisms that grow as long filaments Flagella are also extensions of a cell, but are fewer, longer, that intertwine to make up the body of the mold. Molds repro- and more whiplike than cilia (Figure 1.6c). Some protozoa, such duce by sexual and asexual spores, which are cells that produce as the malaria-causing Plasmodium (plaz-mō¿dē-ŭm), are non- a new individual without fusing with another cell (Figure 1.5a). motile in their mature forms. The cottony growths on cheese, bread, and jams are molds. Penicillium chrysogenum (pen-i-sil¿ē-ŭm krı̄-so¿jĕn-ŭm) is a mold 4 Plural of the Latin fungus, meaning mushroom. 5 that produces penicillin. From Greek eu, meaning true, and karyon, meaning kernel. 6From Greek pseudes, meaning false, and podos, meaning foot. Yeasts are unicellular and typically oval to round. They re- 7Plural of the Latin cilium, meaning eyelid. produce asexually by budding, a process in which a daughter 8Plural of the Latin flagellum, meaning whip.  CHAPTER 1 A Brief History of Microbiology 5 ➤ Figure 1.6 Locomotive structures of protozoa. (a) Pseudopodia Nucleus Pseudopodia are cellular extensions used for locomotion and feeding, as seen in Amoeba proteus. (b) Cilia are short, motile, hairlike extrusions, as seen in Euplotes. (c) Flagella are whiplike extensions that are less numerous and longer than cilia, as seen in Perenema. How do cilia and flagella differ? flagella are long and relatively few in number. Figure 1.6 Cilia are short, numerous, and often cover the cell, whereas Protozoa typically live freely in water, but some live inside animal hosts, where they can cause disease. Most protozoa re- produce asexually, though some are sexual as well. Chapters 12 and 19–24 further examine protozoa. Algae Algae9 are unicellular or multicellular photosynthetic organisms; that is, like plants they make their own food from carbon diox- ide and water using energy from sunlight. They differ from (a) LM 200 μm plants in the relative simplicity of their reproductive structures. Algae are categorized on the basis of their pigmentation and the composition of their cell walls. Cilia Large algae, commonly called seaweeds and kelps, are common in the world’s oceans. Chemicals from their gelatinous cell walls are used as thickeners and emulsifiers in many food and cosmetic products, as well as in microbiological laboratory media. Unicellular algae (Figure 1.7) are common in freshwater ponds, streams, and lakes, and in the oceans as well. They are the major food of small aquatic and marine animals and pro- vide most of the world’s oxygen as a by-product of photosyn- thesis. The glasslike cell walls of diatoms provide grit for many polishing compounds. Chapter 12 discusses other aspects of the biology of algae. CRITICAL THINKING A few bacteria produce disease because they derive nutrition from human cells and produce toxic wastes. Algae do not cause disease. (b) LM 10 μm Why not? Flagellum Other Organisms of Importance to Microbiologists Microbiologists also study parasitic worms, which range in size from microscopic forms (Figure 1.8) to adult tapeworms over 7 meters (approximately 23 feet) in length. Even though most of these worms are not microscopic as adults, many of them cause diseases that were studied by early microbiologists. Further, laboratory technicians diagnose infections of parasitic worms by finding microscopic eggs and immature stages in blood, fecal, urine, and lymph specimens. Chapters 21 and 23 discuss parasitic worms. The only type of microbe that remained hidden from Leeuwenhoek and other early microbiologists was viruses, 9Plural of the Latin alga, meaning seaweed. LM (c) 20 μm 6 CHAPTER 1 A Brief History of Microbiology (a) LM (b) LM 10 μm 10 μm ➤ Figure 1.7 Algae. (a) Spirogyra. These microscopic algae grow as chains of cells containing helical photosynthetic structures. (b) Diatoms. These beautiful algae have glasslike cell walls. which are much smaller than the smallest prokaryote and are microscopes, he never trained an apprentice, and he never sold not visible by light microscopy (Figure 1.9). Viruses could not or gave away a microscope. In fact, he never let anyone—not his be seen until the electron microscope was invented in 1932. All family or such distinguished visitors as the czar of Russia—so viruses are acellular (not composed of cells) obligatory para- much as peek through his very best instruments. When sites composed of small amounts of genetic material (either Leeuwenhoek died, the secret of creating superior microscopes DNA or RNA) surrounded by a protein coat. Chapter 13 exam- ines the general characteristics of viruses, and Chapters 18–24 discuss specific viral pathogens. Leeuwenhoek first reported the existence of most types of Virus microorganisms in the late 1600s, but microbiology did not develop significantly as a field of study for almost two centuries. There were a number of reasons for this delay. First, Leeuwenhoek was a suspicious and secretive man. Though he built over 400 Bacterium Red blood cell Viruses assembling inside cell TEM 75 nm ➤ Figure 1.9 A colorized electron microscope image of viruses infecting a bacterium. Viruses, which are acellular obligatory parasites, LM are too small to be seen with a light microscope. Notice how small the 30 μm viruses are compared to the bacterium. ➤ Figure 1.8 An immature stage of a parasitic worm in blood.  CHAPTER 1 A Brief History of Microbiology 7 was lost. It took almost 100 years for scientists to make micro- What causes disease? scopes of equivalent quality. How can we prevent infection and disease? Another reason that microbiology was slow to develop as a Competition among scientists who were striving to be the first science is that scientists in the 1700s considered microbes to be to answer these questions drove exploration and discovery in curiosities of nature and insignificant to human affairs. But in microbiology during the late 1800s and early 1900s. These sci- the late 1800s, scientists began to adopt a new philosophy, one entists’ discoveries and the fields of study they initiated con- that demanded experimental proof rather than mere acceptance tinue to shape the course of microbiological research today. of traditional knowledge. This fresh philosophical foundation, In the next sections we consider these questions and how accompanied by improved microscopes, new laboratory tech- the great scientists accumulated the experimental evidence that niques, and a drive to answer a series of pivotal questions, pro- answered them. pelled microbiology to the forefront as a scientific discipline. Does Microbial Life Spontaneously The Golden Age of Microbiology Generate? Learning Objective Learning Objectives ✓ List and answer four questions that propelled research in what ✓ Identify the scientists who argued in favor of spontaneous is called the “Golden Age of Microbiology.” generation. For about 50 years, during what is sometimes called the ✓ Compare and contrast the investigations of Redi, Needham, “Golden Age of Microbiology,” scientists and the blossoming Spallanzani, and Pasteur concerning spontaneous generation. field of microbiology were driven by the search for answers to ✓ List four steps in the scientific method of investigation. the following four questions: A dry lakebed has lain under the relentless North African Is spontaneous generation of microbial life possible? desert sun for eight long months. The cracks in the baked, What causes fermentation? parched mud are wider than a man’s hand. There is no sign of BENEFICIAL MICROBES BREAD, WINE, AND BEER! Microorganisms play is naturally found on grapes, which can begin to ferment while important roles in people’s still on the vine. Historians hypothesize that early bakers may lives; for example, have exposed bread dough to circulating air, hoping that the pathogens have invisible and inexplicable “fermentation principle” would undeniably altered the inoculate the bread. Another hypothesis is that bakers learned course of history. However, to add small amounts of beer or wine to the bread, intentionally what may be the most inoculating the dough with yeast. Of course, all those years important microbiological before Leeuwenhoek and Pasteur, no one knew that the event—one that has had fermenting ingredient of wine was a living organism. a greater impact upon Besides its role in baking and in making alcoholic beverages, culture and society than that of any disease or epidemic—was S. cerevisiae is an important tool for the study of cells. Scientists the domestication of the yeast used by bakers and brewers. Its use yeast to delve into the mysteries of cellular function, name, Saccharomyces cerevisiae, means “sugar fungus [that organization, and genetics, making Saccharomyces the most makes] beer.” intensely studied eukaryote. In fact, molecular biologists The earliest record of the use of yeast comes from Persia published the complete sequence of the genes of S. cerevisiae (modern Iran), where archeologists have found the remains of in 1996—a first for any eukaryotic cell. grapes and wine preservatives in pottery vessels more than Today, scientists are working toward using S. cerevisiae 7000 years old. Brewing of beer likely started even earlier, its in novel ways. For example, some nutritionists and beginnings undocumented. The earliest examples of leavened gastroenterologists are examining the use of Saccharomyces as bread are from Egypt and show that bread-making was routine a probiotic; that is, a microorganism intentionally taken to ward about 6000 years ago. Before that time, bread was unleavened off disease and promote good health. Research suggests that and flat. the yeast helps treat diarrhea and colitis and may help prevent It is likely that making wine and brewing beer occurred these and other gastrointestinal diseases. earlier than the use of leavened bread because Saccharomyces 8 CHAPTER 1 A Brief History of Microbiology duction, through sexual reproduction, or from nonliving matter. The appearance of shrimp and toads in the mud of what so re- cently was a dry lakebed was seen as an example of the third process, which came to be known as abiogenesis,10 or spontaneous generation. The theory of spontaneous generation as promul- gated by Aristotle (384–322 B.C.) was widely accepted for over 2000 years because it seemed to explain a variety of commonly observed phenomena, such as the appearance of maggots on spoiling meat. However, the validity of the theory came under challenge in the 17th century. Flask unsealed Flask sealed Flask covered Redi’s Experiments with gauze In the late 1600s, the Italian physician Francesco Redi ➤ Figure 1.10 Redi’s experiments. When the flask remained (1626–1697) demonstrated by a series of experiments that when unsealed, maggots covered the meat within a few days. When the flask decaying meat was kept isolated from flies, maggots never de- was sealed, flies were kept away and no maggots appeared on the meat. When the flask opening was covered with gauze, flies were kept away and veloped, whereas meat exposed to flies was soon infested no maggots appeared on the meat, although a few maggots appeared (Figure 1.10). As a result of experiments such as these, scientists on top of the gauze. began to doubt Aristotle’s theory and adopt the view that ani- mals come only from other animals. life anywhere in the scorched terrain. With the abruptness char- Needham’s Experiments acteristic of desert storms, rain falls in a torrent, and a raging The debate over spontaneous generation was rekindled when flood of roiling water and mud crashes down the dry Leeuwenhoek discovered microbes and showed that they streambed and fills the lake. Within hours, what had been a life- appeared after a few days in freshly collected rainwater. less, dry mudflat becomes a pool of water teeming with billions of shrimp; by the next day it is home to hundreds of toads. 10 Where did these animals come from? From Greek a, meaning not; bios, meaning life; and genein, meaning to produce. Many philosophers and scientists of past ages thought that living things arose via three processes: through asexual repro- HIGHLIGHT “THE NEW NORMAL”: THE CHALLENGE OF EMERGING AND REEMERGING DISEASES Severe acute respiratory syndrome Other near-vanquished pathogens such (SARS). Monkeypox. West Nile as smallpox or anthrax may become encephalitis. These and diseases like potential weapons in bioterrorist them are emerging diseases—ones attacks. that appear in a population for the first How do emerging and reemerging time. Among them are H1N1 influenza diseases arise? Some are introduced to (“swine flu”); Nipah encephalitis, a humans as we move into remote jungles ➤ highly fatal disease carried by pigs; and and contact infected animals; some Workers dumping poultry suspected of harboring avian influenza virus. mosquito-borne chikungunya, which are carried by insects whose range is causes severe joint pain and sometimes spreading as climate changes; some take arise when previously treatable microbes death. Indeed, unfamiliar diseases have advantage of the AIDS crisis, infecting develop resistance to our antibiotics. become “the new normal” for health immunocompromised patients; some However they arise, scientists are care workers, according to the Centers previously harmless microbes acquire monitoring emerging and reemerging for Disease Control and Prevention. new genes that allow them to be diseases that may develop into the next Meanwhile, diseases once thought infective and cause disease; some generation of high-profile infectious to be near eradication, such as polio, emerging pathogens spread with the diseases. Throughout this textbook, you mumps, and tuberculosis, have speed of jet planes carrying infected will encounter many boxed discussions of reemerged in troubling outbreaks. people around the globe; and still others such emerging and reemerging diseases.  CHAPTER 1 A Brief History of Microbiology 9 Though scientists agreed that larger animals could not arise spontaneously, they disagreed about Leeuwenhoek’s “wee ani- malcules”; surely they did not have parents, did they? They must arise spontaneously. The proponents of spontaneous generation pointed to the careful demonstrations of British investigator John T. Needham (1713–1781). He boiled beef gravy and infusions11 of plant ma- terial in vials, which he then tightly sealed with corks. Some days later, Needham observed that the vials were cloudy, and examination revealed an abundance of “microscopical [sic] ani- mals of most dimensions.” As he explained it, there must be a “life force” that causes inanimate matter to spontaneously come to life, because he had heated the vials sufficiently to kill everything. Needham’s experiments so impressed the Royal Society that they elected him a member. Spallanzani’s Experiments ➤ Figure 1.11 Louis Pasteur. Often called the Father of Then, in 1799, the Italian scientist Lazzaro Spallanzani Microbiology, he disproved spontaneous generation. In this depiction, (1729–1799) reported results that contradicted Needham’s find- Pasteur examines some bacterial cultures. ings. Spallanzani boiled infusions for almost an hour and sealed the vials by melting their slender necks closed. His infu- sions remained clear, unless he broke the seal and exposed the complained about his long hours in the laboratory, he replied, infusion to air, after which they became cloudy with microor- “I will lead you to fame.” ganisms. He concluded three things: Pasteur’s determination and hard work are apparent in his Needham had either failed to heat his vials sufficiently investigations of spontaneous generation. Like Spallanzani, he to kill all microbes, or he had not sealed them tightly boiled infusions long enough to kill everything. But instead of enough. sealing the flasks, he bent their necks into an S-shape, which al- lowed air to enter while preventing the introduction of dust Microorganisms exist in the air and can contaminate and microbes into the broth (Figure 1.12). experiments. Crowded for space and lacking funds, he improvised an in- Spontaneous generation of microorganisms does not occur; cubator in the opening under a staircase. Day after day he all living things arise from other living things. crawled on hands and knees into this incommodious space and Although Spallanzani’s experiments would appear to have examined his flasks for the cloudiness that would indicate the settled the controversy once and for all, it proved difficult to presence of living organisms. In 1861, he reported that his dethrone a theory that had held sway for 2000 years, especially “swan-necked flasks” remained free of microbes even 18 months when so notable a man as Aristotle had propounded it. One of later. Because the flasks contained all the nutrients (including the criticisms of Spallanzani’s work was that his sealed vials air) known to be required by living things, he concluded, did not allow enough air for organisms to thrive; another objec- “Never will spontaneous generation recover from the mortal tion was that his prolonged heating destroyed the “life force.” blow of this simple experiment.” The debate continued until the French chemist Louis Pasteur Pasteur followed this experiment with demonstrations that (Figure 1.11) conducted experiments that finally laid the theory microbes in the air were the “parents” of Needham’s microor- of spontaneous generation to rest. ganisms. He broke the necks off some flasks, exposing the liquid in them directly to the air, and he carefully tilted others so that Pasteur’s Experiments the liquid touched the dust that had accumulated in their necks. The next day, all of these flasks were cloudy with microbes. He Louis Pasteur (1822–1895) was an indefatigable worker who concluded that the microbes in the liquid were the progeny of pushed himself as hard as he pushed others. As he wrote his microbes that had been on the dust particles in the air. sisters, “To will is a great thing dear sisters, for Action and Work usually follow Will, and almost always Work is accompa- The Scientific Method nied by Success. These three things, Work, Will, Success, fill human existence. Will opens the door to success both brilliant The debate over spontaneous generation led in part to the devel- and happy; Work passes these doors, and at the end of the opment of a generalized scientific method by which questions journey Success comes to crown one’s efforts.” When his wife are answered through observations of the outcomes of carefully controlled experiments, instead of by conjecture or according to 11Infusions are broths made by steeping plant or animal material in water. the opinions of any authority figure. The scientific method, which provides a framework for conducting an investigation 10 CHAPTER 1 A Brief History of Microbiology Steam escapes Dust from from open end Air moves in air settles of flask. and out of flask. in bend. Months Infusion Infusion sits; Infusion remains is heated. no microbes appear. sterile indefinitely. ➤ Figure 1.12 Pasteur’s experiments with “swan-necked flasks.” As long as the flask remained upright, no microbial growth appeared in the infusion. rather than a rigid set of specific “rules,” consists of four basic the other groups in the experiment, except for the one variable steps (Figure 1.13): that the experiment is designed to test. In Pasteur’s experi- 1 A group of observations leads a scientist to ask a question ments on spontaneous generation, for example, his “control about some phenomenon. flasks” contained a sterile infusion composed of all the nutri- ents living things need, as well as air made available through 2 The scientist generates a hypothesis—that is, a potential an- the flasks’ “swan necks.” His “experimental flasks” for testing swer to the question. his hypothesis—that microbes would reach (and subsequently 3 The scientist designs and conducts an experiment to test grow in) the infusion through contact with dust particles—were the hypothesis. exposed to exactly the same conditions, plus contact with the 4 Based on the observed results of the experiment, the scien- dust in the bend in the neck. Because exposure to the dust was tist either accepts, rejects, or modifies the hypothesis. the only difference between the control and experimental As shown in Figure 1.13, the scientist then returns to earlier steps groups, Pasteur was able to conclude that the microbes growing in the method, either modifying hypotheses and then testing in the infusion arrived on the dust particles. them, or repeatedly testing accepted hypotheses, until the evi- dence for a hypothesis is convincing. Accepted hypotheses that What Causes Fermentation? explain many observations and are repeatedly verified by nu- merous scientists over many years are called theories or laws. Learning Objectives Note that for the scientific community to accept experi- ✓ Discuss the significance of Pasteur’s fermentation experiments ments (and their results) as valid, they must include appropri- to our world today. ate control groups—groups that are treated exactly the same as ➤ Figure 1.13 Observations The scientific method, which forms a framework for scientific 1 research. Question Repeat Experimental Accept Theory or law data support hypothesis 2 hypothesis 3 Experiment, Hypothesis including Observations 4 Reject control groups Experimental hypothesis data do not support Modified hypothesis Modify hypothesis hypothesis  CHAPTER 1 A Brief History of Microbiology 11 ✓ Explain why Pasteur may be considered the Father of the juice’s basic qualities, so that it could then be inoculated Microbiology. with yeast to ensure that alcohol fermentation occurred. Pas- ✓ Identify the scientist whose experiments led to the field of teur thus began the field of industrial microbiology (or biochemistry and the study of metabolism. biotechnology) in which microbes are intentionally used to manufacture products (Table 1.1 on p. 13; see also Chapter 25). The controversy over spontaneous generation was largely a Today pasteurization is used routinely on milk to eliminate philosophical exercise among men who conducted research to pathogens that cause such diseases as bovine tuberculosis and gain basic scientific knowledge. They had no practical goals in brucellosis; it is also used to eliminate pathogens in juices and mind—except, perhaps, personal aggrandizement in the form other beverages. of financial support, honor, and prestige. However, the second These are just a few of the many experiments Pasteur con- question that moved microbial studies forward in the 1800s had ducted with microbes. Although a few of Pasteur’s successes tremendous practical applications. can be attributed to the superior microscopes available in the Our story resumes in 19th-century France, where spoiled, late 1800s, his genius is clearly evident in his carefully designed acidic wine was threatening the livelihood of many grape and straightforward experiments. Because of his many, varied, growers. The initial question was, “Why is the wine spoiled?” and significant accomplishments in working with microbes, but this led to a more fundamental question, “What causes the Pasteur may be considered the Father of Microbiology. fermentation of grape juice into wine?” These questions were so important to vintners that they funded research concerning fer- Buchner’s Experiments mentation, hoping scientists could develop methods to pro- mote the production of alcohol and prevent spoilage by acid Studies on fermentation began with the idea that fermentation during fermentation. reactions were strictly chemical and did not involve living or- ganisms. This idea was supplanted by Pasteur’s work showing Pasteur’s Experiments that fermentation proceeded only when living cells were present and that different types of microorganisms growing under var- Scientists of the 1800s used the word fermentation to mean not ied conditions produced different end products. only the formation of alcohol from sugar, but also other chemi- In 1897, the German scientist Eduard Buchner (1860–1917) cal reactions such as the formation of lactic acid, the putrefac- resurrected the chemical explanation by showing that fermenta- tion of meat, and the decomposition of waste. Many scientists tion does not require living cells. Buchner’s experiments demon- asserted that air caused fermentation reactions; others insisted strated the presence of enzymes, which are cell-produced proteins that living organisms were responsible. that promote chemical reactions. Buchner’s work began the field The debate over the cause of fermentation reactions was of biochemistry and the study of metabolism, a term that refers linked to the debate over spontaneous generation. Some scien- to the sum of all chemical reactions within an organism. tists proposed that the yeasts observed in fermenting juices were nonliving globules of chemicals and gases. Others thought that yeasts were alive and were spontaneously gener- CRITICAL THINKING ated during fermentation. Still others asserted that yeasts not How might the debate over spontaneous generation have been only were living organisms, but also caused fermentation. different if Buchner had conducted his experiments in 1857 instead Pasteur conducted a series of careful observations and ex- of 1897? periments that answered the question, “What causes fermenta- tion?” First, he observed yeast cells growing and budding in grape juice and conducted experiments showing that they arise What Causes Disease? only from other yeast cells. Then, by sealing some sterile flasks containing grape juice and yeast, and by leaving others open Learning Objectives to the air, he demonstrated that yeast could grow with or with- ✓ List at least seven contributions made by Koch to the field of out oxygen; that is, he discovered that yeasts are facultative microbiology. anaerobes12—organisms that can live with or without oxygen. ✓ List the four steps that must be taken to prove the cause of an Finally, by introducing bacteria and yeast cells into different infectious disease. flasks of sterile grape juice, he proved that bacteria ferment ✓ Describe the contribution of Gram to the field of grape juice to produce acids and that yeast cells ferment grape microbiology. juice to produce alcohol (Figure 1.14). Pasteur’s discovery that anaerobic bacteria fermented grape You are a physician in London, and it is August 1854. It is past juice into acids suggested a method for preventing the spoilage midnight, and you have been visiting patients since before of wine. His name became a household word when he devel- dawn. As you enter the room of your next patient, you observe oped pasteurization, a process of heating the grape juice just with frustration and despair that this case is like hundreds of enough to kill most contaminating bacteria without changing others you and your colleagues have attended in the neighbor- hood over the past month. A five-year-old boy with a vacant stare lies in bed listlessly. 12From Greek an, meaning not; aer, meaning air (i.e., oxygen); and bios, meaning life. As you watch, he is suddenly gripped by severe abdominal 12 CHAPTER 1 A Brief History of Microbiology Observation: Fermenting Microscopic analysis grape juice shows juice contains yeasts and bacteria. Hypothesis Experiment Observation Conclusion Day 1: Flasks of grape juice Day 2 are heated sufficiently to kill all microbes. I. Spontaneous No fermentation; Reject fermentation occurs. Flask is juice remains hypothesis I. sealed. free of microbes. II. Air ferments No fermentation; Reject grape juice. Flask remains juice remains hypothesis II. open to air free of microbes. via curved neck. III. Bacteria ferment Bacteria reproduce; Modify hypothesis III; grape juice Juice in flask is acids are produced. bacteria ferment into alcohol. inoculated with grape juice into acids. bacteria and sealed. IV. Yeasts ferment Yeasts reproduce; Accept hypothesis IV; grape juice Juice in flask is alcohol is produced. yeasts ferment grape into alcohol. inoculated with juice into alcohol. yeast and sealed. ➤ Figure 1.14 How Pasteur applied the scientific method in investigating the nature of fermentation. After observing that fermenting grape juice contained both yeasts and bacteria, Pasteur hypothesized that these organisms cause fermentation. Upon eliminating the possibility that fermentation could occur spontaneously or be caused by air (hypotheses 1 and 2), he concluded that fermentation requires the presence of living cells. The results of additional experiments (those testing hypotheses 3 and 4) indicated that bacteria ferment grape juice to produce acids and that yeasts ferment grape juice to produce alcohol. Which of Pasteur’s flasks was the control? Figure 1.14 The sealed flask that remained free of microorganisms served as the control. cramps, and his gastrointestinal tract empties in an explosion of The third question that propelled the advance of microbiol- watery diarrhea. The voided fluid is clear, colorless, odorless, ogy concerned disease, defined generally as any abnormal con- and streaked with thin flecks of white mucus, reminiscent of dition in the body. Prior to the 1800s, disease was attributed to water poured off a pot of cooking rice. His anxious mother various factors, including evil spirits, astrological signs, imbal- changes his bedclothes as his father gives him a sip of water, ances in body fluids, and foul vapors. Although the Italian but it is of little use. With a heavy heart you confirm the par- philosopher Girolamo Fracastoro (1478–1553) conjectured as ents’ fear—their child has cholera, and there is nothing you can early as 1546 that “germs13 of contagion” cause disease, the idea do. He will likely die before morning. As you despondently that germs might be invisible living organisms awaited turn to go, the question that has haunted you for two months is Leeuwenhoek’s investigations 130 years later. foremost in your mind: What causes such a disease? 13From Latin germen, meaning sprout.  CHAPTER 1 A Brief History of Microbiology 13 1.1 Some Industrial Uses TABLE of Microbes Product or Process Contribution of Microorganism Foods and Beverages Cheese Flavoring and ripening produced by bacteria and fungi; flavors dependent on the source of milk and the type of microorganism Alcoholic beverages Alcohol produced by bacteria or yeast by fermentation of sugars in fruit juice or grain Soy sauce Produced by fungal fermentation of soybeans Vinegar Produced by bacterial fermentation of sugar Yogurt Produced by bacteria growing in ➤ Figure 1.15 Robert Koch. Koch was instrumental in modifying the skim milk scientific method to prove that a given pathogen caused a specific disease. Sour cream Produced by bacteria growing in cream Artificial sweetener Amino acids synthesized by bacteria from sugar Koch’s Experiments Bread Rising of dough produced by action of yeast; sourdough results from Koch was a country doctor in Germany when he began a race bacteria-produced acids with Pasteur to discover the cause of anthrax, which is a poten- Other Products tially fatal disease, primarily of animals, in which toxins pro- duce ulceration of the skin. Anthrax caused untold financial Antibiotics Produced by bacteria and fungi losses to farmers and ranchers in the 1800s, and the disease can Human growth Produced by genetically engineered be spread to humans. hormone, human bacteria insulin Koch carefully examined the blood of infected animals, and in every case he identified a rod-shaped bacterium17 that formed Laundry enzymes Isolated from bacteria chains. He observed the formation of resting stages (endospores) Vitamins Isolated from bacteria within the bacterial cells and showed that the endospores al- Diatomaceous earth Composed of cell walls of ways produced anthrax when they were injected into mice. This (used in polishes and microscopic algae buffing compounds) was the first time that a bacterium was proven to cause a dis- ease. As a result of his successful work on anthrax, Koch was Pest control Insect pests killed or inhibited by chemicals bacterial pathogens able to move to Berlin and was given facilities and funding to Drain opener Protein-digesting and fat-digesting continue his research. enzymes produced by bacteria Heartened by his success, Koch turned his attention to other diseases. He had been fortunate when he chose anthrax for his initial investigations, because anthrax bacteria are quite large and easily identified with the microscopes of that time. Pasteur’s discovery that bacteria are responsible for spoil- However, most bacteria are very small, and different types ex- ing wine led naturally to his hypothesis in 1857 that microor- hibit few or no visible differences. Koch puzzled how to distin- ganisms are also responsible for diseases. This idea came to be guish among these bacteria. known as the germ theory of disease. Because a particular dis- He solved the problem by taking specimens (for instance, ease is typically accompanied by the same symptoms in all af- blood, pus, or sputum) from disease victims and then smearing fected individuals, early investigators suspected that diseases the specimens onto a solid surface such as a slice of potato or a such as cholera, tuberculosis, and anthrax are each caused by a gelatin medium. He then waited for bacteria and fungi present in specific germ, called a pathogen.14 Today we know that some the specimen to multiply and form distinct colonies (Figure 1.16). diseases are genetic and that allergic reactions and environmen- Koch hypothesized that each colony consisted of the progeny of tal toxins cause others, so the germ theory applies only to a single cell. He then inoculated samples from each colony into infectious15 diseases. laboratory animals to see which caused disease. Koch’s method Just as Pasteur was the chief investigator in disproving spon- taneous generation and determining the cause of fermentation, 14From Greek pathos, meaning disease, and genein, meaning to produce. 15From Latin inficere, meaning to taint (i.e., with a pathogen). so investigations in etiology16 (the study of causation of disease) 16From Greek aitia, meaning cause, and logos, meaning word or study. were dominated by Robert Koch (1843–1910) (Figure 1.15). 17Now known as Bacillus anthracis—Latin for “the rod of anthrax.” 14 CHAPTER 1 A Brief History of Microbiology ➤ Bacterium 6 Bacterium 7 Figure 1.16 Bacterial Bacterium 5 Bacterium 8 colonies on a solid surface (agar). Differences in colony size, Bacterium 4 Bacterium 9 shape, and color indicate the presence of different species. Bacterium 3 Bacterium 10 Such differences allowed Koch to isolate specific types of microbes Bacterium 2 Bacterium 11 that could be tested for their Bacterium 1 Bacterium 12 ability to cause disease. of isolation is a standard technique in microbiological and med- bak-tēr¿ē-ŭm too-ber-kyū-lō¿sis). In 1905 he received the Nobel ical labs to this day, though a gel called agar, derived from red Prize in Physiology or Medicine for this work. seaweed, is used instead of gelatin or potato. In his publications on tuberculosis, Koch elucidated a series Koch and his colleagues are also responsible for many other of steps that must be taken to prove the cause of any infectious advances in laboratory microbiology, including the following: disease. These steps, now known as Koch’s postulates, are one of Simple staining techniques for bacterial cells and flagella his more important contributions to microbiology. His postulates, which we discuss in more detail in Chapter 14, are the following: The first photomicrograph of bacteria 1. The suspected causative agent must be found in every case The first photograph of bacteria in diseased tissue of the disease and be absent from healthy hosts. Techniques for estimating the number of bacteria in a 2. The agent must be isolated and grown outside the host. solution based on the number of colonies that form after inoculation onto a solid surface 3. When the agent is introduced to a healthy, susceptible host, the host must get the disease. The use of steam to sterilize growth media 4. The same agent must be found in the diseased experimen- The use of Petri18 dishes to hold solid growth media tal host. Laboratory techniques such as transferring bacteria between We use the term suspected causative agent because it is merely media using a metal wire that had been heat-sterilized “suspected” until the postulates have been fulfilled, and “agent” in a flame can refer to any fungus, protozoan, bacterium, virus, or other Elucidation of bacteria as distinct species pathogen. There are practical and ethical limits in the applica- tion of Koch’s postulates, but in almost every case they must be CRITICAL THINKING satisfied before the cause of an infectious disease is proven. French microbiologists, led by Pasteur, tried to isolate a single bacterium by diluting liquid media until only a single type of CRITICAL THINKING bacterium could be microscopically observed in a sample of the Why aren’t Koch’s postulates always useful in proving the cause of diluted medium. What advantages does Koch’s method have over a given disease? Consider a variety of diseases, such as cholera, the French method? pneumonia, Alzheimer’s, AIDS, Down syndrome, and lung cancer. Koch’s Postulates During microbiology’s “Golden Age,” other scientists used After discovering the anthrax bacterium, Koch continued to Koch’s postulates, as well as laboratory techniques introduced by search for disease agents. In two pivotal scientific publications Koch and Pasteur, to discover the causes of most protozoan and in 1882 and 1884, he announced that the cause of tuberculosis bacterial diseases, as well as some viral diseases. For example, was a rod-shaped bacterium, Mycobacterium tuberculosis (mı̄¿kō- Charles Laveran (1845–1922) showed that a protozoan is the cause of malaria, and Edwin Klebs (1834–1913) described the bacterium that causes diphtheria. Dmitri Ivanowski (1864–1920) and 18Named for Richard Petri, Koch’s assistant, who invented them in 1887. Martinus Beijerinck (1851–1931) discovered that a certain disease  CHAPTER 1 A Brief History of Microbiology 15 1.2 Other Notable Scientists of the “Golden Age of Microbiology” TABLE and the Agents of Disease They Discovered Scientist Year Disease Agent Albert Neisser 1879 Gonorrhea Neisseria gonorrhoeae (bacterium) Charles Laveran 1880 Malaria Plasmodium species (protozoa) Carl Eberth 1880 Typhoid fever Salmonella enterica serotype Typhi (bacterium) Edwin Klebs 1883 Diphtheria Corynebacterium diphtheriae (bacterium) Theodore Escherich 1884 Traveler’s diarrhea Escherichia coli (bacterium) Bladder infection Albert Fraenkel 1884 Pneumonia Streptococcus pneumoniae (bacterium) David Bruce 1887 Undulant fever (brucellosis) Brucella melitensis (bacterium) Anton Weichselbaum 1887 Meningococcal meningitis Neisseria meningitidis (bacterium) A. A. Gartner 1888 Salmonellosis (form of food Salmonella species (bacterium) poisoning) Shibasaburo Kitasato 1889 Tetanus Clostridium tetani (bacterium) Dmitri Ivanowski and 1892 Tobacco mosaic disease Tobamovirus tobacco mosaic virus Martinus Beijerinck 1898 William Welch and 1892 Gas gangrene Clostridium perfringens (bacterium) George Nuttall Alexandre Yersin and Shibasaburo 1894 Bubonic plague Yersinia pestis (bacterium) Kitasato Kiyoshi Shiga 1898 Shigellosis (a type of severe Shigella dysenteriae (bacterium) diarrhea) Walter Reed 1900 Yellow fever Flavivirus yellow fever virus Robert Forde and Joseph Dutton 1902 African sleeping sickness Trypanosoma brucei gambiense (protozoan) in tobacco plants is caused by a pathogen that passes through fil- Gram-positive Gram-negative ters with such extremely small pores that bacteria cannot pass through. Beijerinck, recognizing that the pathogen was not bacte- rial, called it a filterable virus. Now such pathogens are simply called viruses. As previously noted, viruses couldn’t be seen until electron microscopes were invented in 1932. The American physi- cian Walter Reed (1851–1902) proved in 1900 that viruses can cause such diseases as yellow fever in humans. Chapter 13 deals with virology, and Chapters 18–24 deal with viral diseases. A partial list of scientists and the pathogens they discov- ered is provided in Table 1.2. Gram’s Stain The first of Koch’s postulates demands that the suspected agent be found in every case of a given disease, which presupposes that minute microbes can be seen and identified. However, be- cause most microbes are colorless and difficult to see, scientists began to use dyes to stain them and make them more visible under the microscope. LM Though Koch reported a simple staining technique in 1877, 10 μm the Danish scientist Hans Christian Gram (1853–1938) developed ➤ a more important staining technique in 1884. His procedure, Figure 1.17 Results of Gram staining. Gram-positive cells (in this case Staphylococcus aureus) are purple; Gram-negative cells (in this case which involves the application of a series of dyes, leaves some Escherichia coli) are pink. microbes purple and others pink. We now label the first group of cells as Gram-positive and the second as Gram-negative, and we use the Gram procedure to separate bacteria into these two large groups (Figure 1.17). 16 CHAPTER 1 A Brief History of Microbiology ✓ Name two scientists whose work with vaccines began the field CLINICAL APPLICATIONS of immunology. ✓ Describe the quest for a “magic bullet.” Remedy for Fever or Prescription The last great question that drove microbiological research dur- for Death? ing the “Golden Age” was how to prevent infectious diseases. Though some methods of preventing or limiting disease were In the late 18th century, discovered even before it was understood that microorganisms Philadelphia was one of caused contagious diseases, great advances occurred only after the larger and wealthier Pasteur and Koch showed that life comes from life and that mi- cities in the United States croorganisms can cause diseases. and served as the capital. In the mid-1800s, modern principles of hygiene, such as That changed in 1793. The those involving sewage and water treatment, personal cleanliness, city had an unusually wet and pest control, were not widely practiced. Typically, medical spring, which left behind personnel and health care facilities lacked adequate cleanliness. swamps and stagnant Nosocomial19 infections—infections acquired in a health care set- pools that became ting—were rampant. For example, surgical patients frequently breeding grounds for succumbed to gangrene acquired while under their doctor’s care, mosquitoes. Later, and many women who gave birth in hospitals died from puer- refugees from the slave peral20 fever. Four health care practitioners who were especially revolution in Haiti fled to instrumental in changing the way health care is delivered were Philadelphia, carrying the Semmelweis, Lister, Nightingale, Snow, Jenner, and Ehrlich. yellow fever virus. In late August 1793, a female Aedes aegypti mosquito bit an infected refugee and then bit a Semmelweis and Handwashing healthy Philadelphian. This began a yellow fever epidemic that Ignaz Semmelweis (1818–1865) was a physician on the obstet- killed 10% of the city’s population within three months and ric ward of a teaching hospital in Vienna. In about 1848 he forced another 30% to flee for their lives. Victims suffered from observed that women giving birth in the wing where medical high fever, nausea, skin eruptions, black vomit, and jaundice. students were trained died from puerperal fever at a rate 20 The treatment, however, was worse than the disease: times higher than the mortality rates of either women attended physicians administered potions to purge the victims’ intestines by midwives in an adjoining wing or women who gave birth and drained up to four-fifths of their patients’ blood in the mistaken at home. belief the bloodletting would stem fever. These attempted Though Pasteur had not yet elaborated his germ theory of remedies were more harmful than helpful, leaving the patients disease, Semmelweis hypothesized that medical students car- tired, weak, and unable to fight the infection. Without effective ried “cadaver particles” from their autopsy studies into the de- treatments, the epidemic stopped only when the first frost arrived. livery rooms and that these “particles” resulted in puerperal 1. People who left the city seemed to have milder cases of fever. Semmelweis gained support for his hypothesis when a yellow fever or avoided the infection altogether. Explain doctor who sliced his finger during an autopsy died after show- why. ing symptoms similar to those of puerperal fever. Today we know that the primary cause of puerperal fever is a bacterium 2. The story mentions that the coming of the first frost in the genus Streptococcus (strep-tō-kok¿ŭs; see Figure 1.4), brought an end to the epidemic. Discuss the possible which is usually harmless on the skin or in the mouth but reasons why this would provide at least temporary relief causes severe complications when it enters the blood. from the epidemic. Semmelweis began requiring medical students to wash their hands with chlorinated lime water, a substance long used to eliminate the smell of cadavers. Mortality in the subsequent year dropped from 18.3% to 1.3%. Despite his success, Semmelweis The Gram stain is still the most widely used staining tech- was ridiculed by the director of the hospital and eventually was nique. It is one of the first steps carried out when bacteria are forced to leave. He returned to his native Hungary, where his in- being identified, and it is one of the procedures you will learn sistence on handwashing met with general approval when it in microbiology lab. Chapter 4 discusses the full procedure. continued to produce higher patient survival rates. Though his impressive record made it easier for later How Can We Prevent Infection doctors to institute changes, Semmelweis was unsuccessful in and Disease? 19 Learning Objectives From Greek nosos, meaning disease, and komein, meaning to care for (relating to a hospital). ✓ Identify four health care practitioners who did pioneering 20 From Latin puerperus, meaning childbirth. research in the areas of public health microbiology and epidemiology.  CHAPTER 1 A Brief History of Microbiology 17 gaining support for his method from most European doctors. He became severely depressed and was committed to a mental hospital, where he died from an infection of Streptococcus, the very organism he had fought for so long. Lister’s Antiseptic Technique Shortly after Semmelweis was rejected in Vienna, the English physician Joseph Lister (1827–1912) modified and advanced the idea of antisepsis21 in health care settings. As a surgeon, Lister was aware of the dreadful consequences that resulted from the infection of wounds. Therefore, he began spraying wounds, surgical incisions, and dressings with carbolic acid (phenol), a chemical that had previously proven effective in reducing odor and decay in sewage. Like Semmelweis, he initially met with some resistance, but when he showed that it reduced deaths among his patients by two-thirds, his method was accepted into common practice. In this manner, Lister vindicated Semmel- weis, became the founder of antiseptic surgery, and opened new fields of research into antisepsis and disinfection. ➤ Figure 1.18 Florence Nightingale. The founder of modern Nightingale and Nursing nursing, she was influential in introducing antiseptic technique into Florence Nightingale (1820–1910) (Figure 1.18) was a dedicated nursing practice. English nurse who introduced cleanliness and other antiseptic techniques into nursing practice. She was instrumental in setting standards of hygiene that saved innumerable lives during the Jenner’s Vaccine Crimean War of 1854–1856. One of her first requisitions in the In 1796, the English physician Edward Jenner (1749–1823) military hospital was for 200 scrubbing brushes, which she and tested the hypothesis that a mild disease called cowpox her assistants used diligently in the squalid wards. She next provided protection against potentially fatal smallpox. After arranged for each patient’s filthy clothes and dressings to be re- he intentionally inoculated a boy with pus collected from a placed or cleaned at a different location, thus removing many milkmaid’s cowpox lesion, the boy developed cowpox, which, sources of infection. She thoroughly documented statistical com- of course, he survived. When Jenner then infected the boy with parisons to show that poor food and unsanitary conditions in smallpox pus, he found that the boy had become immune23 to the hospitals were responsible for the deaths of many soldiers. smallpox. (Note that experiments that intentionally expose After the war, Nightingale returned to England, where she human subjects to deadly pathogens are unethical.) In 1798 actively exerted political pressure to reform hospitals and im- Jenner reported similar results from additional experiments, plement public health policies. Perhaps her greatest achievements demonstrating the validity of the procedure he named were in nursing education. For example, she founded the Nightin- vaccination after Vaccinia virus,24 the virus that causes cowpox. gale School for Nurses—the first of its kind in the world. Jenner invented vaccination (the term immunization is often used synonymously today), established a safe treatment for Snow and Epidemiology preventing smallpox, and began the field of immunology— Another English physician, John Snow (1813–1858), also played the study of the body’s specific defenses against pathogens. a key role in setting standards for good public hygiene to pre- Chapters 16–18 discuss immunology. vent the spread of infectious diseases. Snow had been studying Pasteur later capitalized on Jenner’s work by producing the propagation of cholera and suspected that the disease was weakened strains of various pathogens for use in preventing spread by a contaminating agent in water. In 1854, he mapped the serious diseases they cause. In honor of Jenner’s work with the occurrence of cholera cases during an epidemic in London cowpox, Pasteur used the term vaccine to refer to all weakened, and showed that they centered around a public water supply protective strains of pathogens. He subsequently developed on Broad Street. successful vaccines against fowl cholera, anthrax, and rabies. Though Snow did not know the cause of cholera, his careful documentation of the epidemic highlighted the critical need for 21From Greek anti, meaning against, and sepein, meaning putrefaction. 22From Greek epi, meaning upon; demos, meaning people; and logos, meaning word adequate sewage treatment and a pure water supply. His study or study. was the foundation for two branches of microbiology— 23From Latin immunis, meaning free. infection control and epidemiology,22 which is the study of the 24From Latin vacca, meaning cow. occurrence, distribution, and spread of disease in humans. 18 CHAPTER 1 A Brief History of Microbiology BIOLOGISTS MODERN DISCIPLINES In summary, the Golden Age of Microbiology was a time when Bacteriology (bacteria) researchers proved that living things come from other living Pre-1857 things, that microorganisms can cause fermentation and dis- Protozoology (protozoa) Leeuwenhoek Mycology (fungi) ease, and that certain procedures and chemicals can limit, pre- Parasitology (protozoa and animals) vent, and cure infectious diseases. These discoveries were made Phycology (algae) by scientists who applied the scientific method to biological in- vestigation, and they led to an explosion of knowledge in a Linnaeus Taxonomy number of scientific disciplines (Figure 1.19). Semmelweiss Snow Infection control Epidemiology The Modern Age of Microbiology The Golden Age of Learning Objective Microbiology (1857–1907) ✓ List four major questions that drive microbiological Industrial microbiology investigations today. Pasteur Pasteurization Food and beverage technology