Medical microbiology is a branch of medicine that deals with the study of microorganisms and their role in human health and diseases. It also concerns with the diagnosis, treatment and prevention of various infectious diseases.
There are four kinds of microorganisms that cause
infectious disease: bacteria, fungi, parasites and viruses.
The branches of medical microbiology are as follows:
• General microbiology: Study of general properties of microorganisms, such as bacterial morphology, sterilization and disinfection, culture identification. methods, bacterial genetics, etc.
• Immunology: The study of the immune system
• Bacteriology: The study of bacteria
• Virology: The study of viruses
• Mycology: The study of fungi
• Parasilology: The study of parasites; it has two arms
Protozoology: The study of protozoa. Helmimhology: The study of helminths.
CONTRIBUTORS IN MICROBIOLOGY:
Antonie Philips van Leeuwenhoek (1676)
He was the first scientist who observed bacteria and
other microorganisms, using a single-lens microscope constructed by
him and he named those small organisms as 'Little animalcules'(Fig. 1.1A).
Edward Jenner
Edward Jenner 1796, developed the first vaccine of
the world, the smallpox vaccine. He used the cowpox virus (Variolae vaccinae) to immunize children against smallpox from which the term
'vaccine' has been derived. The same principles are still used today for
developing vaccines.
Louis Pasteur
Microbiology developed as a scientific discipline from the
era of Louis Pasteur (1822- 1895). He is also known as father of
microbiology. He was a professor of chemistry in France. His studies on
fermentation led him to take interest to work in microbiology (Fig.
1.1B). His contributions to microbiology are as follows:
• He had proposed the principles of fermentation
for preservation of food.
• He introduced the sterilization techniques
and developed steam sterilizer, hot air oven and autoclave.
• He described the method of pasteurization of milk.
• He had also contributed for the vaccine
development 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 it.
• Liquid media concept: He used nutrient broth to
grow microorganism.
• He was the founder of the Pasteur Institute, Paris.
Joseph
Lister
Joseph Lister (1867) is considered to be the father of antiseptic surgery. He had observed that postoperative infections were greatly reduced by using disinfectants such as diluted carbolic acid during surgery to sterilize the instruments and to clean the wounds.
Robert Koch
Robert Koch provided remarkable contributions to the field of
microbiology. He was a German general practitioner (1843- 1910)
(Fig.1.1 C).
His contributions are
as follows:
• He introduced solid media for culture of bacteria, Eilshemius Hesse, the wife of, one of Koch's
assistants had
suggested the use of agar as solidifying agents.
• He also introduced methods for isolation of bacteria in pure culture.
• He described hanging drop method
for testing motility.
• He discovered bacteria such as the
anthrax bacilli, tubercle bacilli and cholera bacilli.
• He 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. Since then, this observation was called as Koch's phenomenon.
• Koch's postulates: Robert Koch had postulated that a microorganism can be accepted as the causative agent of an infectious disease only if four criteria are fulfilled.
These criteria are as
follows:
1.The microorganism should be constantly associated with the lesions of the disease.
2. It should be possible to isolate the organism in pure culture from the
lesions of the disease.
3.The same disease must result when the isolated
microorganism is inoculated into a suitable laboratory animal.
4. 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 antibody to the causative organism should be demonstrable in the patient's serum.
Exceptions to Koch's postulates: It is observed the it is
not always possible
to apply these postulates to study all the 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, they can be maintained in experimental animals.
• Neisseria gonorrhoeae: There is no animal model;
however, it can be grown in vitro.
Molecular Koch's Postulates:
It was a
modification
of Koch's postulates formulated by the
microbiologist Stanley Falkow (1988).
He stated that gene (coding for virulence) of a pathogenic microorganism that
contributes
to the
disease should satisfy all the
criteria of Koch's postulates rather than
the microorganism itself.
• The virulence trait under study should be associated much more with pathogenic strains of the species than with non-pathogenic strains.
• Inactivation of the gene associated with
the suspected virulence trait should substantially decrease
pathogenicity.
• Replacement of the mutated gene with the normal wild type gene should fully restore pathogenicity.
• The gene should be expressed at some point during the infection and disease process.
• Antibodies or immune system cells directed against the gene products should protect the host.
Paul Ehrlich
Paul Ehrlich (1854- 1915) was a German scientist and is also known as father of chemotherapy (Fig. 1.1D).
His contributions are as follows:
• 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
Ehrlich phenomenon and also introduced methods of standardising toxin and antitoxin.
• He proposed the 'side chain theory for antibody production'.
• Chemotherapy: He discovered salvarsan, an arsenical compound (also called as the 'magic bullet') as the first effective medicinal treatment for syphilis, thereby intiating and also naming the concept of chemotherapy.
• The bacteria 'Ehrlichia' was named after him.
• In 1908,
he received the Nobel prize in Physiology or Medicine for his contributions to
immunology.
• He was the founder and first director of what is known now as the Paul Ehrlich Institute, Germany.
Other Important Contributors:
• Hans Christian Gram (in 1884): He developed a method of staining bacteria which was named as 'Gram stain' to make them more visible and differentiable under a microscope.
• Charles Chamberland: He is one of Pasteur's associates, constructed a porcelain bacterial filler in 1884 by which the discovery of viruses and their role in disease was made possible. The first viral pathogen to be studied was the tobacco mosaic virus.
• Ernst Ruska: He was the founder of electron microscope (1931).
• Alexander Fleming (in 1929): He discovered the most commonly used antibiotic
of the last century i.e. penicillin.
• Goodpasture: He
described thr viral culture technique in chick embryo.
• Lady Mary Worlley Monlagu: Introduced variolation for immunizing against smallpox.
• Elie Melchnikoff: He described phagocytosis and termed phagocytes.
• Emmy Klieneberger (1941): She described the existence of L
forms of bacteria.
• Barbara McClinlock: She described the mobile genetic elements in bacteria called transposons.
• Waller Gilbert and Frederick Sanger were the first to develop
(1977) the method of DNA
sequencing.
• Karry B Mullis: Discovered polymerase
chain reaction(PCR) and was awarded Noble prize in
1993.
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