cpe of Figure 13 The Sp us Generation Experiment.Pastcur's 。 ces Naturelle. flasks remained sealed.He proposed that air carried germs to the ters o e 1 Louis Pasteur.Pastcur (18895)workingin his support life dore Schwann (1810-1882)allow nter a flask con Thus the generation of maggots by decaving meat resulted from the presence of fly eggs.and meat did not spontancously gener Friedrich Schroder and Thedor von Dusch allowed air to entera Leeuwenhock's discovery of microorganisms renewed the Louis ted the results of his experi found th am b mutton en trapp cotton was plac d.Next he pla ed ni ner co ce that he ltal prop them ou of th th 13 79 imp iled the outions for a few minute the flasks were to thear.Pasteur ointed out that ing water for 3/4 of an hour,no growth took place as long as the growth occurred because dust and germs had been trapped on the
Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 Thus the generation of maggots by decaying meat resulted from the presence of fly eggs, and meat did not spontaneously generate maggots as previously believed. Similar experiments by others helped discredit the theory for larger organisms. Leeuwenhoek’s discovery of microorganisms renewed the controversy. Some proposed that microorganisms arose by spontaneous generation even though larger organisms did not. They pointed out that boiled extracts of hay or meat would give rise to microorganisms after sitting for a while. In 1748 the English priest John Needham (1713–1781) reported the results of his experiments on spontaneous generation. Needham boiled mutton broth and then tightly stoppered the flasks. Eventually many of the flasks became cloudy and contained microorganisms. He thought organic matter contained a vital force that could confer the properties of life on nonliving matter. A few years later the Italian priest and naturalist Lazzaro Spallanzani (1729–1799) improved on Needham’s experimental design by first sealing glass flasks that contained water and seeds. If the sealed flasks were placed in boiling water for 3/4 of an hour, no growth took place as long as the flasks remained sealed. He proposed that air carried germs to the culture medium, but also commented that the external air might be required for growth of animals already in the medium. The supporters of spontaneous generation maintained that heating the air in sealed flasks destroyed its ability to support life. Several investigators attempted to counter such arguments. Theodore Schwann (1810–1882) allowed air to enter a flask containing a sterile nutrient solution after the air had passed through a red-hot tube. The flask remained sterile. Subsequently Georg Friedrich Schroder and Theodor von Dusch allowed air to enter a flask of heat-sterilized medium after it had passed through sterile cotton wool. No growth occurred in the medium even though the air had not been heated. Despite these experiments the French naturalist Felix Pouchet claimed in 1859 to have carried out experiments conclusively proving that microbial growth could occur without air contamination. This claim provoked Louis Pasteur (1822–1895) to settle the matter once and for all. Pasteur (figure 1.2) first filtered air through cotton and found that objects resembling plant spores had been trapped. If a piece of the cotton was placed in sterile medium after air had been filtered through it, microbial growth appeared. Next he placed nutrient solutions in flasks, heated their necks in a flame, and drew them out into a variety of curves, while keeping the ends of the necks open to the atmosphere (figure 1.3). Pasteur then boiled the solutions for a few minutes and allowed them to cool. No growth took place even though the contents of the flasks were exposed to the air. Pasteur pointed out that no growth occurred because dust and germs had been trapped on the 6 Chapter 1The History and Scope of Microbiology Figure 1.2 Louis Pasteur. Pasteur (1822–1895) working in his laboratory. Figure 1.3 The Spontaneous Generation Experiment. Pasteur’s swan neck flasks used in his experiments on the spontaneous generation of microorganisms. Source: Annales Sciences Naturelle, 4th Series, Vol. 16, pp.1–98, Pasteur, L., 1861, “Mémoire sur les Corpuscules Organisés Qui Existent Dans L’Atmosphère: Examen de la Doctrine des Générations Spontanées
13 The Role ofM walls of the cuved necks.If the necks were broke growth com by161 but shown how to ke English physicist John Tyn 893)deal 187 During the lly heat-resistar forms of ba cteria.Working independe tence ofat-resant 1.Describe the field of microbiology in terms of the size of its 1.3 The Role of Microorganisms in Disease Indirect evidence that micro ns were agents of humar sed with Pasteur's studies on the involvement of micro Recognition of the Relationship ments were heat sterilized and phenol was used o between Microorganisms and Disease Although Fracastoro and a few others had sugg ested that invisi. Lister published his findings in867.It also provideds indi und inf se because The first direct demonstration of the ole of bac ia in caus accepte the criteria proposed by his former teacher.J ob Henk He nany diseases were due to microbial infe mice.h ated a pice spleen containing th by the French gov pores.When the ere injected into mice he study of fermentation.Pasteur was askec nthrax d ped.His criteria or proving t e causal re ggs pro
Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 1. The History and Scope of Microbiology © The McGraw−Hill Companies, 2002 walls of the curved necks. If the necks were broken, growth commenced immediately. Pasteur had not only resolved the controversy by 1861 but also had shown how to keep solutions sterile. The English physicist John Tyndall (1820–1893) dealt a final blow to spontaneous generation in 1877 by demonstrating that dust did indeed carry germs and that if dust was absent, broth remained sterile even if directly exposed to air. During the course of his studies, Tyndall provided evidence for the existence of exceptionally heat-resistant forms of bacteria. Working independently, the German botanist Ferdinand Cohn (1828–1898) discovered the existence of heat-resistant bacterial endospores (see chapter 3). 1. Describe the field of microbiology in terms of the size of its subject material and the nature of its techniques. 2. How did Pasteur and Tyndall finally settle the spontaneous generation controversy? 1.3 The Role of Microorganisms in Disease The importance of microorganisms in disease was not immediately obvious to people, and it took many years for scientists to establish the connection between microorganisms and illness. Recognition of the role of microorganisms depended greatly upon the development of new techniques for their study. Once it became clear that disease could be caused by microbial infections, microbiologists began to examine the way in which hosts defended themselves against microorganisms and to ask how disease might be prevented. The field of immunology was born. Recognition of the Relationship between Microorganisms and Disease Although Fracastoro and a few others had suggested that invisible organisms produced disease, most believed that disease was due to causes such as supernatural forces, poisonous vapors called miasmas, and imbalances between the four humors thought to be present in the body. The idea that an imbalance between the four humors (blood, phlegm, yellow bile [choler], and black bile [melancholy]) led to disease had been widely accepted since the time of the Greek physician Galen (129–199). Support for the germ theory of disease began to accumulate in the early nineteenth century. Agostino Bassi (1773–1856) first showed a microorganism could cause disease when he demonstrated in 1835 that a silkworm disease was due to a fungal infection. He also suggested that many diseases were due to microbial infections. In 1845 M. J. Berkeley proved that the great Potato Blight of Ireland was caused by a fungus. Following his successes with the study of fermentation, Pasteur was asked by the French government to investigate the pébrine disease of silkworms that was disrupting the silk industry. After several years of work, he showed that the disease was due to a protozoan parasite. The disease was controlled by raising caterpillars from eggs produced by healthy moths. Indirect evidence that microorganisms were agents of human disease came from the work of the English surgeon Joseph Lister (1827–1912) on the prevention of wound infections. Lister impressed with Pasteur’s studies on the involvement of microorganisms in fermentation and putrefaction, developed a system of antiseptic surgery designed to prevent microorganisms from entering wounds. Instruments were heat sterilized, and phenol was used on surgical dressings and at times sprayed over the surgical area. The approach was remarkably successful and transformed surgery after Lister published his findings in 1867. It also provided strong indirect evidence for the role of microorganisms in disease because phenol, which killed bacteria, also prevented wound infections. The first direct demonstration of the role of bacteria in causing disease came from the study of anthrax (see chapter 39) by the German physician Robert Koch (1843–1910). Koch (figure 1.4) used the criteria proposed by his former teacher, Jacob Henle (1809–1885), to establish the relationship between Bacillus anthracis and anthrax, and published his findings in 1876 (Box 1.1 briefly discusses the scientific method). Koch injected healthy mice with material from diseased animals, and the mice became ill. After transferring anthrax by inoculation through a series of 20 mice, he incubated a piece of spleen containing the anthrax bacillus in beef serum. The bacilli grew, reproduced, and produced spores. When the isolated bacilli or spores were injected into mice, anthrax developed. His criteria for proving the causal relationship between a microorganism and a specific disease are known as Koch’s postulates and can be summarized as follows: 1. The microorganism must be present in every case of the disease but absent from healthy organisms. 1.3 The Role of Microorganisms in Disease 7 Figure 1.4 Robert Koch. Koch (1843–1910) examining a specimen in his laboratory