A History of Microbiology: The Theory of Spontaneous Generation

History of microbiology, Notes, MCQ, PDF, Books

Detailed Timeline of Main Events in Microbiology History

1749-1823 (Lifespan): Edward Jenner’s Work on Smallpox

1796: Edward Jenner proves that inoculating people with pus from cowpox lesions provides protection against smallpox, based on observations of milkmaids’ immunity.
1798: Jenner publishes his results on 23 successful vaccinators, introducing the term “vaccination” (from Latin ‘Vacca’ meaning cow). This replaces the riskier technique of immunizing with actual smallpox material.

Mid-18th to Mid-19th Century: Debates on Spontaneous Generation

Pre-17th Century (Implied): The prevailing “theory of spontaneous generation” suggests microorganisms arise from lifeless matter.
Francesco Redi’s Contribution (Implied, earlier than Needham): Redi disputes spontaneous generation by demonstrating that fly maggots do not arise from decaying meat if flies are prevented from accessing it.
John Needham’s Advancement (Implied mid-18th century): John Needham advances the theory of spontaneous generation, arguing that microorganisms can arise from lifeless matter like beef broth.
Lazzaro Spallanzani’s Disputation (Implied mid-18th century): Lazzaro Spallanzani disputes Needham’s theory by showing that boiled broth, when sealed, does not give rise to microscopic life.

Mid-19th Century: Pasteur’s Contributions to Microbiology

1858: Louis Pasteur resolves the controversy of spontaneous generation versus biogenesis. He proves that microorganisms are not spontaneously generated but arise from other microorganisms, using his “swan-necked flasks” experiments. This puts the notion of spontaneous generation to rest.
1867: Lord Joseph Lister develops a system of antiseptic surgery, applying phenol to prevent wound infections, concluding that wound infections are due to microorganisms. He also devises a method to spray carbolic acid in operating theaters to create an antiseptic environment, becoming known as the “Father of Antiseptic Surgery.”
1880: Pasteur discovers that old cultures of Chicken cholera germs lose their ability to transmit disease. He uses this principle to produce immunity without the risk of disease, showing that chickens inoculated with the old culture become immune to fresh, potent germs.
Post-1880: Encouraged by his success with anthrax vaccination (applying Jenner’s principle), Pasteur works on a vaccine for hydrophobia (rabies).
1884: French microbiologist Charles Chamberland invents the Pasteur-Chamberland filter, capable of removing all bacteria from a solution.
Late 19th Century (Implied): Louis Pasteur speculates about a pathogen for rabies too small to be detected by microscopes, as he was unable to find a causative agent.

Late 19th Century: Final Blows to Spontaneous Generation and Germ Theory Establishment

1877: John Tyndall delivers a “final blow” to spontaneous generation by demonstrating that dust carries germs and that sterile broth remains free of microbial growth indefinitely if no dust is present. He also discovers highly resistant bacterial structures (endospores) and develops “Tyndallisation” (prolonged/intermittent heating to kill spores).
1890: Robert Koch establishes “Koch’s four postulates” for proving that an organism causes a specific disease.
Late 19th Century (Overall): The combined efforts of many scientists, particularly Pasteur and Robert Koch, establish the “Germ Theory of Disease,” which states that invisible microorganisms cause disease.

Late 19th to Mid-20th Century: The Discovery and Understanding of Viruses

1892: Russian biologist Dmitri Ivanovsky uses the Pasteur-Chamberland filter to study what becomes known as the tobacco mosaic virus. He finds crushed leaf extracts remain infectious even after bacterial filtration but suggests it might be a bacterial toxin.
1898: Dutch microbiologist Martinus Beijerinck repeats Ivanovsky’s experiments and becomes convinced of a new infectious agent. He observes it multiplies only in dividing cells, calls it a “contagium vivum fluidum,” and reintroduces the word “virus.”
Early 20th Century: English bacteriologist Frederick Twort discovers bacteriophages (viruses that infect bacteria).
1929: Sir Alexander Fleming discovers penicillin, the first “wonder drug.”
1931: American pathologist Ernest William Goodpasture and Alice Miles Woodruff successfully grow influenza and other viruses in fertilized chicken eggs.
1931: German engineers Ernst Ruska and Max Knoll invent electron microscopy, enabling the first images of viruses to be obtained.
1935: American biochemist and virologist Wendell Meredith Stanley examines the tobacco mosaic virus, finding it is mostly made of protein. Soon after, it is separated into protein and RNA parts.
Second half of the 20th Century: This period is described as the “golden age of virus discovery,” with most documented animal, plant, and bacterial viruses found.

Ongoing (Implied):

Bacterial resistance to antibiotics renews interest in the therapeutic use of bacteriophages.
Modern immunization programs for diseases like diphtheria, tetanus, pertussis, polio, and measles are founded on the principles established by Jenner and Pasteur.
Aseptic techniques introduced by Lister using physical and chemical agents are still in use today.

Cast of Characters

Scientists and Physicians:

Louis Pasteur (1822-1895): A highly influential French microbiologist and chemist. He definitively disproved the theory of spontaneous generation with his swan-necked flask experiments in 1858. He also developed the first vaccines for diseases like chicken cholera and rabies, laying foundational work for modern immunization and contributing significantly to the Germ Theory of Disease.
Robert Koch (1843-1910): A German physician and microbiologist. He established “Koch’s four postulates” in 1890, a set of criteria to establish a causative relationship between a microbe and a disease. His work, alongside Pasteur’s, was crucial in establishing the Germ Theory of Disease.
Edward Jenner (1749-1823): An English physician. He is credited with preventing smallpox by observing that milkmaids who contracted cowpox were immune to smallpox. In 1796, he pioneered vaccination by inoculating people with cowpox pus, a process he named “vaccination” (from “Vacca” meaning cow).
Lord Joseph Lister (1827-1912): An English surgeon, known as the “Father of Antiseptic Surgery.” In 1867, he developed and introduced antiseptic techniques in surgery using phenol (carbolic acid) to prevent wound infections, recognizing that microorganisms caused them. He also devised methods for antiseptic environments in operating theatres.
John Needham (1713-1781): An English cleric. He was a proponent of the theory of spontaneous generation, arguing that microorganisms could arise from lifeless matter like beef broth.
Francesco Redi (1626-1697): An Italian physician and poet. He was an early challenger to spontaneous generation, demonstrating that maggots did not spontaneously appear on decaying meat if flies were prevented from laying eggs on it.
Lazzaro Spallanzani (1729-1799): An Italian priest, biologist, and physiologist. He disputed the theory of spontaneous generation by showing that boiled and sealed broth would not give rise to microscopic forms of life, further undermining Needham’s claims.
John Tyndall (1820–1893): An English physicist. He delivered a “final blow” to the theory of spontaneous generation in 1877 by demonstrating that dust carried germs and was responsible for microbial growth in air-exposed broth. He also discovered heat-resistant bacterial endospores and developed “Tyndallisation” for sterilization.
Dmitri Ivanovsky (1864-1920): A Russian biologist. In 1892, he used the Pasteur-Chamberland filter to study what would become known as the tobacco mosaic virus, noting that filtered extracts from infected plants remained infectious even after bacteria were removed. He initially speculated about a bacterial toxin.
Charles Chamberland (1851-1908): A French microbiologist, working with Pasteur. In 1884, he invented the Pasteur-Chamberland filter, a crucial tool with pores small enough to remove all bacteria from a solution, which later became essential in the discovery of viruses.
Martinus Beijerinck (1851-1931): A Dutch microbiologist. In 1898, he repeated Ivanovsky’s experiments and became convinced that the filtered solution contained a new form of infectious agent. He observed it multiplied only in living, dividing cells and re-introduced the word “virus,” calling it a “contagium vivum fluidum” (soluble living germ).
Frederick Twort (1877-1950): An English bacteriologist. In the early 20th century, he discovered bacteriophages, a group of viruses that specifically infect bacteria.
Sir Alexander Fleming (1881-1955): A Scottish physician and bacteriologist. He is credited with the groundbreaking discovery of penicillin, the first “wonder drug,” in 1929.
Ernest William Goodpasture (1886-1960): An American pathologist. In 1931, alongside Alice Miles Woodruff, he successfully grew influenza and several other viruses in fertilized chicken eggs, a significant advancement for virology.
Alice Miles Woodruff (1900-1981): An American scientist. In 1931, alongside Ernest William Goodpasture, she successfully grew influenza and several other viruses in fertilized chicken eggs.
Ernst Ruska (1906-1988): A German electrical engineer. In 1931, along with Max Knoll, he invented the electron microscope, which enabled the first visualization of viruses.
Max Knoll (1897-1969): A German electrical engineer. In 1931, along with Ernst Ruska, he invented the electron microscope, which allowed for the first images of viruses to be obtained.
Wendell Meredith Stanley (1904-1971): An American biochemist and virologist. In 1935, he examined the tobacco mosaic virus, finding it was mostly made of protein, and shortly after, it was separated into its protein and RNA components.

Scientist and theories:

Abiogenesis vs. Biogenesis

Theory of spontaneous generation, which stated that microorganisms arise from lifeless matter such as beef broth.
An English cleric named John Needham advanced spontaneous generation.
This theory was disputed by Francesco Redi, who showed that fly maggots do not arise from decaying meat (as others believed) if the meat is covered to prevent the entry of flies.
Lazzaro Spallanzani disputed the theory by showing that boiled broth would not give rise to microscopic forms of life.
Pasteur had to disprove spontaneous generation to sustain his theory, and he therefore devised a series of swan‐necked flasks filled with broth.
He left the flasks of broth open to the air, but the flasks had a curve in the neck so that microorganisms would fall into the neck, not the broth.

The flasks did not become contaminated.
Pasteur’s experiments put to rest the notion of spontaneous generation.
Pasteur, thus in 1858 resolved the controversy of spontaneous generation versus biogenesis and proved that microorganisms are not spontaneously generated from inanimate matter but arise from other microorganisms.

John Tyndall (1820–1893):

An English physicist, Gave a final blow to spontaneous generation in 1877.

He conducted experiments in an aseptically designed box to prove that dust indeed carried the germs.
He demonstrated that if no dust was present, sterile broth remained free of microbial growth for an indefinite period even if it was directly exposed to air.
He discovered highly resistant bacteria structures, later known as endospores.
Prolonged boiling or intermittent heating was necessary to kill these spores, and to make the infusion completely sterilized, a process known as Tyndallisation.

Chicken cholera experiment

In 1880, Pasteur found that Chicken cholera germs from an old culture that had been around for some time lost their ability to transmit the disease à The inoculated chickens did not die.
He repeated what he had done but with a fresh culture of chicken cholera germs.
Pasteur reasoned that a new culture would provide more potent germs.
He found a way of producing resistance without the risk of the disease.
Two groups of chickens were inoculated; one that had been given the old culture and one group that had not.
Those chickens that had been given the old culture survived, and those that had not died.
The chickens that had been inoculated with the old culture had become immune to chicken cholera.
Pasteur believed that their bodies had used the weaker strain of germ to form a defense against the more powerful germs in the fresher culture.

Koch’s four postulates (1890):

The organism causing the disease can be found in sick individuals but not in healthy ones.
The organism can be isolated and grown in pure culture.
The organism must cause the disease when it is introduced into a healthy animal.
The organism must be recovered from the infected animal and shown to be the same as the organism that was introduced.
The combined efforts of many scientists and most importantly Pasteur and Robert Koch established the Germ theory of disease.

The idea that invisible microorganisms are the cause of the disease is called germ theory.

Edward Jenner (1749-1823):

An English physician was the first to prevent smallpox.

Impressed by the observation that countryside milkmaids who contracted cowpox (Cowpox is a milder disease caused by a virus closely related to smallpox) while milking were subsequently immune to smallpox.
In 1796 he proved that inoculating people with pus from cowpox lesions provided protection against smallpox.
Jenner in 1798 published his results on 23 successful vaccinators.
Eventually, this process was known as vaccination, based on the Latin word ‘Vacca’ meaning cow.
He called the attenuated cultures as vaccines and the process as vaccination.
Thus the use of cowpox virus to protect smallpox disease in humans became popular replacing the risky technique of immunizing with actual smallpox material.
Jenner’s experimental significance was realized by Pasteur who next applied this principle to the prevention of anthrax and it worked.
Encouraged by the successful prevention of anthrax by vaccination, Pasteur marched ahead towards the service of humanity by making a vaccine for hydrophobia or rabies (a disease transmitted to people by bites of dogs and other animals).
As with Jenner’s vaccination for smallpox, the principle of the preventive treatment of rabies also worked fully which laid the foundation of modern immunization programs against many dreaded diseases like diphtheria, tetanus, pertussis, polio, measles, etc.

Lord Joseph Lister (1827-1912):

English surgeon is known for his notable contribution to the antiseptic treatment for the prevention and cure of wound infections.
Lister concluded that wound infections too were due to microorganisms.
In 1867, he developed a system of antiseptic surgery designed to prevent microorganisms by the application of phenol.
He also devised a method to destroy microorganisms in the operation theatre by spraying a fine mist of carbolic acid into the air, thus producing an antiseptic environment.
He first to introduce aseptic techniques for the control of microbes by the use of physical and chemical agents which are still in use today.
Because of this notable contribution, Joseph Lister is known as the Father of Antiseptic surgery.

Sir Alexander Fleming (Scottish physician and bacteriologist): The credit for the discovery of the first ‘wonder drug’ penicillin in 1929 goes to Fleming.

Dmitri Ivanovsky and Virus:

Louis Pasteur was unable to find a causative agent for rabies and speculated about a pathogen too small to be detected by microscopes.
In 1884, the French microbiologist Charles Chamberland invented the Pasteur-Chamberland filter with pores small enough to remove all bacteria from a solution passed through it.
In 1892, the Russian biologist Dmitri Ivanovsky used this filter to study what is now known as the tobacco mosaic virus: crushed leaf extracts from infected tobacco plants remained infectious even after filtration to remove bacteria.
Ivanovsky suggested the infection might be caused by a toxin produced by bacteria, but did not pursue the idea.
At the time it was thought that all infectious agents could be retained by filters and grown on a nutrient medium—this was part of the germ theory of disease.
In 1898, the Dutch microbiologist Martinus Beijerinck repeated the experiments and became convinced that the filtered solution contained a new form of infectious agent.
He observed that the agent multiplied only in cells that were dividing, but as his experiments did not show that it was made of particles, he called it a contagium vivum fluidum (soluble living germ) and re-introduced the word virus.
In the early 20th century, the English bacteriologist Frederick Twort discovered a group of viruses that infect bacteria, now called bacteriophages (or commonly ‘phages’).
The development of bacterial resistance to antibiotics has renewed interest in the therapeutic use of bacteriophages.

In 1931, when the American pathologist Ernest William Goodpasture and Alice Miles Woodruff grew influenza and several other viruses in fertilized chicken eggs.
The first images of viruses were obtained upon the invention of electron microscopy in 1931 by German engineers Ernst Ruska and Max Knoll.
In 1935, American biochemist and virologist Wendell Meredith Stanley examined the tobacco mosaic virus and found it was mostly made of protein.
A short time later, this virus was separated into protein and RNA parts.
The second half of the 20th century was the golden age of virus discovery and most of the documented species of animal, plant, and bacterial viruses were discovered during these years.

Microbiology MCQ with answers:

Quiz

Instructions: Answer each question in 2-3 sentences.

How did Francesco Redi challenge the theory of spontaneous generation?
What was Lazzaro Spallanzani’s contribution to disproving spontaneous generation?
Describe the design and outcome of Louis Pasteur’s swan-necked flask experiment.
What did John Tyndall’s experiments demonstrate regarding dust and microbial growth?
Explain the key outcome of Pasteur’s chicken cholera experiment and its significance.
List two of Koch’s four postulates and explain their purpose.
How did Edward Jenner develop the smallpox vaccine, and what was its origin?
What significant contribution did Joseph Lister make to surgical practices?
How did Dmitri Ivanovsky and Martinus Beijerinck’s work contribute to the understanding of viruses?
What technological advancement was crucial for obtaining the first images of viruses, and when did this occur?

Answer Key

Francesco Redi challenged spontaneous generation by demonstrating that maggots on decaying meat did not arise spontaneously. He showed that if meat was covered to prevent flies from accessing it, no maggots appeared, indicating flies were the source.
Lazzaro Spallanzani disputed spontaneous generation by showing that broth, after being boiled to kill existing microorganisms, would not spontaneously give rise to new microscopic life forms if kept sealed from the air. This suggested that life did not arise from inanimate matter.
Pasteur’s swan-necked flasks had a curved neck that allowed air in but trapped airborne microorganisms in the curve, preventing them from reaching the broth. The broth remained sterile, proving that contamination came from external microorganisms, not spontaneous generation.
John Tyndall demonstrated that dust carried germs by conducting experiments in an aseptically designed box. He showed that if no dust was present, sterile broth remained free of microbial growth indefinitely, even when exposed to air, thus linking microbial growth to airborne particles.
Pasteur’s chicken cholera experiment showed that an old culture of chicken cholera germs lost its virulence but could still induce immunity. Chickens inoculated with the old culture survived a subsequent infection with a fresh, potent culture, demonstrating the principle of vaccination.
One postulate states that the organism causing the disease can be found in sick individuals but not healthy ones. Another states that the organism must cause the disease when introduced into a healthy animal. These postulates aim to establish a causal link between a specific microbe and a specific disease.
Edward Jenner developed the smallpox vaccine after observing that milkmaids who contracted cowpox were immune to smallpox. He inoculated people with pus from cowpox lesions, which provided protection against smallpox, leading to the term “vaccination” (from Latin ‘Vacca’ for cow).
Joseph Lister made a notable contribution to antiseptic surgery by developing a system to prevent wound infections. He applied phenol to wounds and sprayed carbolic acid into the operating room to create an antiseptic environment, significantly reducing post-operative infections.
Ivanovsky used a filter to show that infectious agents for tobacco mosaic disease could pass through filters that retained bacteria, but he attributed it to a toxin. Beijerinck repeated the work, concluding that a new, filterable, multiplying agent was responsible, which he called a contagium vivum fluidum, re-introducing the term virus.
The first images of viruses were obtained with the invention of electron microscopy in 1931 by German engineers Ernst Ruska and Max Knoll. This technological advancement allowed scientists to visualize structures previously too small to be seen with traditional light microscopes.

Essay Format Questions

Compare and contrast the contributions of Francesco Redi, Lazzaro Spallanzani, Louis Pasteur, and John Tyndall in disproving the theory of spontaneous generation. How did each scientist’s experiments build upon previous work to definitively refute the theory?
Discuss the development of vaccination, tracing its origins from Edward Jenner’s work with smallpox to Louis Pasteur’s application of the principle to diseases like chicken cholera and rabies. What common principle links these early vaccination efforts?
Explain Koch’s four postulates and their significance in establishing the Germ Theory of Disease. How did the combined efforts of scientists like Pasteur and Koch fundamentally change the understanding of disease causation?
Detail Joseph Lister’s role in the development of antiseptic surgery. What observations led him to his conclusions, and what specific methods did he implement to prevent wound infections? How did his work impact medical practice?
Describe the historical progression of understanding viruses, from Louis Pasteur’s initial speculations to the discoveries of Dmitri Ivanovsky, Martinus Beijerinck, and the eventual visualization of viruses. What challenges did early microbiologists face in studying these agents, and how were these overcome?

Glossary of Key Terms

Abiogenesis: The obsolete theory that living organisms can arise spontaneously from non-living matter; also known as spontaneous generation.
Antiseptic Surgery: Surgical practices aimed at preventing microbial infection of wounds, pioneered by Joseph Lister through the use of chemical agents like phenol.
Bacteriophages (Phages): A group of viruses that specifically infect and replicate within bacteria.
Biogenesis: The principle that living organisms arise only from other living organisms.
Contagium Vivum Fluidum: A Latin term meaning “soluble living germ,” used by Martinus Beijerinck to describe the filterable infectious agent that caused tobacco mosaic disease, before it was definitively identified as a virus.
Cowpox: A milder disease caused by a virus closely related to smallpox, which provided immunity to smallpox in humans.
Electron Microscopy: A type of microscopy that uses a beam of electrons to create an image, allowing for much higher magnification and resolution than light microscopy, crucial for visualizing viruses.
Endospores: Highly resistant bacterial structures discovered by John Tyndall, which require prolonged or intermittent heating to sterilize.
Germ Theory of Disease: The scientific theory that certain diseases are caused by specific microscopic organisms (germs).
Koch’s Postulates: A set of four criteria established by Robert Koch to demonstrate that a specific microorganism causes a specific disease.
Phenol (Carbolic Acid): A chemical compound used by Joseph Lister as an antiseptic to prevent wound infections and sterilize surgical environments.
Spontaneous Generation: The discredited theory that living organisms can arise from non-living matter; synonymous with abiogenesis.
Swan-necked Flasks: Flasks designed by Louis Pasteur with an S-shaped neck that allowed air exchange but prevented airborne microbes from reaching the sterile broth, used to disprove spontaneous generation.
Tobacco Mosaic Virus (TMV): The first virus to be discovered, studied by Ivanovsky and Beijerinck, affecting tobacco plants.
Tyndallisation: A process of intermittent heating and cooling to achieve sterilization, particularly effective against endospores, developed by John Tyndall.
Vaccination: The process of administering a weakened or attenuated form of a pathogen (or related pathogen) to a host to induce immunity, a term coined by Edward Jenner.
Virus: A submicroscopic infectious agent that replicates only inside the living cells of an organism.

What was the theory of spontaneous generation, and how was it disproven?

The theory of spontaneous generation, also known as abiogenesis, proposed that living organisms, particularly microorganisms, could arise from non-living matter, such as beef broth. This idea was advanced by individuals like John Needham. However, it was thoroughly disproven through a series of experiments. Francesco Redi demonstrated that maggots on decaying meat originated from flies, not the meat itself. Lazzaro Spallanzani showed that boiled broth remained free of microscopic life if sealed from the air. Louis Pasteur delivered the final blow with his famous swan-necked flasks; the design allowed air in but trapped dust and microorganisms in the curved neck, preventing contamination of the broth. This definitively proved that microorganisms arise from other microorganisms (biogenesis), not spontaneously. John Tyndall further supported this by showing that even with direct air exposure, sterile broth remained clear if no dust (which carried germs) was present, and discovered resistant bacterial endospores that required prolonged boiling for sterilization (Tyndallisation).

How did the concept of vaccination originate and evolve?

The concept of vaccination began with Edward Jenner in the late 18th century. Jenner observed that milkmaids who contracted cowpox were immune to smallpox. In 1796, he successfully demonstrated that inoculating people with pus from cowpox lesions provided protection against smallpox, coining the term “vaccination” from the Latin word “vacca” (cow). This replaced the riskier practice of immunizing with actual smallpox material. Louis Pasteur later applied this principle to other diseases, developing vaccines for anthrax and rabies. Pasteur’s work, inspired by Jenner, laid the foundation for modern immunization programs against numerous dreaded diseases like diphtheria, tetanus, pertussis, polio, and measles.

What is the Germ Theory of Disease, and who were key figures in its establishment?

The Germ Theory of Disease is the fundamental idea that invisible microorganisms are the cause of many diseases. This theory was established through the combined efforts of many scientists, most notably Louis Pasteur and Robert Koch. Koch contributed significantly by developing his “four postulates” in 1890, which provided a systematic way to prove that a specific microorganism causes a particular disease: the organism must be found in sick but not healthy individuals, it must be isolable and grown in pure culture, it must cause the disease when introduced into a healthy animal, and it must be recovered from the infected animal and identified as the original organism.

How did Joseph Lister contribute to surgical safety and the control of microbes?

Lord Joseph Lister, an English surgeon, is renowned as the “Father of Antiseptic Surgery” for his pioneering contributions to preventing and treating wound infections. He concluded that wound infections were caused by microorganisms. In 1867, he developed a system of antiseptic surgery by applying phenol to prevent microbial growth. He also devised a method to sterilize the operating environment by spraying a fine mist of carbolic acid into the air, creating an antiseptic field. Lister was the first to introduce aseptic techniques for controlling microbes using physical and chemical agents, many of which are still in use today.

What was the significance of Alexander Fleming’s discovery?

Sir Alexander Fleming, a Scottish physician and bacteriologist, is credited with the serendipitous discovery of the first “wonder drug,” penicillin, in 1929. This discovery of an antibiotic revolutionized medicine by providing an effective means to combat bacterial infections, significantly reducing mortality rates from previously untreatable diseases.

How were viruses discovered, and what challenges did their study present?

The discovery of viruses began with a mystery: Louis Pasteur couldn’t find a causative agent for rabies, speculating about a pathogen too small for microscopes. In 1884, Charles Chamberland invented a filter that could remove all known bacteria. In 1892, Russian biologist Dmitri Ivanovsky used this filter to study the tobacco mosaic disease, finding that filtered extracts from infected plants remained infectious, even though they were bacteria-free. He initially suggested a bacterial toxin, but Dutch microbiologist Martinus Beijerinck in 1898 became convinced it was a new infectious agent that multiplied only in dividing cells. He called it a contagium vivum fluidum (soluble living germ) and reintroduced the word “virus.” The study of viruses was challenging because they were too small to be seen with early microscopes and couldn’t be grown on standard nutrient media like bacteria. The invention of electron microscopy in 1931 by Ernst Ruska and Max Knoll finally provided the first images of viruses, confirming their particulate nature.

What is the “chicken cholera experiment” and what did Pasteur learn from it?

The chicken cholera experiment, conducted by Louis Pasteur in 1880, was pivotal in understanding attenuated vaccines. Pasteur observed that an old culture of chicken cholera germs had lost its ability to cause disease; chickens inoculated with this old culture did not die. When he subsequently inoculated these same chickens with a fresh, potent culture of chicken cholera germs, they survived, while a control group of unvaccinated chickens died. Pasteur reasoned that the weaker, “old” strain of germs had allowed the chickens’ bodies to develop a defense (immunity) against the more powerful, “fresh” germs. This accidental discovery demonstrated the principle of attenuation—weakening a pathogen to create a vaccine that induces immunity without causing severe disease—a cornerstone of modern immunology.

What are Koch’s four postulates, and why are they important in microbiology?

Koch’s four postulates, developed by Robert Koch in 1890, are a set of criteria used to establish a causal relationship between a specific microorganism and a specific disease. They are crucial because they provide a rigorous, systematic method for proving the Germ Theory of Disease. The postulates are:

The organism causing the disease can be found in sick individuals but not in healthy ones.
The organism can be isolated from the diseased individual and grown in a pure culture.
The cultured organism must cause the disease when it is introduced into a healthy, susceptible animal.
The organism must be re-isolated from the experimentally infected animal and shown to be the same as the original organism. These postulates remain foundational in microbiology and epidemiology, guiding the identification of disease-causing agents.

Second Year B Pharm Notes, Syllabus, Books, PDF Subjectwise/Topicwise

S Y B Pharm Sem III	S Y B Pharm Sem IV
BP301T Pharmaceutical Organic Chemistry II Theory	BP401T Pharmaceutical Organic Chemistry III Theory
BP302T Physical Pharmaceutics I Theory	BP402T Medicinal Chemistry I Theory
BP303T Pharmaceutical Microbiology Theo	BP403T Physical Pharmaceutics II Theory
BP304T Pharmaceutical Engineering Theory	BP404T Pharmacology I Theory
BP305P Pharmaceutical Organic Chemistry II Practical	BP405T Pharmacognosy I Theory
BP306P Physical Pharmaceutics I Practical	BP406P Medicinal Chemistry I Practical
BP307P Pharmaceutical Microbiology Practical	BP407P Physical Pharmaceutics II Practical
BP308P Pharmaceutical Engineering Practical	BP408P Pharmacology I Practical
	BP409P Pharmacognosy I Practical

History of Microbiology