Table of Contents
The development of microbiology took place in three distinct historical eras :-
DISCOVERY ERA
In this era, microbial world was explored with the discovery of the microscope. The lens was first invented by Roger Bacone (1267) who developed the lens. Janes & Jansen (1590) developed a crude type of microscope by placing two lenses together without any focusing device.
It was Galileo Galilei (1610) who first prepared a microscope with a true focusing Device; occiale & the name microscope was proposed by Faber (1625).
Discovery of microbial life [Antony van Leeuwenhoek (1677)]
Antony Van Leuwenhoek (1677) first observed the microorganisms (bacteria, yeasts & protozoa) in water, feces, scrapings from his teeth, etc. under his microscope rather than a crude lens system. He was a cloth maker & tailor & his interest in lenses was for the use of these magnifying lenses to examine the quality of fabric. He communicated his findings to the Royal Society of London in the form of hundreds of letters along with his drawings indicating the shape of microbes observed by him. He referred to such tiny organisms as “darkens or animalcules”.
TRANSITION PERIOD
This period started with debates related to the origin of; microbial life & the various findings.
Theory of Spontaneous Generation (Abiogenesis)
According to this theory, all living organisms evolved/ arises spontaneously from non-living matter (Gr. a = without, bios= life, genesis = origin) & was proposed by Thales 624-548 B.C, Anaximander 611-547 B.C., Empedocles, 504-403 B.C., Aristotle, 30 322 B.C. and Socretius 99-55 B.C. They believed that mice, snakes, and frogs could born from moist soil, and maggots could arise from decaying dead bodies. The theory was supported up to 2000 years ago.
Francesco Redi an Italian physician in mid 17th century demonstrated experimentally that the theory of spontaneous generation does not exist. He experimented by taking meat pieces & placing them in jars, some opened & some sealed. Flies entered the jars that were open & laid their eggs on meat that developed into maggots in a few days. In the sealed jars, no maggots appear because flies could not enter.
From these observations, Redi concluded that maggots arise from eggs laid down by flies that entered the jar & can not appear spontaneously. However, his conclusion was not agreed upon by supporters of abiogenesis & who argued that free air which was considered a ‘vital force’ necessary for spontaneous generation/origin was not present in the sealed jars. Redi replaced the seal with muslin cloth through which air (vital force) could easily pass & found the same result. But still, his findings were not accepted and the debate continued.
John Needham (1745) came up with his findings that supported the theory of spontaneous generation. He heated the chicken broth, and corn infusion (nutrient broth) & poured them into covered flasks after cooling the broth. The solution showed the presence of tiny organisms after some time in the covered flasks. Thus he claimed that organisms from the nutrient broth originated spontaneously.
Lazzaro Spallanzani (1767) an Italian naturalist rejected Needham’s claims by his experiments. He boiled the infusion for longer periods & then sealed the flask by melting the glass in the neck; there was no existence of any microbial life.
He demonstrated that the nutrient broth of Needham did not contain microorganisms when heated & explained that microorganisms from the air probably had entered Needham’s solutions after they were boiled. Needham responded that the “vital force” present inside Spallanzani’s sealed flasks had been destroyed by heating & therefore microorganisms did not appear in the absence of vital force & hence the debate continued for the future.
GOLDEN AGE OF MICROBIOLOGY (1860-1910)
The golden age of microbiology began with the work of Louis Pasteur & Robert Koch.
Louis Pasteur (1822-1895)
Founder of Microbiology/Father of Microbiology Pasteur, a French microbiologist performed a series of experiments to prove that the solutions are made free of microbes by boiling & provided with microbe-free air (vital force), there is no existence of any microbial life i.e. no microorganisms originated spontaneously although they were present in free air. In this experiment, he took various types of broths (yeast water, sugar water, urine, etc..) in a long-necked flask, softened the neck of the flask under flame & molded it in the shape of an ‘S’ looking like the neck of a swan.
Therefore this experiment was named the Swan necked flask experiment. The broths were boiled in the flask until steaming & then cooled. The broths after cooling did not decay without any sign of microorganisms after days, weeks & months though opened to free air. Pasteur pointed out that the swan neck of the flasks i.e. walls of curved neck trapped airborne microorganisms before they could reach broth & grow in it.
John Tyndall (1820-1893)
A student of Pasteur conducted experiments to explain that bacteria can exist in two forms: heat liable forms, which could be killed by exposing them to high temperatures, & heat-resistant forms, which could not be killed by continuous boiling of the broth, & grow in the broth after a while.
Tyndall demonstrated that if such broths are subjected to intermittent (discontinuous) boiling-steaming at 100°C on three successive days for 30 minutes, these heat-resistant forms can be killed in broth & no microbial growth will occur thereafter in such broth germ-free) by a process now called Tyndallization’. At first exposure, the vegetative cells are killed but spores may remain. In the interval, spores germinate & grow into the vegetative cell, which is killed during the second exposure. On further exposure, the broth is completely rendered germ-free & no growth occurs for prolonged periods.
Fermentation
It is the process that breaks down carbohydrates (sugars) into alcohols & organic acids. Earlier, people believed that the process of fermentation was a result of spontaneous chemical reactions.
Fermentation is due to microbial activity on a particular substrate. Pasteur studied various types of fermentation & demonstrated that each particular type of fermentation is caused by a specific type of microorganisms, e.g.
- Grape juice + yeast →(incubation) wine
- Grape juice + yeast +Bacteria →(incubation) sour wine
- Grape juice + yeast + Bacteria→(heat incubation) good wine
Pasteur found that during such processes certain undesired microbes grow in ferments which result in undesired products like making the wine sour. To solve this problem Pasteur (1860) suggested that heating could kill such undesirable microbes in ferments, the method now popularly known as Pasteurization (killing microbes by moderate heat application). This proved to be bone for the wine & beer industries. The process is widely employed nowadays in the fermentation & dairy industries.
Contributions of Louis Pasteur (1822-1895)
- 1. Pasteur disproved the theory of spontaneous generation by the Swan-neck experiment.
- 2. He discovered Fermentation of solutions was caused by microorganisms & not by any spontaneous chemical reactions.
- 3. He discovered the existence of life in the absence of oxygen & thus used the terms anaerobic (in absence of oxygen) & aerobic (in presence of oxygen) for the organisms that can live in the absence & presence of oxygen respectively.
- 4. He discovered the process of Pasteurization ( killing Microorganisms by mild heat).
- 5. He developed vaccines against chicken cholera, cholera, anthrax & rabies.
- 6. He discovered silkworm disease pebrine &isolated the causal organism.
- 7. He introduced sterilization techniques & developed steam sterilization, hot air oven & autoclave for sterilization.
- 8. He isolated germs responsible for chicken cholera & rabies.
- 9. He suggested methods to control cross-infection in hospitals (nosocomial infections).
- 10. He introduced attenuated live vaccines for prophylactic use.
- 11. He demonstrated that the causative agent of rabies was too small to be seen through a microscope.
- 12. He discovered Streptococcus & Pneumococcus
THE GERM THEORY OF DISEASE
Earlier, people believed that diseases were caused due to evil spirits or curses from God. With advancements in the discipline of microbiology, it was proved that diseases are caused by microorganisms (Germ theory). Early in 1546, G. Fracastoro stated in his treatise that disease is caused by minute “seed” & spreads from person to person. In 1762, Von Plenciz stated that disease is caused by living organisms & opined that each disease is caused by its organism.
Agostino Bassi (1773-1856) demonstrated that silkworm diseases are due to microbial infections. M.J. Berkeley (1845) demonstrated that the fungus Phytophthora infestans caused famine in Ireland. Johann Schonlein (1793-1864) isolated fungus causing favus.
Oliver Wendell Holmes (1809-1894) suggested that puerperal sepsis (sepsis during childbirth) was due to some germs that are transmitted from mother to child by physicians or nurses.
C.J. Davaine (1812-1882) observed Bacillus causing anthrax & transmitted the disease by inoculating infected blood into healthy animals.
Lord Joseph Lister (1827-1912) demonstrated that wound infections were due to microorganisms. He developed antiseptic surgery to prevent microorganisms from entering wounds by applying phenol while dressing the wounds or surgical areas. He also introduced carbolic acid spray in operation theatres to prevent the growth of microorganisms.
Thus he made an important contribution to antiseptic treatment for the prevention & cure of wound infections & is known as ‘the father of antiseptic surgery.
Robert Koch (1893-1910) (Father of microbial techniques/Father of medical microbiology) proved first time the role of bacteria in causing disease. He isolated anthrax bacillus which causes anthrax. To prove the relationship between the disease & the casual organism he set a few criteria which are popularly known as Koch’s postulates or Koch’s laws.
KOCH’S POSTULATES
Koch (1882) laid down a three-step series/criteria to establish a causal relationship between a causative microbe & a disease. These criteria should be fulfilled before the organism can be confirmed as a real cause of disease & are famously known as Koch’s postulates. These postulates were formulated by Robert Koch & Friedrich Loeffler in 1884 but refined & published by Koch in 1890. The later fourth step was appended by E.F. Smith in 1905. Koch applied these postulates to establish the etiology of anthrax & tuberculosis but they have been generalized to other diseases. The postulates are:-
Postulate I (Association)
The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy animals. In other words, a particular microorganism should be always associated with a particular disease.
Postulate II (Isolation)
The organism must be isolated from the diseased animal & grown in pure culture. Its growth characteristics should be recorded.
Postulate III (Inoculation)
The isolated microorganism should cause the same disease when inoculated into a healthy animal.
Postulate IV (Re-isolation)
The microorganism must be re-isolated from the inoculated (diseased experimental host) host & identified as being identical to the original specific causative agent. Again the re-isolated microorganism must show the same growth characteristics as recorded earlier.
Contributions of Robert Koch
- 1. Koch proved the germ theory of disease (disease is caused by microorganisms).
- 2. He introduced aniline dyes for staining bacteria (staining technique) to see them under a microscope.
- 3. He used agar first time in the solidification of culture media & developed solid culture media.
- 4. He developed methods to obtain a pure culture of microorganisms.
- 5. He laid down postulates to prove the relationship of any microorganism with the disease it causes.
- 6. He discovered the causative agents of anthrax (Bacillus anthracis), tuberculosis (Mycobacterium tuberculosis & cholera (Vibrio cholera).
- 7. He developed a method of heat fixing bacteria during the staining procedure.
- 8. He developed a skin test for the diagnosis of TB (Tuberculin test).
Immunization
Immunization is the artificial induction of immunity by immunizing agents. Lady Mary Montagu first used this practice in smallpox in Asia. Material from the pustule of an infected person was scratched into the skin of the person to be immunized; it resulted in a mild form of smallpox.
E. Jenner (1749-1823) stressed the importance of immunization with cowpox against smallpox. In 1796 he proved that by inoculating pus from cowpox lesions into individuals to be immunized, it protected them against smallpox. This process was known as vaccination (from the Latin word “Vacca” meaning cow). Therefore, the credit for developing the first vaccine for cowpox goes to Jenner. Later on, Louis Pasteur developed attenuated vaccines against chicken cholera & anthrax in 1880 & against rabies in 1885.
Elie Metchnikoff (1845-1916) discovered some leucocytes (WBCs) that engulf the disease-producing bacteria & named the process phagocytosis.
Hens Buchner (1850-1902) demonstrated the presence of bactericidal substances in the blood.
E. Roux & Alexandre Yersin (1853-1935) demonstrated production the of toxins by microorganisms (diphtheria).
E.V. Behring (1854-1917) discovered tetanus antitoxin.
Paul Ehrlich (1854-1915) found that the dye Trypan red was effective against Trypanosome that causes African sleeping sickness & could be used therapeutically. Thus he coined the term Chemotherapy (use of chemicals to kill pathogens) and the dye trypan red was called magic bullet. Subsequently, in association with Sakahiro Hota of Japan, he introduced the drug Salvarsan for the treatment of Syphilis.
Sir Alexander Fleming (1929) discovered the first wonder drug Penicillin from mold Penicillium notatum. Thus, he discovered the first antibiotic (Greek anti = against, bios = life) named penicillin. For commercial production of this antibiotic, P. notatum has been replaced with P. Chrysogenum. Later streptomycin was discovered by S.A. Waksman from Streptomyces griseus in 1944 & received a Noble Prize in 1952 for this discovery which was used in the treatment of tuberculosis.