Microbiology Dr. Bakthasingh 1
Lec.1 Introduction to Microbiology
Microbiology, the study of microscopic organisms, derived its name from three
Greek words: mikros (“small”), bios (“life”), and logos (“science”). Taken
together they mean the study of microorganisms (MOs) which are very small and
cannot be seen by unaided eye. They are generally 1 millimeter (mm) or less in
diameter.
MOs include organisms such as protozoa, algae, fungi, bacteria and virus (which
are not technically classified as living organisms but do contain genetic material).
MOs are present in vast numbers everywhere on the bodies of animals and
humans, on plant surfaces, in the air, food, water, dust, soil, and even inside the
intestinal canal of all insects, birds, animals and human beings.
The MOs that live inside and on humans (normal microbiota) are estimated to
outnumber human cells by a factor of 10.
Some of these MOs are harmful (disease causing MOs), others benefit by
association with biological activity of the host.
Microbiology research encompasses all aspects of these MOs such as their
behavior, evolution, ecology, biochemistry, and physiology, along with the
pathology of diseases that they cause.
Our goal in this lecture is to introduce you to this amazing group of organisms and to
outline the history of their evolution and discovery.
History of Microbiology
Pre-microbiology
The possibility that microorganisms existed was discussed for many centuries before
their actual discovery in the 17th century.
In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by
transferable seed-like entities that could transmit infection by direct or indirect
contact or even without contact over long distances.
Microorganisms were not described correctly until the 17th century. Why?
The reason for this was that all these early studies lacked the microscope.
The Microscope and Discovery of Microorganisms
Antonie van Leeuwenhoek (1632–1723) was one of the first people to observe
microorganisms, using a microscope of his own design, and made one of the
most important contributions to biology.
, Microbiology Dr. Bakthasingh 2
Robert Hooke was the first to use a microscope to observe living things.
Hooke’s 1665 book, Micrographia, contained descriptions of plant cells. Before
Van Leeuwenhoek’s discovery of microorganisms in 1675, it had been a mystery
why grapes could be turned into wine, milk into cheese, or why food would spoil.
Van Leeuwenhoek did not make the connection between these processes and
microorganisms, but using a microscope, he did establish that there were forms
of life that were not visible to the naked eye. Van Leeuwenhoek’s discovery,
along with subsequent observations by Spallanzani and Pasteur, ended the long-
held belief that life spontaneously appeared from non-living substances during
the process of spoilage.
Lazzaro Spallanzani (1729–1799) found that boiling broth would sterilize it and
kill any microorganisms in it. He also found that new microorganisms could
settle only in a broth if the broth was exposed to the air.
Louis Pasteur (1822–1895) expanded upon Spallanzani’s findings by exposing
boiled broths to the air in vessels that contained a filter to prevent all particles
from passing through to the growth medium. He also did this in vessels with no
filter at all, with air being admitted via a curved tube (swan‐necked flasks) that
prevented dust particles from coming in contact with the broth. By boiling the
broth beforehand, Pasteur ensured that no microorganisms survived within the
broths at the beginning of his experiment. Nothing grew in the broths in the
course of Pasteur’s experiment. This meant that the living organisms that grew in
such broths came from outside, as spores on dust, rather than spontaneously
generated within the broth. Thus, Pasteur dealt the death blow to the theory of
spontaneous generation and supported germ theory instead. He performed
numerous experiments to discover why wine and dairy products became sour, and
he found that bacteria were to blame.
, Microbiology Dr. Bakthasingh 3
In the 1860’s, an English surgeon, Joseph Lister showed the role of MO in the
wound contamination, and developed Lister system which came to be known as
Antiseptic Surgery, which includes the heat sterilization of instruments and the
application of phenol to wound by means of dressings.
Ferdinand Julius Cohn (1828 –1898) was a German biologist. His classification
of bacteria into four groups based on shape (sphericals, short rods, threads, and
spirals) is still in use today.
In 1876, Robert Koch (1843–1910) established that microbes can cause disease.
He found that the blood of cattle who were infected with anthrax always had
large numbers of Bacillus anthracis. Koch found that he could transmit anthrax
from one animal to another by taking a small sample of blood from the infected
animal and injecting it into a healthy one, and this caused the healthy animal to
become sick. He also found that he could grow the bacteria in a nutrient broth,
then inject it into a healthy animal, and cause illness. Based on these
experiments, he devised criteria for establishing a causal link between a microbe
and a disease and these are now known as Koch’s postulates. Although these
postulates cannot be applied in all cases, they do retain historical importance to
the development of scientific thought and are still being used today.
Koch postulates:
1. The suspected causative agent must be found in every case of disease.
2. This MO must be isolated from the infected individual and grown in a culture
with no other types of MO.
3. When inoculation into normal healthy susceptible animal a pure culture of the
agent must be producing the specific disease.
4. The same MO must be isolated from the experimentally infected host.
The steps of Koch's postulates used to relate a specific microorganism to a specific disease.
(a) Microorganisms are observed in a sick animal and (b) cultivated in the lab. (c) The
organisms are injected into a healthy animal, and (d) the animal develops the disease. (e)
The organisms are observed in the sick animal and (f) reisolated in the lab.
Paul Ehrlich (1909) by him chemotherapy was introduced and the modern era of
control treatment began with the use of chemicals that would kill or interfere
with the growth of the disease agent without damaging the infected individual.
Lec.1 Introduction to Microbiology
Microbiology, the study of microscopic organisms, derived its name from three
Greek words: mikros (“small”), bios (“life”), and logos (“science”). Taken
together they mean the study of microorganisms (MOs) which are very small and
cannot be seen by unaided eye. They are generally 1 millimeter (mm) or less in
diameter.
MOs include organisms such as protozoa, algae, fungi, bacteria and virus (which
are not technically classified as living organisms but do contain genetic material).
MOs are present in vast numbers everywhere on the bodies of animals and
humans, on plant surfaces, in the air, food, water, dust, soil, and even inside the
intestinal canal of all insects, birds, animals and human beings.
The MOs that live inside and on humans (normal microbiota) are estimated to
outnumber human cells by a factor of 10.
Some of these MOs are harmful (disease causing MOs), others benefit by
association with biological activity of the host.
Microbiology research encompasses all aspects of these MOs such as their
behavior, evolution, ecology, biochemistry, and physiology, along with the
pathology of diseases that they cause.
Our goal in this lecture is to introduce you to this amazing group of organisms and to
outline the history of their evolution and discovery.
History of Microbiology
Pre-microbiology
The possibility that microorganisms existed was discussed for many centuries before
their actual discovery in the 17th century.
In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by
transferable seed-like entities that could transmit infection by direct or indirect
contact or even without contact over long distances.
Microorganisms were not described correctly until the 17th century. Why?
The reason for this was that all these early studies lacked the microscope.
The Microscope and Discovery of Microorganisms
Antonie van Leeuwenhoek (1632–1723) was one of the first people to observe
microorganisms, using a microscope of his own design, and made one of the
most important contributions to biology.
, Microbiology Dr. Bakthasingh 2
Robert Hooke was the first to use a microscope to observe living things.
Hooke’s 1665 book, Micrographia, contained descriptions of plant cells. Before
Van Leeuwenhoek’s discovery of microorganisms in 1675, it had been a mystery
why grapes could be turned into wine, milk into cheese, or why food would spoil.
Van Leeuwenhoek did not make the connection between these processes and
microorganisms, but using a microscope, he did establish that there were forms
of life that were not visible to the naked eye. Van Leeuwenhoek’s discovery,
along with subsequent observations by Spallanzani and Pasteur, ended the long-
held belief that life spontaneously appeared from non-living substances during
the process of spoilage.
Lazzaro Spallanzani (1729–1799) found that boiling broth would sterilize it and
kill any microorganisms in it. He also found that new microorganisms could
settle only in a broth if the broth was exposed to the air.
Louis Pasteur (1822–1895) expanded upon Spallanzani’s findings by exposing
boiled broths to the air in vessels that contained a filter to prevent all particles
from passing through to the growth medium. He also did this in vessels with no
filter at all, with air being admitted via a curved tube (swan‐necked flasks) that
prevented dust particles from coming in contact with the broth. By boiling the
broth beforehand, Pasteur ensured that no microorganisms survived within the
broths at the beginning of his experiment. Nothing grew in the broths in the
course of Pasteur’s experiment. This meant that the living organisms that grew in
such broths came from outside, as spores on dust, rather than spontaneously
generated within the broth. Thus, Pasteur dealt the death blow to the theory of
spontaneous generation and supported germ theory instead. He performed
numerous experiments to discover why wine and dairy products became sour, and
he found that bacteria were to blame.
, Microbiology Dr. Bakthasingh 3
In the 1860’s, an English surgeon, Joseph Lister showed the role of MO in the
wound contamination, and developed Lister system which came to be known as
Antiseptic Surgery, which includes the heat sterilization of instruments and the
application of phenol to wound by means of dressings.
Ferdinand Julius Cohn (1828 –1898) was a German biologist. His classification
of bacteria into four groups based on shape (sphericals, short rods, threads, and
spirals) is still in use today.
In 1876, Robert Koch (1843–1910) established that microbes can cause disease.
He found that the blood of cattle who were infected with anthrax always had
large numbers of Bacillus anthracis. Koch found that he could transmit anthrax
from one animal to another by taking a small sample of blood from the infected
animal and injecting it into a healthy one, and this caused the healthy animal to
become sick. He also found that he could grow the bacteria in a nutrient broth,
then inject it into a healthy animal, and cause illness. Based on these
experiments, he devised criteria for establishing a causal link between a microbe
and a disease and these are now known as Koch’s postulates. Although these
postulates cannot be applied in all cases, they do retain historical importance to
the development of scientific thought and are still being used today.
Koch postulates:
1. The suspected causative agent must be found in every case of disease.
2. This MO must be isolated from the infected individual and grown in a culture
with no other types of MO.
3. When inoculation into normal healthy susceptible animal a pure culture of the
agent must be producing the specific disease.
4. The same MO must be isolated from the experimentally infected host.
The steps of Koch's postulates used to relate a specific microorganism to a specific disease.
(a) Microorganisms are observed in a sick animal and (b) cultivated in the lab. (c) The
organisms are injected into a healthy animal, and (d) the animal develops the disease. (e)
The organisms are observed in the sick animal and (f) reisolated in the lab.
Paul Ehrlich (1909) by him chemotherapy was introduced and the modern era of
control treatment began with the use of chemicals that would kill or interfere
with the growth of the disease agent without damaging the infected individual.
