- Physics began in ancient times, mathematics even earlier, but the knowledge of tiny living things, their biology, and their impact on human lives have only been around since the late 19th century.
- Until about the 1880s, people still believed that life could form out of thin air and that sickness was caused by sins or bad odors.
- Opinions about why diseases afflicted people differed between cultures and parts of society and the treatments differed as well. Diseases were thought to be caused by
- Bad smells, treated by removing or masking the offending odor
- An imbalance in the humor of the body, treated with bleeding, sweating, and vomiting
- Sins of the soul, treated with prayer and rituals
- Although the concept of contagion was known, it wasn’t attributed to tiny living creatures but to bad odors or spirits, such as the devil.
Varo and Columella in the first century BC postulated that diseases were caused by invisible beings (Animalia minuta) inhaled or ingested.
Fracastorius of Verona (1546) proposed a Contagium vivum as a possible cause of infections disease and Von Plenciz (1762) suggested that each disease was caused by a separate agent.
Discovery of Microbes and the Dawn of Microbiology
- Microbiology is the study of living organisms of microscopic size.
- The term microbiology was given by French chemist Louis Pasteur (1822-95).
- Microbiology is said to have its roots in the great expansion and development of the biological sciences that took place after 1850.
- 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 he called “cells.” Soon after, the Dutch amateur biologist Anton van Leeuwenhoek observed what he called “animalcules” with the use of his homemade microscopes.
- Antonie van Leeuwenhoek (1632-1723) of Delft, Holland (Netherland) was the first person to observe and accurately describe microorganisms (bacteria and protozoa) called ‘animalcules’ (little animals) in 1676.
- Actually he was a Dutch linen merchant but spent much of his spare time constructing simple microscopes composed of double convex lenses held between 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, Antonie van Leeuwenhoek is considered as the “Father of microbiology”.
- Antonie van Leeuwenhoek is also considered to be the father of bacteriology and protozoology (protistology).
- He wrote over 200 letters which were transmitted as a series of letters from 1674-1723 to Royal Society in London during a 50 years period.
- When microorganisms were known to exist, most scientists believed that such simple life forms could surely arise through spontaneous generation. That is to say life was thought to spring spontaneously from mud and lakes or anywhere with sufficient nutrients. This concept was so compelling that it persisted until late into the 19th century.
The main aspects were to solve the controversy over a spontaneous generation which includes experimentations mainly of Francesco Redi, John Needham, Lazzaro Spallanzani, and Nicolas Appert, etc, and to know the disease transmission which mainly includes the work of Ignaz Semmelweis and John Snow.
- 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 and its ability to produce maggots spontaneously.
- John Needham (1713-1781): He was probably the greatest supporter of the theory of spontaneous generation. He proposed that tiny organisms the animalcules arose spontaneously on his mutton gravy. He covered the flasks with cork as done by Redi and even heated some flasks. Still the microbes appeared on mutton broth.
- Lazzaro Spallanzani (1729-1799): He was an Italian Naturalist who attempted to refute Needham’s experiment. He boiled beef broth for longer period, removed the air from the flask and then sealed the container. Followed incubation no growth was observed by him in these flasks. He showed that the heated nutrients could still grow animalcules when exposed to air by simply making a small crack in the neck. Thus Spallanzani disproved the doctrine of spontaneous generation.
- Nicolas Appert followed the idea of Spallanzani’s work. He was a French wine maker who showed that soups and liquids can be preserved by heating them extensively in thick champagine bottles.
- Ignaz Semmelweis and John Snow were the two persons who showed a growing awareness of the mode of disease transmission.
- Two German scholars Schulze (1815-1873) and Theodor Schwan (1810-1882) viewed that air was the source of microbes and sought to prove this by passing air through hot glass tubes or strong chemicals into boiled infusions in flasks. The infusion in both the cases remained free from the microbes.
- George Schroeder and Theodor Von Dusch (1854) were the first to introduce the idea of using cotton plugs for plugging microbial culture tubes.
- Darwin (1859) in his book, ‘Origin of the Species’ showed that the human body could be conceived as a creature susceptible to the laws of nature. He was of the opinion that disease may be a biological phenomenon, rather than any magic.
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 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.
- Pasteur, thus in 1858 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 was introduced into the United States on a commercial basis in 1892. His work led to the development of the germ theory of disease.
- Louis Pasteur is known as the “Father of Modern Microbiology / Father of Bacteriology.
- John Tyndall (1820 – 1893): An English physicist, deal 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 indefinite period even if it was directly exposed to air. He discovered highly resistant bacterial structure, later known as endospore, in the infusion of hay. Prolonged boiling or intermittent heating was necessary to kill these spores, to make the infusion completely sterilized, a process known as Tyndallisation.
- 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 gave the first direct demonstration of the role of bacteria in causing disease. He was a german physician who first of all isolated anthrax bacillus (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 he discovered Mycobacterium tuberculosis. He proposed Koch postulate which were published in 1884 and are the corner stone of the germ theory of diseases and are still in use today to prove the etiology (specific cause) of an infectious disease.
Koch’s four postulates are:
- 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 Louis Pasteur and Robert Koch established the Germ theory of disease. The idea that invisible microorganisms are the cause of disease is called germ theory. This was another of the important contributions of Pasteur to microbiology. It emerged not only from his experiments disproving spontaneous generation but also from his search for the infectious organism (typhoid) that caused the deaths of three of his daughters.
- Fanne Eilshemius Hesse (1850 – 1934) one of Koch’s assistant first proposed the use of agar in culture media. Agar was superior to gelatin because of its higher melting (i.e. 96°C) and solidifying (i.e. 40-45°C) points than gelatin and was not attacked by most bacteria. Koch’s another assistant Richard Petri in 1887 developed the Petri dish (plate), a container used for solid culture media. Thus contribution of Robert Koch, Fannie Hesse and Richard Petri made possible the isolation of pure cultures of microorganisms and directly stimulated progress in all areas of microbiology.
Development in Medicine and Surgery
- Once scientists knew that microbes caused disease, it was only a matter of time before medical practices improved dramatically. Surgery used to be as dangerous as not doing anything at all, but once aseptic (sterile) technique was introduced, recovery rates improved dramatically. Hand washing and quarantine of infected patients reduced the spread of disease and made hospitals into a place to get treatment instead of a place to die.
- Lord Joseph Lister (1827-1912): A famous 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 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. Thus Joseph Lister was the first to introduce aseptic techniques for 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.
Development of Vaccines
- Vaccination was discovered before germ theory, but it wasn’t fully understood until the time of Pasteur. In the late 18th century, milkmaids who contracted the nonlethal cowpox sickness from the cows they were milking were spared in deadly smallpox outbreaks that ravaged England periodically. The physician Edward Jenner used pus from cowpox scabs to vaccinate people against smallpox.
- Edward Jenner (1749-1823) an English physician was the first to prevent small pox. He was impressed by the observation that countryside milk maid who contacted cowpox (Cowpox is a milder disease caused by a virus closely related to small pox) while milking were subsequently immune to small pox. On May 14th , 1796 he proved that inoculating people with pus from cowpox lesions provided protection against small pox. 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. Thus the use of cow pox virus to protect small pox disease in humans became popular replacing the risky technique of immunizing with actual small pox material.
- Jenner’s experimental significance was realized by Pasteur who next applied this principle to the prevention of anthrax and it worked. He called the attenuated cultures vaccines (Vacca = cow) and the process as vaccination. 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 small pox, principle of the preventive treatment of rabies also worked fully which laid the foundation of modern immunization programme against many dreaded diseases like diphtheria, tetanus, pertussis, polio and measles etc.
- Elie Metchnikoff (1845-1916) proposed the phagocytic theory of immunity in 1883. He discovered that some blood leukocytes, white blood cells (WBC) protect against disease by engulfing disease causing bacteria. These cells were called phagocytes and the process phagocytosis. Thus human blood cells also confer immunity, referred to as cellular immunity.
Development of Chemotherapeutics, Antitoxins and Antibiotics
- Emile Roux (1853-1933) and Alexandre Yersin, the two notable French bacteriologists demonstrated the production of toxin in filtrates of broth cultures of the diphtheria organism. Emil von Behring (1854 -1917) and Shibasaburo Kitasato (1852-1931) both colleagues of Robert Koch, in 1890 discovered tetanus (lock jaw) antitoxin. Only about a week after the announcement of the discovery of tetanus antitoxin, Von Behring in 1890 reorted on immunization against diphtheria by diphtheria antitoxin. The discovery of toxin-antitoxin relationship was very important to the development of science of immunology.
- Paul Ehrlich (1854-1915) in 1904 found that the dye Trypan Red was active against the trypanosome that causes African sleeping sickness and could be used therapeutically. This dye with antimicrobial activity was referred to as a ‘magic bullet’. Subsequently in 1910, Ehrlich in collaboration with Sakahiro Hata, a japanese physician, introduced the drug Salvarsan (arsenobenzol) as a treatment for syphilis caused by Treponema pallidum. Ehrlich’s work had laid important foundations for many of the developments to come and the use of Salvarsen marked the beginning of the eni of chemotherapy and the use of chemicals that selectively inhibit or kill pathogens without causing damage to the patient.
- Gerhard Domagk of Germany in 1935 experimented with numerous synthetic dyes and reported that Prontosil, a red dye used for staining leather, was active against pathogenic, Streptococci and Staphylococci in mice even though it had no effect against that same infectious agent in a test tube. In the same year two French scientists Jacques and Therese Trefonel showed that the compound Prontosil was broken down within the body of the animal to sulfanilamide (Sulfa drug) the true active factor. Domagk was awarded nobel prize in 1939 for the discovery of the first sulpha drug.
- The credit for the discovery of this first ‘wonder drug’ penicillin in 1929 goes to Sir Alexander Fleming of England, a Scottish physician and bacteriologist. Fleming had been actually interested in searching something that would kill pathogens ever since working on wound infections during the first world war (1914-1918).
- Antibiotics were discovered completely by accident in the 1920s, when a solid culture in a Petri dish (called a plate) of bacteria was left to sit around longer than usual. As will happen with any food source left sitting around, it became moldy, growing a patch of fuzzy fungus. The colonies in the area around the fungal colony were smaller in size and seemed to be growing poorly compared to the bacteria on the rest of the plate. The compound found to be responsible for this antibacterial action was named penicillin. The first antibiotic, penicillin was later used to treat people suffering from a variety of bacterial infections and to prevent bacterial infection in burn victims, among many other applications. In this way, Sir Alexander Fleming in 1929 discovered the first antibiotic penicillin.
- Waksman at the Rutgers university, USA discovered another antibiotic, streptomycin produced by two strains of actinomycete, Streptomyces griseus in 1944. Waksman received the noble prize in 1952 for his discovery of Streptomycin used in the treatment of tuberculosis, a bacterial disease caused by Mycobacterium tuberculosis that had been discovered by Robert Koch in 1882. By 1950, three other microorganism were identified that produced antibiotics, such as chloramphenicol (Chloromycetin) from Streptomyces venezuelae by Dr. Paul R. Burkholder in 1947, Aureomycin from S. aureofaciens by Dr. B.M. Dugger in 1948; and Terramycin from S. rimosus by Finlay, Hobby and collaborators in 1950.
- A dramatic turn in microbiology research was signaled by the death of Robert Koch in 1910 and advent of World war I. The Pasteur Institute was closed, and the German laboratories converted for production of blood components used to treat war infections. Thus came to an end what many have called the Golden Age of Microbiology.
In 20th Century: Era of Molecular Biology
- By the end of 1900, science of microbiology grew up to the adolescence stage and had come to its own as a branch of the more inclusive field of biology.
- In the later years the microorganism were picked up as ideal tools to study various life processes and thus an independent discipline of microbiology, molecular biology was born.
- The relative simplicity of the microorganism, their short life span and the genetic homogeneity provided an authentic simulated model to understand the physiological, biochemical and genetical intricacies of the living organisms.
- The field of molecular biology made great strides in understanding the genetic code, how DNA is regulated, and how RNA is translated into proteins. Until this point, research was focused mainly on plant and animal cells, which are much more complex than bacterial cells. When researchers switched to studying these processes in bacteria, many of the secrets of genes and enzymes started to reveal themselves.
Important Contributors in Microbiology
Louis Pasteur is known as the “Father of Modern Microbiology / Father of Bacteriology. He has many contributions to microbiology:
- He has proposed the principles of fermentation for the preservation of food.
- He introduced sterilization techniques and developed steam sterilizers, hot air oven, and autoclave.
- He described the method of pasteurization of milk.
- He had also contributed for designing the vaccines against several diseases such as anthrax, fowl cholera, and rabies
- He disproved the theory of spontaneous generation of disease and postulated the ‘germ theory of disease’. He stated that disease cannot be caused by bad air or vapor, but it is produced by the microorganisms present in the air.
- Liquid media concept- He used nutrient broth to grow microorganisms.
- He was the founder of the Pasteur Institute, Paris.
Louis Pasteur proposed:
• Principles of fermentation
• Pasteurization of milk
• Sterilization techniques
• The germ theory of disease
Robert Koch provided remarkable contributions to the field of microbiology:
- He used solid media for the culture of bacteria-Eilshemius Hesse, the wife of Walther Hesse, one of Koch’s assistants had suggested the use of agar as a solidifying agent.
- He also introduced methods for isolation of bacteria in pure culture.
- Described the hanging drop method for testing motility.
- Discovered bacteria such as the anthrax bacilli, tubercle bacilli, and cholera bacilli.
- Introduced staining techniques by using aniline dye.
- Koch’s phenomenon: Robert Koch observed that guinea pigs already infected with tubercle bacillus developed a hypersensitivity reaction when injected with tubercle bacilli or its protein. This reaction is called Koch’s phenomenon.
According to Koch’s postulates, a microorganism can be accepted as the causative agent of an infectious disease only if the following conditions are fulfilled:
i. The microorganism should be constantly associated with the lesions of the disease.
ii. It should be possible to isolate the organism in pure culture from the lesions of the disease.
iii. The same disease must result when the isolated microorganism is inoculated into a suitable laboratory animal.
iv. It should be possible to re-isolate the organism in pure culture from the lesions produced in the experimental animals.
An additional fifth criterion was introduced subsequently which states that antibodies to the causative organism should be demonstrable in the patient’s serum.
Exceptions to Koch’s postulates: It is observed that it is not always possible to apply these postulates to study all human diseases.
There are some bacteria that do not satisfy all the four criteria of Koch’s postulates. Those organisms are:
• Mycobacterium leprae and Treponema pallidum: They cannot be grown in vitro; however can be maintained in animals.
• Neisseria gonorrhoeae: There is no animal model; however, bacteria can be grown in vitro.
Molecular Koch’s postulates: It was a modification of Koch’s postulates (by Stanley Falkow). He stated that the gene (coding for virulence) of a microorganism should satisfy all the criteria of Koch’s postulates rather than the microorganism itself.
- He was the first to report the acid-fast nature of tubercle bacillus.
- He developed techniques to stain tissues and blood cells.
- He proposed a toxin-antitoxin interaction called an Ehrlich phenomenon and also introduced methods of standardizing toxin and antitoxin
- He proposed the ‘side-chain theory for antibody production’.
- He discovered ‘salvarsan’, an arsenical compound (magic bullet) for treatment of syphilis, hence Paul Ehrlich is known as the father of chemotherapy.
- The bacteria ‘Ehrlichia’was named after him.
Other Important Contributors in Microbiology
1. Antonie Philips van Leeuwenhoek: Discovered single-lens microscope and named organisms as ‘Little animalcules’.
2. Edward Jenner: Developed the first vaccine of the world, the smallpox vaccine by using the cowpox virus.
3. Joseph Lister: Joseph Lister is considered to be the father of antiseptic surgery. He used carbolic acid during surgery.
4. Hans Christian Gram: He developed a ‘Gram stain’.
5. Ernst Ruska: He was the founder of the electron microscope.
6. Alexander Fleming: He discovered the antibiotic penicillin.
7. Elie Metchnikoff: He described phagocytosis and termed phagocytes.
8. Kleinberger: He described the existence of L forms of bacteria.
9. Barbara McClintock: She described transposons.
10. Walter Gilbert and Frederick Sanger: were the first to develop (1977) the method of DNA sequencing.
11. Karry B Mullis: Discovered polymerase chain reaction (PCR).
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