Golden Age of Microbiology
Part 2 of Article: History is a kaleidoscope; The ancient past of Microbiology
The Theory of Biogenesis
Using the Theory of biogenesis, German scientist Rudolf Virchow questioned the evidence for spontaneous generation, claiming that living cells may only develop from preexisting living cells. Because he could not provide scientific proof, the debate over spontaneous creation raged on until 1861, when the French scientist Louis Pasteur finally put an end to it.
Louis Pasteur's Swan Neck Experiment and the Golden Age of Microbiology
The spontaneous generation controversy was a long-standing debate in biology about whether living organisms could arise from non-living matter. By the mid-19th century, the scientific consensus was that spontaneous generation was impossible, but there were still some proponents of the theory.
Louis Pasteur was a French chemist and microbiologist who is best known for his work on disproving spontaneous generation. In 1859, he designed a simple but elegant experiment to test the theory. Pasteur used a flask with a long, curved neck, known as a swan neck flask. He filled the flask with nutrient broth and boiled it to kill any existing microorganisms. Then, he bent the neck of the flask so that it was downward facing. This allowed air to enter the flask, but it prevented dust and other particles from falling into the broth. Pasteur left the flask open to the air for several weeks, but the broth remained clear and free of microorganisms. However, when he broke off the neck of the flask, the broth quickly became cloudy and teeming with microbial life.
This experiment proved that microorganisms do not arise spontaneously from non-living matter. Instead, they come from other microorganisms. Pasteur's work had a profound impact on the field of microbiology, and it is considered to be one of the most important experiments in the history of science.
He established decisively that heat can destroy microbial life and that techniques can be designed to prevent airborne germs from accessing nutritional environments. These findings represent the foundation of aseptic techniques, which prevent contamination by undesired bacteria and are now common practice in laboratories and many medical procedures.
The Golden Age of Microbiology
Pasteur's work on spontaneous generation helped to usher in the Golden Age of Microbiology, a period of rapid scientific progress in the field. During this time, scientists made many important discoveries about microorganisms, including their role in disease and their potential for industrial uses.
Some of the most notable achievements of the Golden Age of Microbiology include:
The discovery of the germ theory of disease, which led to the development of new treatments and vaccines for many infectious diseases.
The development of new methods for cultivating and studying microorganisms, which led to a better understanding of their biology and ecology.
The discovery of industrial uses for microorganisms, such as in beer brewing and cheesemaking.
Prior to Pasteur's work, it was widely believed that air was responsible for the conversion of sugars in these fluids into alcohol. However, Pasteur demonstrated that microorganisms called yeasts are responsible for this process, even in the absence of air. This process is known as fermentation.
Pasteur also discovered that different microorganisms called bacteria are responsible for souring and spoilage. In the presence of air, these bacteria convert alcohol into vinegar (acetic acid).
To address the spoilage problem, Pasteur developed a process of heating beer and wine to a temperature just high enough to kill the majority of the spoilage-causing bacteria. This process, known as pasteurization, is now widely used to reduce spoilage and kill potentially harmful bacteria in milk and other foods and beverages.
Pasteur himself made many important contributions to the Golden Age of Microbiology. The Golden Age of Microbiology (1857-1914) came to an end in the early 20th century, but the discoveries made during this period continue to have a profound impact on our lives today.
The discovery of the germ theory of disease, which led to the development of new treatments and vaccines for many infectious diseases.
Miasma Theory of Diseases
The miasma theory of diseases is an abandoned medical theory that held that diseases were caused by a miasma (Greek for "pollution"), a noxious form of "bad air", also known as night air. The theory held that epidemics were caused by miasma, emanating from rotting organic matter. Though miasma theory is typically associated with the spread of contagious diseases, some academics in the early nineteenth century suggested that the theory extended to other conditions as well, e.g. one could become obese by inhaling the odor of food. The miasma theory was the predominant medical theory for centuries, dating back to ancient Greece and Rome.
Humoral Theory of Diseases
Humoral theory is a medical system that originated in ancient Greece and Rome and was dominant in Western medicine for over 2,000 years. It was based on the belief that the human body contained four humors: blood, phlegm, yellow bile, and black bile ("sanguis"," "phlegm," "choler," and "melancholy" . Each humor was associated with a different temperament and a different set of physical characteristics. Health was seen as a state of balance between the four humors. If the humors became unbalanced, disease would result. The specific disease that developed would depend on which humor was in excess and which organs were affected. Humoral theory began to decline in the 17th century with the rise of Germ theory of diseases.
Germ theory of diseases
In 1865, Pasteur was called upon to help fight silkworm disease, which was ruining the silk industry throughout Europe. Years earlier, in 1835, Agostino Bassi, an amateur microscopist, had proved that another silkworm disease was caused by a fungus. In 1845 M. J. Berkeley (1803–1889) proved that the great potato blight of Ireland was caused by a water mold, and in 1853 Heinrich de Bary (1831–1888) showed that smut and rust fungi caused cereal crop diseases. Following these findings, Pasteur investigate the pèbrine 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.
Koch’s Postulates
Koch's postulates provide a robust and definitive framework for understanding the germ theory, elucidating the intricate connection between microorganisms and diseases. In 1876, the esteemed German physician Robert Koch expounded upon these principles, drawing upon the criteria originally formulated by his mentor, Jacob Henle, to establish the association between Bacillus anthracis and anthrax. Koch discovered rod-shaped bacteria now known as Bacillus anthracis in the blood of cattle that had died of anthrax. He recognized both actively dividing cells and dormant cells (spores) and developed techniques for studying them in vitro (outside a living organism).
Koch's seminal research involved a series of meticulous experiments. He commenced by inoculating materials from afflicted mice into healthy specimens, thereby inducing illness in the previously unaffected subjects. Additionally, Koch meticulously transferred anthrax through a sequence of 20 mice, incubating a portion of spleen tissue containing anthrax bacilli in beef serum. This procedure yielded the proliferation of microorganisms within the beef serum, ultimately resulting in the production of endospores. Subsequently, Koch employed these isolated bacteria and endospores to inoculate healthy mice, thereby precipitating illness in the previously uninfected mice. These experimental findings culminated in the formulation of specific criteria that elucidated the connection between microorganisms and distinct diseases, aptly referred to as Koch's postulates.
Koch's demonstration of Bacillus anthracis as the causative agent of anthrax received independent confirmation from Louis Pasteur and his colleague, who identified anthrax spores in the carcasses of deceased animals capable of infecting healthy ones. Following extensive research on anthrax, Koch formulated a comprehensive set of postulates that elucidated the etiology of tuberculosis.
In 1884, he conclusively attributed this malady to the rod-shaped bacterium known as Mycobacterium tuberculosis, an achievement that garnered him the Nobel Prize in Physiology or Medicine in 1905. Koch's postulates have since gained widespread acceptance in delineating the relationships between causative agents and numerous diseases. Nevertheless, it is worth noting that certain exceptions exist, such as Mycobacterium leprae, the causative agent of leprosy, which cannot be isolated in pure culture.
He invented a complicated staining process for species such as Mycobacteria and debunked the theory that tuberculosis was inherited. He was also instrumental in the discovery of Vibrio cholerae, the bacterium that causes cholera. Within a few years, Koch was appointed professor of hygiene at the University of Berlin, where he taught the first microbiology course ever given. He also created tuberculin, which he anticipated would be a tuberculosis vaccine.
Contributions in Microbial culture and isolation
Koch also discovered a way to grow bacteria in pure cultures, which included only one type of organism. He experimented with streaking bacterial solutions on potato slices and he developed culture media using meat extracts and protein digests, reasoning these were similar to body fluids. Initially he tried to solidify the media by adding gelatin. Yet, gelatin melts at incubator (body) temperature, and some microorganisms liquefy it even at ambient temperature. Finally, A better alternative was provided by Fanny Eilshemius Hesse , the wife of Walther Hesse , one of Koch’s assistants, proposed the usage of agar (a cookery thickening) to his bacteriological media. This formed a hard surface on which microorganisms could be dispersed thinly—so thinly, in fact, that some individual organisms were segregated from all others. Each organism then expanded into a colony of thousands of progeny. Koch's method for creating pure cultures is still in use today. Another important tool developed in Koch’s laboratory was a container for holding solidified media—the petri dish (plate), named after Richard Petri (1852–1921), who devised it.
Contributions Antiseptic techniques
Ignaz Philipp Semmelweis of Austria and Joseph Lister of England were both believed that microbes were to blame for diseases. Semmelweis saw a link between autopsies and puerperal fever. Several doctors went from performing autopsies to evaluating women in labor without even cleaning their hands.
Joseph Lister, an English surgeon, drew inspiration from Louis Pasteur's pioneering work on fermentation and putrefaction techniques. Lister applied this knowledge to advance the field of surgery by implementing antiseptic techniques aimed at preventing the ingress of microbes into surgical wounds. His approach encompassed the utilization of heat sterilization for surgical instruments and the application of phenol on surgical dressings. These innovative measures not only significantly reduced the risk of post-operative infections but also provided indirect substantiation for the Germ Theory of Diseases. He is considered as father of antiseptic surgery.
Contributions in Virology
In 1884, Charles Chamberland engineered a groundbreaking Porcelain Bacterial Filter, an innovation designed to effectively eliminate bacteria from water sources. Simultaneously, Martinus Beijerinck embarked on pioneering studies regarding the tobacco mosaic virus. Through meticulous experimentation, Beijerinck made a remarkable discovery: even after passing through Chamberland's bacterial filter, the infectious properties of the plant extract persisted. This revelation led Beijerinck to propose the existence of minute organisms, smaller than bacteria, which he aptly named "Filtered Virus." This term denoted specific pathogenic entities intimately associated with cellular structures.
Fast-forward to 1935, when the accomplished American scientist Wendell Stanley achieved a milestone by successfully crystallizing the tobacco mosaic virus. This achievement demonstrated that an agent possessing attributes akin to living organisms could also exhibit characteristics of chemical substances that were amenable to crystallization. Further analysis revealed that these virus crystals comprised ribonucleic acids and proteins.
The year 1939 marked another pivotal moment in virology history when the virus was first visualized using a commercial electron microscope, a technological marvel pioneered by Ernst Ruska and Max Knoll. This monumental development catapulted our understanding of viruses to new heights, ushering in an era of profound insights into these enigmatic entities.
1952 the American biologists Alfred Hershey and Martha Chase had demonstrated that the genetic material of some viruses is another nucleic acid, deoxyribonucleic acid (DNA). In 1953 the American postdoctoral student James Watson and the English biophysicist Francis Crick determined the structure of DNA.
Contributions in Immunology
The ancient Chinese possessed the knowledge that individuals scarred by smallpox were unlikely to contract the disease again. They ingeniously derived a preventive measure by collecting dried scales from smallpox lesions of recovering patients and transforming them into powders, which, when inhaled, conferred resistance to the disease. This method introduced a controlled exposure to weakened microbes, resulting in a mild form of smallpox and subsequent immunity. In 17th-century Europe, smallpox was rampant, initially introduced by Crusaders returning from the Near East in the 12th century. It wasn't until 1717 that Lady Mary Ashley Montagu, the wife of the British ambassador to Turkey, brought a novel immunization technique to England. This technique involved saturating a thread with fluid from smallpox blisters and passing it through a small incision in the arm. These procedures known as Variolation.
In the late 18th century, Edward Jenner made a groundbreaking observation. He noted that milkmaids who contracted cowpox did not succumb to smallpox. Inspired by this observation, Jenner inoculated his own son with fluid from a cowpox blister and subsequently exposed him to smallpox. Remarkably, the child remained in good health. The term "vaccinia" derived from the Latin word "Vacca" meaning cow, was coined to refer to the cowpox virus.
Building on this progress, Louis Pasteur and Pierre Roux conducted pivotal studies on chicken cholera in 1879. Their research revealed that prolonged incubation of bacterial cultures led to the attenuation of the pathogen's virulence. By inoculating healthy chickens with this attenuated bacterial culture, they remained resilient and developed resistance when exposed to virulent cultures. In honor of Edward Jenner's pioneering work, Pasteur referred to the attenuated culture as a "vaccine," marking a significant milestone in the history of immunization.
Pasteur also developed a rabies vaccine using a weakened strain of the Rabies virus. Over the course of these experiments, Pasteur received Joseph Meister, a nine-year-old kid who had been bitten by a rabid dog. Pasteur consented to try immunization because the boy's death was certain in the absence of treatment. For the next ten days, Joseph was injected 13 times with increasingly virulent strains of the attenuated virus and he survived. In gratitude for Pasteur’s development of vaccines, people from around the world contributed to the construction of the Pasteur Institute in Paris, France. One of the initial tasks of the institute was vaccine production.
Emil von Behring and Shibasaburo Kitasato made a groundbreaking contribution to the field of immunology when they identified and isolated the toxin produced by the diphtheria bacillus. Their pivotal work involved the inoculation of this toxin into rabbits to generate antitoxin, a pioneering achievement in the early understanding of immunotherapy. Furthermore, they extended their efforts to prepare antitoxin for tetanus, expanding the scope of their immunological discoveries. These seminal findings laid the foundation for a deeper comprehension of antibodies and humoral immunity.
In parallel, Elie Metchnikoff made significant strides in immunology by unveiling the phenomenon of white blood cells engulfing bacteria. Coined as "Phagocytes," these cells were aptly named for their function, as "phago" derives from the Greek term meaning "cell eating." Metchnikoff's discovery shed light on the essential process now known as Phagocytosis, further enriching our understanding of the intricate mechanisms underlying the immune system.
Contributions in Chemotherapy
The pursuit of eliminating pathogenic microorganisms paved the way for the field of chemotherapy, involving the application of chemical substances for the treatment of diseases. Among these substances, antibiotics are naturally produced by bacteria or fungi and exhibit antagonistic properties against other microorganisms. Conversely, synthetic drugs, synthesized within laboratory settings for therapeutic purposes, play a crucial role in modern medicine.
In the first century A.D., Pedanius Dioscorides, often regarded as the father of pharmacognosy, meticulously compiled a comprehensive five-volume work cataloging numerous substances derived from plants. Notable examples include digitalis, curare, ephedrine, and morphine, all of which found their place in the Materia Medica. Fast forward to the early 16th century, Swiss physician Aureolus Paracelsus employed metallic elements such as antimony for combating general infections and mercury for treating syphilis. The mid-17th century witnessed another milestone when Thomas Sydenham introduced the use of cinchona tree bark, rich in quinine, as a remedy for malaria.
However, the turning point in chemotherapy came through the work of Paul Ehrlich, who is credited with coining the term "Chemotherapy." His groundbreaking observation revealed that certain dyes selectively stained microorganisms while sparing animal cells, suggesting the potential for these dyes and other chemicals to kill microorganisms without harming the host animal cells. These initial synthetic chemicals or dyes were aptly referred to as "Magic bullets." Through extensive testing, Ehrlich identified Arsenophenylglycine (Compound 418) as effective against sleeping sickness and Salvarsan (Compound 606) as a potent weapon against syphilis.
In 1992, the Scottish physician and bacteriologist Alexander Fleming made a pivotal discovery regarding the antimicrobial properties of Lysozyme, an enzyme naturally occurring in tears, saliva, and sweat. This marked a significant advancement in the field of microbiology. Fleming's groundbreaking work did not stop there. In 1928, he stumbled upon the first antibiotics unintentionally while examining Staphylococcus bacterial plates contaminated with the Penicillium mold. He aptly named this newfound antibiotic "penicillin."
Following these discoveries, Ernst Chain and Howard Florey played a crucial role in the commercial purification of penicillin antibiotics, transforming it into a versatile chemotherapeutic agent. This development marked a turning point in medical science.
In 1935, the utilization of Prontosil Rubrum, a reddish dye containing Sulfonamide, revolutionized the treatment of streptococcal infections. German scientist Gerhard Domagk harnessed this innovation to pioneer the creation of sulfa drugs, eventually leading to the development of Isoniazid for the treatment of tuberculosis.
Further progress in the field of antibiotics emerged in 1939 when French microbiologist Rene Dubos uncovered tyrothricin, an antibiotic sourced from soil bacteria. This discovery inspired Selman A. Waksman, who delved into studying the antibiotic properties of soil bacteria, specifically actinomycetes. In 1941, he coined the term "antibiotics" to describe actinomycin and other isolated products such as neomycin, chloramphenicol, and chlortetracycline. In 1943, he led to a historic moment in antibiotic research when streptomycin, an effective and less toxic antibiotic, was identified. This breakthrough was crucial in the treatment of tuberculosis.
Italian microbiologist Giuseppe Brotzu's contributions cannot be understated. He aided in the discovery of Cephalosporin, an antibiotic produced by the fungus Cephalosporium acremonium, which originated from sources other than soil, notably the sea.
Contributions in Microbial Ecology
The Russian microbiologist Sergei Winogradsky made significant strides by revealing how soil bacteria could oxidize various inorganic compounds, such as sulfur, ammonia, and iron, to obtain energy while incorporating carbon dioxide, similar to photosynthesis. He invented a tool to study these processes was a long, sealed column of muddy soil, now called a Winogradsky column. He also isolated anaerobic nitrogen-fixing soil bacteria and conducted studies on cellulose decomposition. Martinus Beijerinck's work complemented these findings by isolating the aerobic nitrogen-fixing bacterium Azotobacter from root nodules and sulfate-reducing bacteria. Both researchers contributed to the development of enrichment-culture techniques and the utilization of selective media in microbiology.
It is important to note that microbiology remains an ever-evolving field. Today's discoveries invariably become tomorrow's historical landmarks. Consequently, providing a comprehensive history of microbiology proves challenging, as it is a field characterized by ongoing research and continual advancements. The period from 1874 to 1917 stands out as the golden age of microbiology, yet new knowledge is continually emerging, sometimes superseding previous findings.
References:
Prescott’s principles of microbiology / Joanne M. Willey, Linda M. Sherwood, Christopher J. Woolverton 2009
Microbiology : an introduction / Gerard J. Tortora, Berdell R. Funke, Christine L. Case. 11th ed.
Microbiology: principles and explorations/Jacquelyn G. Black. 9th ed