A History of Microbiology: The Theory of Spontaneous Generation

History of microbiology, Notes, MCQ, PDF, Books

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:

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BP305P Pharmaceutical Organic Chemistry II Practical	BP405T Pharmacognosy I Theory
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