Microbiology is the study of microorganisms. The development of microbiology involved early observations of microbes using microscopes in the 1600s. However, the germ theory of disease was established in the late 1800s by scientists like Pasteur and Koch, who proved microbes cause specific diseases. Major advances included developing techniques to isolate and grow pure cultures of microbes, and discovering antibiotics and vaccines. Today, microbiology remains important for medicine, public health, genetics, and industrial applications like producing antibiotics and other products using microbes.
2. • Microbiology is defined as the science that deals with the study and
significance of microorganisms, such as bacteria, fungi, algae, protozoa,
and viruses.
• The foods that we consume even if sterile, can carry microbial
associations whose composition depends on which organisms gain
access and how they grow, survive and interact in the food over time.
The micro-organisms present in food originate from the natural micro-
flora of the raw material or introduced in the course of
harvesting/slaughter, processing, storage and distribution. The numerical
balance between the various types will be determined by the properties
of the food, its storage environment, properties of the organisms present
and the effects of processing. In spite of the presence of these
microflora, the food is consumed without objection and without adverse
consequences. In some instances, micro-organisms can
• cause spoilage (Soft rot of potato)
• cause foodborne illness (Food poison)
• transform a food’s properties in a beneficial way (fermentation).
3. Development of Microbiology
• Even before microorganisms were seen, some investigators suspected their
existence and responsibility for disease.
• In 1665, the first drawing of a microorganism was published in Robert Hooke’s
Micrographia.
• The first person to publish accurate observations of microorganisms was Antony
van Leeuwenhoek (1632–1723). He was a draper, but spent much of his time
constructing simple microscopes composed of double convex glass lenses held
between two silver plates. His microscopes could magnify around 50 to 300 times.
Leeuwenhoek sent letters of his discoveries to the Royal Society of London. It is
clear from his descriptions that he saw both bacteria and protozoa.
• In the earliest times, people had believed in spontaneous generation—that living
organisms could develop from nonliving matter. Many scientists tried to disprove
the theory but it was Loius Pasteur who finally disproved it. This theory was
challenged by Francesco Redi in 16th century, who carried out a series of
experiments on decaying meat and its ability to produce maggots spontaneously.
He placed meat in three containers: one was uncovered, the second was covered
with paper, and the third was covered with fine gauze. Flies laid their eggs on the
uncovered meat and maggots developed. The other two pieces of meat did not
produce maggots. However, flies were attracted to the gauze-covered container
and laid their eggs on the gauze and produced maggots. Thus the generation of
maggots on decaying meat resulted from the presence of fly eggs, and meat did
not spontaneously generate maggots.
4. • In 1748, John Needham boiled mutton broth and tightly stoppered the flasks.
Many of the flasks became cloudy and contained microorganisms. He thought
organic matter contained a vital force that could confer the properties of life on
nonliving matter.
• A few years later, Lazzaro Spallanzani improved on Needham’s experimental
design by first sealing glass flasks containing water and seeds. If the sealed
flasks were placed in boiling water for 3/4 of an hour, no growth took place as long
as the flasks remained sealed. He proposed that air carried germs to the culture
medium. The supporters of spontaneous generation maintained that heating the
air in sealed flasks destroyed its ability to support life.
• Theodore Schwann (1810–1882) allowed air to pass through a red-hot tube and
then enter a flask containing a sterile nutrient solution. Georg Friedrich Schroder
and Theodor von Dusch allowed air to enter a flask of heat-sterilized medium after
it had passed through sterile cotton wool. The medium remained sterile on both
experiments.
• Finally Louis Pasteur (1822–1895) disproved the theory of spontaneous
generation. He first filtered air through cotton and found minute objects trapped
on it. If a piece of that cotton was placed in sterile medium, microbial growth
occurred. Next he placed nutrient solutions in flasks, heated their necks in a
flame, and drew them out into a variety of curves, while keeping the ends of the
necks open. Pasteur then boiled the solutions for a few minutes and allowed them
to cool. No growth took place even though the contents of the flasks were
exposed to the air. Pasteur pointed out that no growth occurred because dust and
germs had been trapped on the walls of the curved necks. If the necks were
broken, growth commenced immediately.
5. • John Tyndall (1820–1893) demonstrated that dust carried
germs and that if dust was absent, broth remained sterile
even if directly exposed to air. He provided evidence for
the existence of heat-resistant forms of bacteria.
• Ferdinand Cohn (1828–1898) discovered the existence of
heat-resistant bacterial endospores.
6. Golden Age of Microbiology
• A number of disease-causing microbes were discovered, great progress in understanding
microbial metabolism was made, and techniques for isolating and characterizing microbes
were improved. Scientists also identified the role of immunity in preventing disease and
controlling microbes, introduced antiseptic surgery, developed vaccines and antibiotics.
Relationship between Microorganisms and Disease
• The Germ theory of disease:
• Agostino Bassi (1934) and Pasteur (1865) showed a causal relationship between
microorganisms and disease.
• During the 1860s, Joseph Lister developed a system of antiseptic surgery to prevent
microorganisms from entering wounds. Instruments were heat sterilized, and phenol was
used on surgical dressings and at times sprayed over the surgical area.
• In 1876, Robert Koch proved that microorganisms transmit disease, proving that a particular
microorganism causes a particular disease. Koch's postulates states that:
• A specific organism should be found in every case of the disease.
• The organism should be isolated and grown in a pure culture in the laboratory.
• The pure culture when inoculated into a healthy susceptible animal should produce the same disease.
• From the inoculated animal, the microorganism should be isolated in pure culture.
• Angelina, wife of Koch's assistant suggested solidifying broths with agar as an aid to
obtaining pure cultures.
• Koch also developed techniques for isolating organisms and introduced pure cultures. He
isolated Bacillus anthracis (causative agent of anthrax) and Mycobacterium tuberculosis
(causative agent of tuberculosis) and developed tuberculin. His studies on Tuberculosis won
him Nobel prize for philosophy and medicine in 1905. Another important tool developed in
Koch’s laboratory was the petri dish, named after Richard Petri, who devised it. These
developments stimulated progress in all areas of bacteriology.
7. Fermentation and Pasteurization:
• Pasteur found that yeast ferments sugars to alcohols and that bacterium can
oxidize the alcohol to acetic acid. He also showed that microorganisms can grow
either aerobically or anaerobically.
• Heating processes called pasteurization is used to kill bacteria and preserve
alcoholic beverages and milk.
• Pasteur investigated the pèbrine disease of silkworms disrupted silk industry in
Europe. He found that the disease was due to a protozoan parasite. Thus the
disease was controlled by raising caterpillars from eggs produced by healthy
moths.
Virology
• The discovery of viruses and their role in disease was made possible when
Charles Chamberland constructed a porcelain bacterial filter in 1884.
• Dimitri Ivanowski and Martinus Beijerinck studied tobacco mosaic disease. They
found that plant extracts and sap from diseased plants were infectious, even after
being filtered with Chamberland’s filter. Beijerinck proposed that the agent was a
―filterable virus.‖ Later viruses were known to be tiny, acellular infectious agents.
• In 1935, Wendell Stanley crystallized TMV and showed viral particles consisted of
protein and RNA. Viruses were first observed with an Electron Microscope in
1939.
• In 1952, Alfred Hershey and Martha Chase demonstrated that the genetic material
of some viruses is DNA.
• In 1953, James Watson and Francis Crick determined the double helical structure
of DNA.
8. Immunology
• In 1880, Pasteur coined the term vaccine. He discovered that attenuated
(aviruluent) bacteria could be used as a vaccine and developed vaccine
for chicken cholera and rabies.
• Modern vaccines are prepared from living avirulent microorganisms or
killed pathogens, from isolated components of pathogens, and by
recombinant DNA techniques.
• Elie Metchnikoff discovered that some blood leukocytes could engulf
disease-causing bacteria. He called these cells phagocytes and the
process phagocytosis.
Microbial ecology
• Sergei N. Winogradsky (1856-1953) discovered that soil bacteria could
oxidize iron, sulfur and ammonia to obtain energy and many bacteria
incorporate CO2 into organic matter. He also isolated anaerobic nitrogen
fixing soil bacteria and studied the decomposition of cellulose.
• Martinus Beijerinck (1851-1931) isolated aerobic nitrogen fixing
bacterium Azotobacter, a root nodule bacterium also capable of fixing
nitrogen (Rhizobium); and sulfate reducing bacteria. Both of them
developed enrichment culture technique and use of selective media for
growing microorganisms.
9. Chemotherapy:
• There are two types of chemotherapeutic agents: synthetic
drugs and antibiotics.
• In 1910, Elrlich introduced an arsenic containing chemical
called Salvarsan to treat Syphilis.
• In 1929, Alexander Fleming discovered that the fungus
Penicillium produced penicillin, the first antibiotic that could
successfully control bacterial infections. Penicillin has been
used clinically as an antibiotic since the 1940s.
• Waksman developed Streptomycin and other antibiotics
derived from soil organisms.
• Scientists soon found other microorganisms capable of
producing additional antibiotics as well as compounds such as
citric acid, vitamin B12, and monosodium glutamate. At
present, industrial microbiologists use microorganisms to make
products such as antibiotics, vaccines, steroids, alcohols and
other solvents, vitamins, amino acids, and enzymes.
10. Other areas of Microbiology
• Medical microbiology, public health microbiology and
immunology will continue to be areas of intense research.
• Microbial genetics and molecular biology focus on the nature of
genetic information and how it regulates the development and
function of cells and organisms. The use of microorganisms
has been very helpful in understanding gene structure and
function. Microbial genetics play an important role in applied
microbiology to develop techniques that are useful in
agricultural microbiology, industrial microbiology, food and dairy
microbiology, and medicine.
• Genomics and proteomics continue to have a tremendous
impact on microbiology. Microbiologists are facing challenges
to assess the implications of new discoveries and technological
developments. They will need to have a balanced view of both
the positive and the negative long-term impacts of these
developments on society.
11. Reference
• Food Microbiology by Martin R. Adams and Maurice O.
Moss, 3rd e.
• Food Microbiology by William C. Frazier and Dannis C.
Westhoff, 5th e.
• https://www.slideshare.net/SaajidaSultaana/contributions-
of-renowned-scientists-in-microbiology
