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Introduction and History of Microbiology

Microbiology consists of the study of the structure, function, categories, and economic significance of microorganisms.


Microbiology consists of the study of the structure, function, categories, and economic significance of microorganisms. Microbiology is an exciting, ever-developing field of science with a wide scope as microbes play an important role in our lives on a daily basis.

An organism or agent too small to be seen by the naked eye is called a microbe, which is the study of their characteristics. The study of microorganisms is the study of their microscopic, living form. Our naked eye cannot see microorganisms because they are smaller than 1 millimeter in diameter. The microorganism can be viewed in a microscope and can exist as a single cell or as a cluster. A microorganism is an organism composed of cellular components such as bacteria, fungi, algae, and protozoa. In addition to viruses, acellular microorganisms are also classified as microorganisms.

Occurrence of micro-organism

Microorganisms, which exist in the air, water and soil, are interesting because they occur everywhere. The microbes inhabit almost every surface of the natural world. Even some microbes can survive in boiling hot springs and ice-covered seas. Microbes outnumber stars in the universe. On Earth, microorganisms make up over 50 percent of the biomass, whereas animals make up only 15 percent. Humans can generally tolerate most microorganisms. The microbes in our bodies are helpful in digesting our food and protecting us from pathogens. As well as maintain the biosphere in a functional state by decomposing dead animals and plants, cycling nutrients, and improving soil health and crop productivity, they are also considered beneficial organisms.

Microbial groups

The morphological, phylogenetic, and physiological characteristics of microorganisms can be classified into six groups.

Bacteria - Prokaryotes, or single-celled organisms, are known as bacteria. BACTERIA reproduce themselves by binary fission and are normally asexual organisms. Their presence dominates the soil, water, and air microbial communities. Many bacteria can even survive in extreme environments, such as those with high temperatures, pH levels, or salinities. They play an important role in nutrient cycling, decomposition of organic matter, and manufacturing of antibiotics, vitamins, and other products used in industry. Other species cause illnesses and food spoilage. For example, Bacillus and Pseudomonas.

Archaea - Archaea are related phylogenetically to bacteria but differ in many ways, most notably by the particular sequences of ribosomal RNA they possess. Extreme environments are home to many archaea. Methanogens, for example, produce methane gas as a byproduct of their metabolism. Methanobacterium is an example.

Algae - An ALGAE is a eukaryote that contains chlorophyll and is capable of photosynthetic activity. Aquatic environments host the most algae. Some of them reproduce sexually, while others reproduce asexually. Food supplements are commonly used to produce them. Agar is usually prepared from them. Examples include gelidium and spirulina.’

Fungi - A fungus is a eukaryote. Their presence in soil is second only to bacteria. From single-celled microscopic yeasts to massive multicellular mushrooms, fungi often come in a variety of sizes and shapes. They produce filamentous mycelium containing individual hyphae that can be sexually or asexually reproduced by spores carried on fruiting structures or by fission, budding, or budding. Yeast, which is responsible for producing alcohol-containing beverages like wine and beer, is a unicellular fungus. Molds, which are multicellular fungi, can produce antibiotics like penicillin in large quantities. Examples include Mucor and Rhizopus.

Protozoa - A protozoan is a unicellular eukaryote without a cell wall that usually moves. Microbial communities are dominated by free-living protozoa, which serve as primary hunters and grazers. These organisms live in a wide variety of environments and some are normally found in animals' digestive tracts, where they help digest complex materials such as cellulose. They can also cause disease if they are parasitic. Examples include amoebas and paramecium.

Viruses - The acellular (noncellular) organisms known as viruses are too small to be seen with the naked eye and can only be detected by electron microscopy. These parasites are all obligate parasites that reproduce only in living cells. Humans, animals, and plants can be infected. Human diseases are caused by most of them. Examples include cauliflower mosaic virus and cucumber mosaic virus.

History of Microbiology

After the discovery of microscopes in the 1600s by pioneer scientists, the field of microbiology developed further and gained importance. It changed the perspective of microorganisms completely in the discipline of microbiology. Conflict between this theory and the theory of spontaneous generation led to the emergence of the theories.

Robert Hooke (1635 – 1600)

Hooke discovered the cell (honeycomb-like structures) in cork cross sections for the first time. Hooke also discovered fungi on microscopic scales. The only microbes he observed were under 30x magnification, which he developed himself.

Anatomy Van Leeuwenhoek (1632 – 1723)

Often referred to as the Father of Microbiology, Leeuwenhoek is revered as a famous scientist. He made lenses and microscopes as a hobby. He was a Dutch merchant. Simple microscopes made of convex glass lenses and held between two silver plates; these microscopes had a magnifying power of 50 to 300. It was he who discovered bacteria and protozoa for the first time. His own teeth were infested with bacteria. His name for these bacteria was animalcules.

The theory of spontaneous generation (abiogenesis)

Several decades after Leeuwenhoek discovered microorganisms, scientists began to investigate their origins. It was assumed that microorganisms were generated spontaneously since organic matter decomposes rapidly outside of the living body. The spontaneous generation theory was supported by Francesco Redi (1626). Wire gauze was placed over the mouth of the flask and the meat was boiled. Due to the odor of meat, flies were attracted to a wire gauze, where they lay eggs, which later mature into maggots. Maggots, he concluded, originated from meat and not from flies. As well as this, Irish priest John Needham (1749) observed microorganisms growing in rotting meat and interpreted it as a spontaneous occurrence.

Theory of biogenesis – La Zaro Spallanzani (1729 – 1799)

An Italian priest named Spallanzani boiled beef broth for an hour before sealing the flasks in order to refute the theory of spontaneous generation and abiotic origin of life. He observed no growth of bacteria, therefore, proving biogenesis to be the origin of life. Whether it is a root, germ cell, or seed, every form of life has its origin in its parents. Louis Pasteur later supported his theory of biogenesis.

Louis Pasteur (1822 – 1895)

He also published numerous books while a professor at Lille University in France. The development of Microbiology as a distinct discipline is credited to his contribution as a "Pioneer of Microbiology". With swan-necked flasks, he discredited the "Theory of spontaneous generation" (Abiogenesis) and proved it to be false. With swan-necked flasks, he discredited the "Theory of spontaneous generation" (Abiogenesis) and proved it to be false. This theory had been discredited by his demonstration that living organisms do not arise from nonliving matter. Using a chemical process called fermentation, he studied the cause of souring of wine and beer and found it to be the growth of microorganisms that produce undesirable alcohol. He found that the wine wasn't ruined when heated to 50-60°C for a few minutes. The method of pasteurizing milk to kill pathogenic microorganisms is now widely used in dairy processing plants.

"Germ theory of disease" is named after him, because he visualized those diseases are caused by microorganisms. His research led him to discover steam sterilizers, autoclaves, and hot air ovens, as well as the importance of sterilization. Cotton wool plugs have also been shown to be highly effective in protecting culture media from contamination from the air. As he distinguished between aerobic and anaerobic bacteria, anaerobic bacteria don't need oxygen for growth.

Using worms free from the protozoan to breed, he showed how to control Pebrine, a silkworm disease caused by a protozoan. During his study of fowls with "chicken cholera", he developed the concept of "attenuation.". After storing the cultures in the laboratory for a while, he found that the animals didn't die as much as when the cultures were fresh. These attenuations are now used as protective vaccines. Pasteur discovered that cattle and sheep are infected by bacteria that cause the anthrax disease. Anthrax organisms were cultivated in sterile yeast water, and he studied whether inoculating healthy animals with these cultures could produce disease. Using an incubation method at 40 to 42°C, he created a live attenuated anthrax vaccine that proved to be useful in preventing anthrax in animals. The swine erysipelas were also his research topics.

A vaccine against rabies (Hydrophobia) was his most important contribution to medicine. Rabbits were injected with the rabies virus serially, and pieces of spinal cord were dried for the vaccine. The boy's life was saved when he tested with him. Pasteur institute's mission was to treat masses of rabies in 1888. The general term "Vaccine", which Jacob Jenner used to describe his cow pox vaccine, arose from Pasteur's general term "Vacca".

John Tyndall (1820 – 1893)

To keep the sterile broth in the chamber, he designed a special chamber to remove dust from the air. There was no evidence of microbial growth in an incubation chamber kept with sterilized broth. This proved that germs were carried in dust and that this was the reason microorganisms grew and not the spontaneous generation. The Tyndall method of sterilization was also developed by him. Also known as intermittent or fractional sterilization, Tyndallization is a form of intermittent or fractional sterilization. Upon tyndallization, the spores and germs will be removed by subsequent steam heating and cooling for 3 days. A 100°C heat kills all vegetative cells. Spore forms are destroyed by subsequent heating once spores germinate.

Robert Koch (1843 – 1912) - Koch’s postulates

Originally a country doctor from Germany, he was appointed Director of the Institute of Infectious Diseases in Berlin, as well as Professor of Hygiene. As the "Father of Practical Bacteriology", he perfected many bacteriological techniques. Upon analysis of the blood of animals who died from anthrax, he discovered rod-shaped organisms. He used inoculated blood to induce the growth of the anthrax organisms on a depression slide by putting infected blood into the aqueous humor of a bullock's eye. The bacteria multiplied and formed spores. A mouse was injected with these spores and the disease was reproduced. Bacillus anthrax can form spores that survive years on earth if certain conditions exist. Twenty generations of mice were passed the anthrax bacteria, originating from the blood of the infected animal, and the bacteria remained pure. This allowed him to study how disease arises.

Techniques for staining were introduced by him. Using an aniline dye, he stained the bacterial films (smears) on glass slides in order to create better contrast under the microscope. It is also referred to as Koch's bacillus (Mycobacterium tuberculosis). Using laboratory animals, Koch injected tubercle bacteria, reproducing the disease, which was in accordance with Koch's postulates. Cholera is caused by Vibrio cholerae, which he discovered. Introducing solid media allowed the development of pure culture techniques. Frau Hesse, the wife of Koch's student, was the first to suggest using agar-agar prepared from dried seaweed (Gelidium Sp.) in making solid bacterial media. It is a totally inert solidifying agent that melts at 90°C, solidifies at 45°C, and has no nutritive value, so it is most suitable for the preparation of culture media. The solid media were used by Koch to isolate a pure culture of bacteria. Bacteriology was revolutionized as a result.

"Old Tuberculin" was discovered by him. Using tubercle bacilli or its protein extract, Koch found that an exaggerated response occurred in Guinea pigs that were already infected with the bacillus, causing localized inflammation. A cell mediated immunity phenomenon; it is called the Koch Phenomenon. Koch's phenomenon is used to test for tuberculin. Erroneously, he believed that tuberculosis can be treated with a protein derived from tubercle bacilli called "Old tuberculin". In line with the teachings of his teacher Henle, Koch conducted a number of experiments in order to demonstrate that a specific microorganism caused a certain disease. Henle and Koch's postulates are commonly referred to as Koch's postulates. They include:
  • In association with the disease, a particular organism should always be identified.
  • Lab cultures should be maintained in isolation and in pure form.
  • An inoculated pure culture should produce symptoms and lesions similar to the disease when injected into a healthy animal.
  • To isolate the organism, the inoculated animal should be exposed to pure culture.
  • Specifically, antibodies to the organism that caused the disease would have to be detected in the patient's serum.

Edward Jenner (1749 – 1823)

In the early 1900s, an English physician named Jenner developed a vaccine against small pox which eventually led to its eradication (Variola). Journalist Jenner observed that dairy workers who had been exposed to cowpox during workplace exposure were immune to small pox. Vaccinia from small pox pustules were injected into man (in 1796) to induce resistance to small pox. James Philipp was the subject of his vaccine test. His term "Vaccine," after Jenner's cow pox vaccine, was used to describe various materials used to induce active immunity. In 1798, Jenner published an essay on the causes and effects of variole vaccination, An inquiry into the cause and effect of variole vaccination.

Joseph Lister (827 – 1912)

A famous nickname given to him is the "Father of Antiseptic Surgery". He taught statistics at the Universities of Glasgow and Edinburgh, and he later taught at King's College, London. Preventing post-operative sepsis was of particular interest to him. He was fascinated by Pasteur's germ theory of disease and hypothesized that sepsis or wound infection could result from bacterial growth originating from the surrounding atmosphere. Through the use of antiseptic techniques, he successfully prevented postoperative sepsis. During surgery or as a spray on the wound, he chose carbolic acid (Phenol). Carbolic acid was applied to wounds as dressings. Consequently, post-operative sepsis, wound inflammation, and suppurative reactions were significantly reduced. Millions of lives were saved from infection-related death. In the future, aseptic surgery would be developed based on Lister's antiseptic surgery. By introducing antiseptic system in 1867, he revolutionized the science of surgery by facing much criticism, but never losing courage.

Iwanowsky (1892)

A Russian botanist who holds a key position in the history of virology is Dmitri Iwanowsky. An agricultural chemist, Adeolf E. Meyer, described in 1866 a disease of tobacco called "Mosaic" in which healthy plants could be infected by the sap of the diseased plants. The disease was caused by a pathogen able to pass through a filter that holds bacteria. Iwanowsky (1892) provided proof of this. After going through the chamberland candle filter, which retained all bacteria, the sap from the infected leaves retained its infectivity when applied to healthy leaves. Dutch Microbiologist Beijerinck demonstrated that the virus could diffuse through agar gel during the "Contagion vivum fluidum" (Virus) era in 1898, and that it was non-corpuscular. Stanley, a British mycologist, obtained the tobacco mosaic infectious agent in crystalline form in 1935.

Metchnikoff (1845 – 1916)

Phytocytosis, the cellular basis of immunity, was discovered by Russian-French biologist Elie Metchnikoff. During a research visit to Italy, he observed that a few of the cells of transparent starfish larvae can engulf and digest foreign proteins. Phagocytes are the creatures that eat cells. The work he did on phagocytosis at the Pasteur Institute in Paris resulted in the discovery that a large proportion of the leucocytes (White blood cells) in human blood are phagocytotic and attack invading bacteria. The infected areas are then inflamed by an increase in leucocytes, followed by swelling, pain, and redness caused by the dead phagocytes forming pus. Since he believed that intestinal bacteria played a key role in the digestion of host cells, and that effectively combating these bacteria would increase human longevity, he spent two decades studying human aging.

Seman E Waksman (1945)

Microbiologist from the United States. Before he discovered Streptomycin antibiotic from soil bacteria, he isolated Thiobacillus thiooxidans, an important discovery. He and his colleagues conducted a systematic search in 1939 for soil organisms that may be able to produce soluble substances needed to control infectious diseases, now known as antibiotics. It took a decade to isolate and characterize ten antibiotics. Actinomycin, streptomycin, and neomycin all had clinical implications in 1940, 1944, and 1949. During his tenure, 18 more antibiotics were discovered.

Alexandar Flemming (1881 – 1955)

His employer was St. Mary's hospital in London, where he worked as a scientist. The lysozyme and penicillin that Flemming discovered were major discoveries. By demonstrating that nasal secretions dissolve or lyse certain kinds of bacteria in 1922, he discovered lysozyme. Later, he showed that lysozyme could be found in many tissue types throughout the body. The antibacterial substance penicillin was discovered by accident by Flemming in 1929 after he accidentally discovered that a fungus called Penicillium notatum produces it. The mold found in Flemming's cultures was later identified as Penicillium notatum. He was cultivating Staphylococci in Petri dishes. There were clear zones around the mold colony where no staphylococci were found. The mold produces antibacterial substances, which Flemming attributes to its action. A fungus called Penicillium notatum was cultured in broth cultures and Flemming filtered the resulting fungal mat to obtain penicillin in dissolved form. The antibacterial activity of the compound was demonstrated in vivo by Howard Florey and Ernst Chain in 1940. The United States was able to produce large quantities of pure penicillin due to their efforts. Physiology and medicine were awarded the Nobel prize for penicillin discovery in 1945. Flemming, Florey, and Chain shared the prize.

Paul Ehrlich (1854 – 1915)

Chemotherapy is a medical procedure pioneered by a German bacteriologist. Having discovered that some tissues had an affinity for chemical drugs, he derived the conclusion that organisms causing disease could be selectively killed. Thus, he developed a synthetic drug, a compound containing arsenic, called "arsphenamine", which killed the syphilis microbe in the body. In an infected animal, Emilius Ehrlich observed that organic arsenicals killed the trypanosomes, but the trypanosomes became tolerant to the drug if smaller doses were administered. So, he sought treatment with "therapia magna sterilans", i.e., the introduction of a chemotherapeutic agent into the bloodstream sufficient to kill the parasite. Furthermore, he observed that a drug would experience certain changes within the body after it had produced the desired effect.

Martinus W. Beijerinck (1851 – 1931)

In parallel with Sergey Winogradsky, he developed the enrichment culture technique for isolating highly specialized microorganisms. During his experiments, Biejerinck cultivated and isolated the bacteria Bacillus radicicola (later dubbed Rhizobium leguminosarum), which fixes nitrogen and causes legume roots to form nodules. The new genus Aerobacter was isolated from Azobacter, which he showed to fix nitrogen. Solvent bacteria that reduce and oxidize Sulphur were isolated. He derived the concept of a contagium vivum fluidum based on his study of tobacco mosaic disease, which he regarded as a living infectious agent in a fluid form (noncellular).

Sergey Winogradsky (1856 – 1953)

In order to isolate Beggiatoa sp., he developed Enrichment Culture Technique. He further explained the nature of chemoautotrophic bacteria, referring to them as anorgoxidants. He also discovered the process of Nitrification and isolated the nitrifying bacterium Nitrobacter and Azotobacter chroococcum, which is a nitrogen fixing bacteria. He is considered the "Father of Soil Microbiology" for his various contributions to soil microbiology. Additionally, he discovered anaerobic nitrogen fixing bacterium Clostridium pasteurianum and Chemolithotrophic nutrition for soil bacteria.
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