INTRODUCTION TO MICROBIOLOGY
Dr Nazia Khan
Assistant professor
College of medicine
Majmaah university
Chapter outline
• INTRODUCTION
• WHAT IS MICROBIOLOGY?
• WHY STUDY MICROBIOLOGY?
• FIRST MICROORGANISMS ON EARTH
• EARLIEST KNOWN INFECTIOUS DISEASES
• PIONEERS IN THE SCIENCE OF MICROBIOLOGY
1. Anton van Leeuwenhoek
2. Louis Pasteur
3. Robert Koch
4. Koch’s Postulates
5. Exceptions to Koch’s Postulates
• CAREERS IN MICROBIOLOGY
LEARNING OBJECTIVES
AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO:
• Define microbiology, pathogen, nonpathogen, and opportunistic pathogen
• Differentiate between acellular microbes and microorganisms
and list several examples of each
• List several reasons why microbes are important (e.g., as a source of
antibiotics)
• Explain the relationship between microbes and infectious diseases
• Differentiate between infectious diseases and microbial intoxications
• Outline some of the contributions of Leeuwenhoek,Pasteur, and Koch to
microbiology
• Differentiate between biogenesis and abiogenesis
• Explain the germ theory of disease
• Outline Koch’s Postulates and cite some circumstances in which they may not
apply
• • Discuss two medically related fields of microbiology
INTRODUCTION
• Biology is the study of living organisms (from bios,
referring to living organisms, and logy, meaning
“the study of”), MICROBIOLOGY includes the study
of certain nonliving entities as well as certain living
organisms.
• Collectively,these nonliving entities and living
organisms are called microbes.
• Micro means very small—anything so small that it
must be viewed with a microscope (an optical
instrument used to observe very small objects).
• Therefore, microbiology can be defined as the study
of microbes
• The various categories of microbes include viruses,
bacteria, archaea, protozoa, and certain types of
algae and fungi.
• Disease-causing microorganisms are
technically known as pathogens (also
referred to as infectious agents)
• Actually, only about 3% of known
microbes are capable of causing disease
(i.e., only about 3% are pathogenic).
Thus, the vast majority of known
microbes are nonpathogens— microbes
that do not cause disease.
• Some nonpathogens are beneficial to us,
whereas others have no effect on us at
all.
• you will learn about both categories—
the microbes that help us (“microbial
allies”) and those that harm us
(“microbial enemies”).
WHY STUDY MICROBIOLOGY
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We have, living on and in our bodies (e.g., on our skin and in our
mouths and intestinal tract), approximately 10 times as many
microbes as the total number of cells (i.e., epithelial cells, nerve
cells, muscle cells, etc.) that make up our bodies (10 trillion cells 10
100 trillion microbes).
It has been estimated that perhaps as many as 500 to 1,000 different
species of microbes live on and in us.
Collectively, these microbes are known as our indigenous microflora
(or indigenous microbiota) and, for the most part, they are of benefit
to us
Some of the microbes that colonize (inhabit) our bodies are known
as opportunistic pathogens (or opportunists).
Although these microbes usually do not cause us any problems, they
have the potential to cause infections if they gain access to a part of
our anatomy where they do not belong. For example E.coli, when a
person run-down, stressed-out, or debilitated (weakened) as a result
3. Microbes are essential for life on this planet as we know it. For
example, some microbes produce oxygen by the process known
as photosynthesis Actually, microbes contribute more oxygen to
our atmosphere than do plants. Thus, organisms that require
oxygen—humans, for algae and cyanobacteria (a group of
photosynthetic bacteria) that produce oxygen.
4. Many microbes are involved in the decomposition of dead
organisms and the waste products of living organisms.
Collectively, they are referred to as decomposers or
saprophytes.
• By definition, a saprophyte is an organism that lives on dead
or decaying organic matter.
• Saprophytes aid in fertilization by returning inorganic nutrients
to the soil. They break down dead and dying organic materials
(plants and animals) into nitrates, phosphates,and other
chemicals necessary for the growth of plants
4. Some microbes are capable of decomposing industrial wastes (oil
spills, for example). The use of microbes in this manner is called
bioremediation.
5. Many microbes are involved in elemental cycles, such as the carbon,
nitrogen, oxygen, sulfur, and phosphorous cycles. In the nitrogen
cycle, certain bacteria convert nitrogen gas in the air to ammonia in
the soil.
• Other soil bacteria then convert the ammonia to nitrites and nitrates.
Still other bacteria convert the nitrogen in nitrates to nitrogen gas,
thus completing the cycle
• Knowledge of these microbes is important to farmers who practice
crop rotation to replenish nutrients in their fields and to gardeners
who keep compost pits as a source of natural fertilizer. In both cases,
dead organic material is broken down into inorganic nutrients (e.g.,
nitrates and phosphates) by microbes.
• The study of the relationships between microbes and the
environment is called microbial ecology.
6. Algae and bacteria serve as food for tiny animals. Then, larger
animals eat the smaller creatures, and so on.
• Thus, microbes serve as important links in food chains
• Microscopic organisms in the ocean, collectively referred to as
plankton serve as the starting point of many food chains. Tiny
marine plants and algae are called phytoplankton, whereas tiny
marine animals are called zooplankton.
7. Some microbes live in the intestinal tracts of animals, where
they aid in the digestion of food and, in some cases, produce
substances that are of value to the host animal. For example,
the E. coli bacteria that live in the human intestinal tract
produce vitamins K and B1, which are absorbed and used by the
human body.
8. Many microbes are essential in various food and
beverage industries, whereas others are used to
produce certain enzymes and chemicals . The use of
living organisms or their derivatives to make or modify
useful products or processes is called biotechnology
9• Some bacteria and fungi produce antibiotics that are
used to treat patients with infectious diseases. By
definition, an antibiotic is a substance produced by a
microbe that is effective in killing or inhibiting the
growth of other microbes. The use of microbes in the
antibiotic industry is an example of biotechnology.
10• Microbes are essential in the field of genetic
engineering. such as insulin, various types of growth
hormones, interferons, and materials for use as vaccine
11. For many years, microbes have been used as “cell
models.”
12. They cause diseases
• Infectious diseases are leading cause of death in the
world and the third leading cause of death in the United
States (after heart disease and cancer)
FIRST MICROORGANISMS
ON EARTH
• infectious diseases of humans and animals have existed for as long as
humans and animals have inhabited the planet. We know that human
pathogens have existed for thousands of years because damage
caused by them has been observed in the bones and internal organs
of mummies and early human fossils.
• Tuberculosis and syphilis, and parasitic worm infections, such as
schistosomiasis, dracunculiasis (guinea worm infection), and
tapeworm infections, have been around for a very long time.
• The earliest known account of a “pestilence” occurred in Egypt about
3180 BC. This may represent the first recorded epidemic, although
words like pestilence and plague were used without definition in early
writings.
• There are early accounts of rabies, anthrax, dysentery, smallpox,
ergotism, botulism, measles, typhoid fever, typhus fever, diphtheria,
and syphilis.
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PIONEERS IN THE SCIENCE
OF MICROBIOLOGY
Bacteria and protozoa were the. first microbes to be observed by
humans. It then took about 200 years before a connection was
established between microbes and infectious diseases.
• Among the most significant events in the early history of
microbiology were
i. the development of microscopes,
ii. bacterial staining procedures,
iii. Techniques that enabled microorganisms to be cultured
(grown) in the laboratory, and steps that could be taken to
prove
that specific microbes were responsible for causing specific
infectious diseases.
• During the past 400 years, many individuals contributed to our
Anton van Leeuwenhoek (1632–1723)
•Because Anton van Leeuwenhoek was the
first person to see live bacteria and
protozoa, he is sometimes referred to as the
“Father of Microbiology,” the “Father of
Bacteriology,” and the “Father of
Protozoology”.
•Leeuwenhoek was not a trained scientist.he
was a fabric merchant, a surveyor, a wine
assayer, and a minor city official in Holland.
•As a hobby, he ground tiny glass lenses,
which he mounted in small metal frames,
thus creating what today are known as
single-lens microscopes or simple
microscopes.
• During his lifetime, he made more than
500 of these microscopes
Louis Pasteur (1822–1895)
•Louis Pasteur , a French chemist, made numerous
contributions to the newly emerging field of
microbiology.
•Below are some of his most significant contributions:
1. While attempting to discover why wine becomes
contaminated with undesirable substances, Pasteur
discovered what occurs during alcoholic fermentation
He also demonstrated that different types of microbes
produce different fermentation products. For example,
yeasts convert the glucose in grapes to ethyl alcohol
(ethanol) by fermentation,
2. The theory of spontaneous generation.
3. He discovered forms of life that could exist in the
absence of oxygen. He introduced the terms “aerobes”
(organisms that require oxygen) and “anaerobes”
(organisms that do not require oxygen).
4. He developed the process called Pasteurization to
kill microbes
Contn……
5. Pasteur discovered the infectious agents that caused the
silkworm diseases that were crippling the silk industry in
France. He also discovered how to prevent such diseases.
6. Pasteur made significant contributions to the germ theory of
disease—the theory that specific microbes cause specific
infectious diseases. For example, anthrax is caused by a
specific bacterium (Bacillus anthracis), whereas tuberculosis
is caused by a different bacterium (Mycobacterium
tuberculosis).
7. Pasteur championed changes in hospital practices to
minimize the spread of disease by pathogens.
8. Pasteur developed vaccines to prevent chicken cholera,
anthrax, and swine erysipelas (a skin disease).
9. Pasteur developed a vaccine to prevent rabies in dogs and
successfully used the vaccine to treat human rabies.
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ROBERT KOCH(1843–1910)
He was a German physician, made numerous contributions
to the science of microbiology. Some of them are :
He made many significant contributions to the germ
theory of disease. For example, he proved that the anthrax
bacillus (B. anthracis), was truly the cause of anthrax. He
developed Koch’s Postulates
Koch discovered that B. anthracis produces spores, capable
of resisting adverse conditions.
Koch developed methods of fixing, staining, and
photographing bacteria.
Koch developed methods of cultivating bacteria on solid
media.He obtained pure cultures of bacteria. The term
pure culture refers to a condition in which only one type
of organism is growing on a solid culture medium or in a
liquid culture medium in the laboratory; no other types of
organisms are present.
He discovered the bacterium (M. tuberculosis) that causes
tuberculosis and the bacterium (Vibrio cholerae) that
causes cholera.
Koch’s work on tuberculin (a protein derived from M.
tuberculosis) ultimately led to the development of a skin
Koch’s Postulates
• During the mid- to late-1800s, Robert Koch and his colleagues established an
experimental procedure to prove that a specific microbe is the cause of a specific
infectious disease. This scientific procedure, published in 1884, became known as
Koch’s Postulates
• Koch’s Postulates :
1. A particular microbe must be found in all cases of the disease and must not be
present in healthy animals or humans.
2. The microbe must be isolated from the diseased animal or human and grown in
pure culture in the laboratory.
3. The same disease must be produced when microbes from the pure culture are
inoculated into healthy susceptible laboratory animals.
4. The same microbe must be recovered from the experimentally infected animals
and grown again in pure culture.
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After completing these steps, the microbe is said to have fulfilled Koch’s
Postulates and has been proven to be the cause of that particular infectious
disease.
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Koch’s Postulates not only helped to prove the germ theory of disease, but also
gave a tremendous boost to the development of microbiology by stressing
laboratory culture and identification of microbes.
Exceptions to Koch’s Postulates
Examples of circumstances in which Koch’s Postulates cannot be
fulfilled :
A. To fulfill Koch’s Postulates, it is necessary to grow (culture) the
pathogen in the laboratory (in vitro) in or on artificial culture
media. However, certain pathogens will not grow on artificial
media. Such pathogens include viruses, rickettsias,chlamydias and
the bacteria that cause leprosy and syphilis.
• Viruses, rickettsias, and chlamydias are called obligate intracellular
pathogens (or obligate intracellular parasites) because they can
only survive and multiply within living host cells.
• Microbes having complex and demanding nutritional requirements
are said to be fastidious (meaning fussy). Although certain
fastidious organisms can be grown in the laboratory by adding
special mixtures of vitamins, amino acids, and other nutrients to
the culture media, others cannot be grown in the laboratory
because no one has discovered what ingredient(s) to add to the
B • To fulfill Koch’s Postulates, it is necessary to infect laboratory
animals with the pathogen being studied.
• However, many pathogens are species-specific, meaning that they
infect only one species of animal. For example, some pathogens
that infect humans will only infect humans. Thus, it is not always
possible to find a laboratory animal that can be infected with a
pathogen that causes human disease. Because human volunteers
are difficult to obtain and ethical reasons limit their use, the
researcher may only be able to observe the changes caused by the
pathogen in human cells that can be grown in the laboratory (called
cell cultures).
C. • Some diseases, called synergistic infections, are caused not by
one particular microbe, but by the combined effects of two or
more different microbes. Examples of such infections include acute
necrotizing ulcerative gingivitis (ANUG; also known as “trench
mouth”) and bacterial vaginosis. It is very difficult to reproduce
such synergistic infections in the laboratory.
D. Another difficulty that is sometimes encountered while
attempting to fulfill Koch’s Postulates is that certain pathogens
become altered when grown in vitro. Some become less
pathogenic, whereas others become nonpathogenic. Thus, they
will no longer infect animals after being cultured on artificial
media.
• It is also important to keep in mind that not all diseases are
caused by microbes. Many diseases, such as rickets and scurvy,
result from dietary deficiencies. Some diseases are inherited
because of an abnormality in the chromosomes, as in sickle cell
anemia.
• Others, such as diabetes, result from malfunction of a body
organ or system.
• Still others, such as cancer of the lungs and skin, are influenced
by environmental factors.
• However, all infectious diseases are caused by microbes, as are
all microbial intoxications.
CAREERS IN MICROBIOLOGY
• A microbiologist is a scientist who studies
microbes
• Bacteriologist
• Protozoologist
• Mycologist
• Virologist
• Medical and Clinical Microbiology
• The field of medical microbiology involves the study of pathogens,
the diseases they cause, and the body’s defenses against disease.
This field is concerned with epidemiology, transmission of
pathogens, disease prevention measures, aseptic techniques,
treatment of infectious diseases, immunology, and the production
of vaccines to protect people and animals against infectious
diseases.
• The complete or almost complete eradication of diseases like
smallpox and polio, the safety of modern surgery, and the
successful treatment of victims of infectious diseases are
attributable to the many technological advances in this field.
• A branch of medical microbiology, called clinical microbiology or
diagnostic microbiology, is concerned with the laboratory
diagnosis of infectious diseases of humans. This is an excellent
career field for individuals with interests in laboratory sciences and
microbiology
MICROSCOPES
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LIGHT MICROSCOPE
BRIGHT FIELD MICROSCOPE
PHASE CONTRAST MICROSCOE
DARK FIELD MICROSCOPE
FLUORESCENCE MICROSCOPE
DIFFERENTIAL INTERFERENCE CONTRAST (DIC)
MICROSCOPE
• ELECTRON MICROSCOPE
• CONFOCAL SCANNING LASER MICROSCOPE
After studying this chapter, answer the
following multiple choice questions.
1. Which of the following individuals is considered to be the “Father
of Microbiology?”
• a. Anton von Leeuwenhoek
• b. Louis Pasteur
• c. Robert Koch
• d. Rudolf Virchow
2. The microbes that usually live on or in a person are collectively
referred to as:
• a. germs.
• b. indigenous microflora.
• c. nonpathogens.
• d. opportunistic pathogens.
3. Microbes that live on dead and decaying organic material are known
as:
• a. indigenous microflora.
• b. parasites.
• c. pathogens.
• d. saprophytes.
4. The study of algae is called:
• a. algaeology.
• b. botany.
• c. mycology.
• d. phycology.
5. The field of parasitology involves the study of which of the following types
of organisms?
• a. arthropods, bacteria, fungi, protozoa, and viruses
• b. arthropods, helminths, and certain protozoa
• c. bacteria, fungi, and protozoa
• d. bacteria, fungi, and viruses
6. . Which of the following microbes are considered obligate intracellular
pathogens?
• a. chlamydias, rickettsias, M. leprae, and T. pallidum
• b. M. leprae and T. pallidum
• c. M. tuberculosis and viruses
• d. rickettsias, chlamydias, and viruses
7. Which of the following statements is true?
• a. Koch developed a rabies vaccine.
• b. Microbes are ubiquitous.
• c. Most microbes are harmful to humans.
• d. Pasteur conducted experiments that proved the theory of abiogenesis.
8. Which of the following are even smaller than viruses?
• a. chlamydias
• b. prions and viroids
• c. rickettsias
• d. cyanobacteria
9.Which of the following individuals introduced the terms
“aerobes” and “anaerobes”?
• a. Anton von Leeuwenhoek
• b. Louis Pasteur
• c. Robert Koch
• d. Rudolf Virchow