Definition of Microbiology
- Microbiology is the study of organisms and agents that are too small to be visible with the unaided eye – that is, the study of microorganisms.
- Because objects less than about one millimeter in diameter cannot be seen clearly and must be examined with a microscope, microbiology is concerned primarily with organisms and agents this small and smaller. However, some microorganisms, particularly some eukaryotic microbes, are visible without microscopes. For example, bread molds and filamentous algae are studied by microbiologists, yet are visible to the naked eye, as are the two bacteria Thiomargarita and Epulopiscium.
History of Microbiology
- The term microbiology was given by French chemist Louis Pasteur (1822-95).
- The term microbe was first used by Sedillot (1878).
The Discovery Era
- Robert Hooke, a 17th-century English scientist, was the first to use a lens to observe the smallest unit of tissues which he called “cells”. Soon after, the Dutch amateur biologist Antonio van Leeuwenhoek observed what he called “animalcules” with the use of his homemade microscopes.
- Antonio van Leeuwenhoek (1632-1723) of Delft, Holland (Netherland) was the first person to observe and accurately describe microorganisms (bacteria and protozoa) called “animalcules” in 1675.
Actually, he was a Dutch linen merchant but spent much of his spare time constructing simple microscopes composed of double convex lenses held btw two silver plates. He constructed over 250 small powerful microscopes that could magnify around 50-300 times.
Leeuwenhoek was the first person to produce precise and correct descriptions of bacteria and protozoa using a microscope he made himself. Because of this extraordinary contribution to microbiology, he is considered as the “Father of microbiology”.
Transition Period
- When microorganisms were known to exist, most scientists believed that such life forms could surely rise through spontaneous generation. That is to say, life was thought to spring spontaneously from non-living organic matter or inorganic materials with sufficient nutrients. This concept (called the “theory of spontaneous generation”) was so compelling that it persisted until late into the 19th century.
- The main aspects were to solve the controversy over spontaneous generation which includes experimentations mainly of Francesco Redi, Lazzaro Spallanzani and Louis Pasteur who discarded/disproved the theory of spontaneous generation.
- Francesco Redi (1626-1697): The ancient belief in spontaneous generation was first of all challenged by Redi, an Italian physician, who carried out a series of experiments on decaying meat/flesh and its ability to produce maggots spontaneously.
- Lazzaro Spallanzani (1729-1799): He boiled meat broth (a nutritive broth of vegetables and meat), removed the air from the flask and then sealed the container. Following incubation no growth was observed by him in the flasks. He showed that the heated nutrients could still grow animalcules when exposed to air by simply making a small crack in the neck of the flask.
The Golden Age
- The Golden age of microbiology began with the work of Louis Pasteur and Robert Koch who had their own research institute. More important there was an acceptance of their work by the scientific community throughout the world and a willingness to continue and expand the work. During this period, we see the real beginning of microbiology as a discipline of biology.
- The concept of spontaneous generation was finally put to rest by the French chemist Louis Pasteur in an inspired set of experiments involving a goosenecked flask. When he boiled broth in a flask with a straight neck and left it exposed to air, organisms grew. When he did this with his goose-necked flask, nothing grew. The S-shape of this second flask trapped dust particles from the air, preventing them from reaching the broth. By showing that he could allow only pure air to get into the flask but not the particles in the air, Pasteur proved that it was the organisms in the dust that were growing in the broth.
Thus Pasteur in 1859 finally resolved the controversy of spontaneous generation versus biogenesis and proved that microorganisms are not spontaneously generated from inanimate matter but arise from other microorganisms.He also found that fermentation of fruits and grains, resulting in alcohol, was brought about by microbes and also determined that bacteria were responsible for the spoilage of wine during fermentation. Pasteur in 1862 suggested that mild heating at 62.8°C (145°F) for 30 minutes, rather than boiling was enough to destroy the undesirable organisms without ruining the taste of the product, the process was called Pasteurization. (Pasteurization does not kill spores and vegetative cells)
*Louis Pasteur is known as the “Father of Modern Microbiology”
- John Tyndall (1820-1893) invented the technique of Tyndallization- a sterilization method that kills all forms of microbial life, including the spores and vegetative cells. Tyndallization involves heating the material at 100°C for 20 minutes for three consecutive days with incubation (at 37°C) period in between.
- Around the same time that Pasteur was doing his experiments, a doctor named Robert Koch was working on finding the causes of some very nasty animal diseases (first anthrax and then tuberculosis). He was a German physician and gave the first direct demonstration of the role of bacteria in causing disease.
Koch was the first to discover and isolate Bacillus anthracis (the cause of anthrax) in 1876.
He perfected the technique of isolating bacteria in pure culture. He also introduced the use of solid culture media in 1881 by using gelatin as a solidifying agent. In 1882, Koch discovered Mycobacterium tuberculosis (the cause of tuberculosis)
*Robert Koch is known as the “Father of Bacteriology” - Lord Joseph Lister (1827-1912), a famous English surgeon, developed a system of antiseptic surgery (in 1867) designed to prevent microorganisms from entering wounds by the application of phenol on surgical dressings and at times it was sprayed over the surgical areas. 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. Because of this notable contribution, Joseph Lister is known as the “Father of Antiseptic Surgery”.
- Edward Jenner (1749-1823), an English physician, discovered the first ever vaccine in 1796 against smallpox virus.
- Sir Alexander Fleming discovered the first ever antibiotic penicillin in 1928.
Importance of Microbiology
→ Microbiology is both a basic as well as an applied science.
Modern microbiology expanded tremendously during 20th century resulting into the development of new branches, specialised fields and areas of this discipline! These are bacteriology focusing on bacteria, mycology on fungi, phycology on algae, virology on viruses, and parasitology on protozoa and parasitic worms.
→ The current fields of applied microbiology are as follows:
i) Microbial ecology is concerned with the relationships btw microorganisms and their environment. Microbial ecologists study the role of microbes in recycling of different elements (C, N, S, etc) in soil, atmosphere and water systems.
A field, closely related to microbial ecology is environmental microbiology which deals with the overall impact of the microbial activities on environment. Microbial and environmental microbiologists are employing microorganisms in bioremediation of polluted environments.
ii) Food and dairy microbiology utilise microorganisms to manufacture foods such as bread, milk, butter, cheese, yogurt, pickles, alcohol and beer etc. Food and dairy microbiologists also try to prevent microbial spoilage of food and dairy products and also study the transmission of food-borne diseases such as botulism and salmonellosis.
iii) In industrial microbiology microorganisms are used to make products such as antibiotics, vaccines, steroids, solvents, vitamins, amino acids, enzymes, etc.
Microbes have also been used in biomining to recover precious metals like gold, silver and uranium from low-grade ores.
iv) Agricultural microbiology is concerned with impact of microorganisms on agriculture. Bacteria, cyanobacteria and mycorrhizal fungi, capable of fixing atmospheric nitrogen and solubilising unavailable phosphorous are being used as biofertilizers.
Besides this, microorganisms are also used as biocontrol agents to tackle pathogens, insect pests as well as weeds in agroecosystem.
v) One of the most important and active fields is medical microbiology which deals with the diseases of humans and animals. Medical microbiologists identify the agents responsible for infectious diseases and suggest measures to prevent, eliminate or control them. The precise mechanisms of disease development, pathogenesis is also studied by them.
vi) Immunology: It is the field which is concerned with the various ways by which the immune system protects the body from pathogens and the response of infectious agents. It is one of the fastest growing areas in science. Monoclonal antibodies production and treatment of allergies and autoimmune diseases are the areas of immunology, developing very fast at present.