1. INTRODUCTION TO MICROBIAL WORLD
Refer Ch. 1 of Text Book ‘Microbiology with Diseases
and Taxanomy’ 2nd ed. By Robert Bauman. Pearson.
2007.
Famous quote of Louis Pasteur (1822-1895):
Three things, WILL, WORK, & SUCCESS, fill
human existence. ‘To will is a great thing, for
Action and Work usually follow Will, and
almost always Work is accompanied by
Success. Will opens the the door to success
both brilliant and happy; Work passes these
doors, and at the end of the journey Success
comes to crown one’s efforts.’
Factors and Questions leading to
the ‘birth’ of microbiology:
• What is the function of nodules at the base
of plants?
• Why does bread turn sour?
• What causes new diseases?
2. Early History
• Greek physician Hippocrates (460 -377
B.C.) –link between environment and
disease
• Greek historian Thucydides (460-404
B.C.) – survivors of plaque who had
contact with victims?
• Antoni van Leeuvwenhoek (1632-1723, a
Dutch tailor, merchant and lens grinder) –
first discovered the bacterial world in 1674.
3. Microbiolgy deals with:
Microbiology often has been dfined as
the study of moicroorganisms
(organisms and agents too small to be
seen by an unaided eye. It deals with:
– Spontaneous generations
– Reasons fermentations occurs
– Cause of diseases
3.1 The discovery of
microorganisms
• The suspected existence and responsibility for disease
by microbes was mentioned by Roman philosopher
Lucretius (98-55B.C.) and the physician Girolamo
Fracastoro (1478-1553).
• Earliest microscopic oberservations, using Galileo’s
microscope, were made on bees and weevils by Italian
Francesco Stelluti between 1625 and 1630.
• First drawing of a microorganism was published in
Robert Hooke’s Micrographia in 1665.
• Accurate oberservations of microorganisms was made
by the amateur microscopist Antony van Leewenhoek
of Delft (1632-1723).
4. How can microbes be
classified?
• Carolus Linnaeus, a Swedish botanist, (17071778)- developed a taxonomic syystem for
naming plants and animals and grouping
organisms (fungi,protozoa,algae, bacteria,
archaea, and small animals) together. Biologists
still use a modification of Linnaeus’ taxonomy
today.
• Technically, viruses are not organisms because
they neither replicate themselves nor caary on
the chemical reactions of living things.
4.1 Salient features/characters of
different microorganisms
All living organisms can be classified as either eukaryotic or
prokaryotic.
Eukaryotes are organisms whose cells contain a nucleus composed of
genetic material surrounded by a distinct membrane.
Prokaryotes are unicellular microbes that lack a true nucleus. Within
these categories, microorganisms are further classified as follows:
Fungi are relatively large microscopic eukaryotes and include molds
and yeasts.
These organisms obtain their food from other organisms and have cell
walls.
Molds are typically multicellular organisms that grow as long filaments,
called hyphae, that intertwine to make up the the body of the the
mold, such as the cottony growths on cheese, bread, and jams.
Pennicillium chrysogenum produces antibiotic pennicillin. They
reproduce by sexual or asexual spores that produce a new
individual without fusing with another cell
Yeasts
• Yeasts are unicellur and typically oval to
round.
• They reproduce asexually by budding, a
process in which a daughter cell grows off
the mother cell. Some also produce sexual
spores (Ascomycetes).
• Saccharomyces cerevisae is used in the
bakery and alcohol industries. Candida
albicans causes yeast infection in women.
Protozoa
• Protozoa are single-celled eukaryotes that are similar to
animals in their nutritional needs and cellular structure.
• Most are capable of locomotion (by pseudopodia or false
foot, cilia, or flagella) and some cause disease.
• Types of protozoa movements: Pseudopodia are
extensions of cell that flow in the direction of travel; Cilia
are short hairlike protusions of a cell the beat
rhythmically to propel the protozoan through its
environment; Flagella are also extensions of a cell, but
are fewer, longer, and more whiplike than cilia. Malaria
causing Plasmodium are nonmotile in mature forms
• They typically live in water, but some inside animal
hosts, where they cause disease.
• Most reproduce asexually, though some are sexual.
Algae
• Algae (Plural of Latin alga, meaning seaweed)are plant-like
eukaryotes that are photosynthetic; that is, they make their own food
from carbon dioxide and water using energy from sunlight. They are
unicellular or multicelluar.
• They are categorised on basis of their pigmentation, their storage
products, and the composition of their cell walls.
• Large algae, commonly called seaweeds and kelps, are common in
the world’s oceans. Chemicals from their gelatinous cell walls are
used as thickeners and emulsifiers in food and cosmetic products,
as well as laboratory media.
• Unicellular algae are common in freshwater ponds, streams, lakes
and oceans. They are food of small aquatic and marine animals and
provide most of the world’s oxygen as a by-product of
photosynthesis. The glasslike cell walls of diatoms are used in
polishing compounds.
Prokaryotes- Bacteria and Archaea
• Bacteria are unicellular prokaryotes whose cell
walls are composed of peptidoglycan(though
some bacteria lack cell walls).
Most bacteria are beneficial acting as micrbial
recyclers for organic waste but some cause
disease.
• Archaea are single-celled prokaryotes whose
cell walls lack peptidoglycan and instead are
composed of other polymers.
They survive in high saline lakes, acid
hotsprings, and oxygen depleted mud at the
bottom of swamps.
Viruses
• Viruses are the smallest of all microbes and
were hidden from microbiologists until the
invention of the electron microscope in 1932.
• All are acellular obligatory parasites causing
many animal and plant diseases and human
epidemics such as small pox, rabies,
influenza,AIDS, the common cold, and some
cancers.
• Technically, viruses are not organisms because
they neither replicate themselves nor carry on
the chemical reactions of living things.
5. The theory of spontaneous
generation (abiogenesis)
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This theory proposes that living organisms can arise from nonliving matter.
It was proposed by Aristotle (384–322 BC) and was widely accepted for
almost 2000 years, until flies-infested meat experiments by Francesco
Redi (1626–1697) challenged it.
In the 18th century, British scientist John T. Needham (1713–1781)
conducted boiling beef gravy and plant infusion experiments in air-tight vials
suggesting that ‘life force’ causes inanimate matter to come to life and
perhaps spontaneous generation of microscopic life was indeed possible,
but in 1799, experiments by Italian scientist Lazzaro Spallanzani (1729–
1799) reported results that contradicted Needham’s findings.
The debate continued until experiments by French scientist Louis Pasteur
(1822–1895) using swan-necked flasks that remained free of microbes
disproved the theory definitively.
The English physicist John Tyndall (1820-1893) dealt a final blow to
spontaneous generation in 1877 by demonstrating that dust did indeed
carry germs and that if dust was absent browth remained sterile even if
directly exposed to air.
5.1 Contribution of theory of
abiogenesis to microbiology
The debate over spontaneous generation led in part to the
development of a generalized scientific method by which questions
are answered through observations of the outcomes of carefully
controlled experiments. It consists of four steps:
1. A group of observations leads a scientist to ask a question about
some phenomenon.
2. The scientist generates a hypothesis—a potential answer to the
question.
3. The scientist designs and conducts an experiment to test the
hypothesis.
4. Based on the observed results of the experiment, the scientist either
accepts, rejects, or modifies the hypothesis
It also contributed to the ‘Golden Age Of Microbiology”
6.The Golden Age of Microbiology
(between late 19th century and
early 20th century)
• Pasteur’s work with swan neck flasks ushered in
the Golden Age of Microbiology.
Within 60 years (1857-1914),
• a number of disease-causing microbes were
discovered,
• great strides in understading microbial
metabolisn were made,
• and techniques for isolating and characterizing
microbes were improved.
6.1 What cause disease?
• Pasteur’s discovery that bacteria are responsible for
spoiling wine led to his hypothesis in 1857 that
microorganisms are also responsible for diseases
• This idea came to be known as the ‘germ theory of
disease’
• Early investigators suspected that cholera, tuberculosis,
and anthrax are each caused by a specific germ, called
a pathogen
• Today we know that some diseases are genetic and
allergic reactiona and enviromental toxins cause others
• Germ theory applies only to infectious diseases.
6.2 Scientists associated with
cause of disease
• Galen (Greek physician, 129-199) accepted the
imbalance of 4 humors (blood, phelgm, yellow bile
[choler], and black bile [melancholy] were associated
with disease
• In the 15th century, Fracastoro and others suggested
that supernatural forces, poisonous vapors called
miasmas, and imbalances among the four humors
thought to be present in the body, produced disease
• Support for the germ theory of disease began in the 19th
century, when Agostino Bassi (1773-1856) first showed
in 1835, that a microorganism could cause a fungal
disease in silkworm. He also suggested that many
diseases were due to microbial infections
6.2 Scientists and cause of disease
• In 1845, M.J. Berkeley proved that the great Potato
Blight of Ireland was caused by a water mold
• In 1853, Heinrich de Bary, showed that smut and rust
fungi caused cereal crop diseases
• Pasteur (1822-1895), who studied fermentation, later
showed that the pebrine disease of silkworm in France
was due to a protozoan parasite
• English surgeon Joseph Lister (1827-1912), developed
a system of antiseptic surgery using phenol to prevent
microorganisms from entering wounds
• The discovery and work on virus in the 19th century was
initiated by Charles Chamberland’s (1851-1908)
porcelain bacterial filter and later by Dimitri Ivanowski
and Maritus Beijerinck who worked on tobacco mosaic
disease.
6.3 Koch’Postulates
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1.
2.
3.
4.
The first demonstration of the role of bacteria causing disease was from
the study of anthrax by the German physician Robert Koch (1843-1910)
who used the criteria proposed by his former teacher Jacob Henle (18091885), to establish the relationship between Bacillus anthracis and
anthrax. He was responsible for advances in staining, culture media &
sterilization and his anthrax work included the following steps:
Koch injected healthy mice with material from diseased animals, and the
mice became ill
After transferring anthrax by inoculation through a series of 20 mice, he
incubated a piece of anthrax-infected spleen containing anthrax bacillus in
beef serum
The bacillus grew, reproduced, and produced endospores
When the isolated bacilli or their spores were injected into mice, anthrax
developed
His criteria for proving the causal relationship between microorganism and
a specific disease are known as Koch Postulates. His study was later
confirmed independenly by Pasteur and his coworkers. His 1884 work on
Mycobacterium tuberculosis as the causal agent of tuberculosis
6.3.1 ETIOLOGY
• Etiology deals with the study of causation of disease. It is
associated with Koch’s Postulates:
1. The suspected causal agent must be found in every
case o the disease and absent from healthy hosts
2. The agent must be isolated and grown outside the
host
3. When the agent is introduced to a healthy, susceptible
host, the host must get infected with the disease
4. The same agent must be reisolated from the diseased
experimental host.
6.4 How to prevent infection and
disease?
• In the 19th century, modern principles of hygiene,such as those
involving sewage and water treatment, personal cleanliness, and pest
control, were not widely practiced.
• In approximately 1848, Viennese physician Ignaz Semmelweis
(1818–1865) hypothesized that “cadaver particles” from the hands of
the medical students caused puerperal fever during child birth, and
required medical students to wash their hands in chlorinated lime
water before attending births
• A few years later, English physician Joseph Lister (1827–1912)
advanced the idea of antisepsis in health care settings, reducing deaths
among his patients by two-thirds with the use of phenol.
• Florence Nightingale (1820–1910), the founder of modern nursing,
introduced antiseptic techniques that saved the lives of innumerable soldiers
during the Crimean War of 1854–1856.
6.4 Prevention of disease
In 1854, observations by the English physician John Snow (1813–
1858) mapping the occurrence of cholera cases in London led to the
foundation of two branches of microbiology: infection controland
epidemiology, the study of the occurrence, distribution, and spread
of disease in humans.
The field of immunology, the study of the body’s specific defenses
against pathogens, began with the experiments of English physician
Edward Jenner (1749–1823), who showed that vaccination with
pus collected from cowpox lesions prevented smallpox
The field of chemotherapy, a branch of medical microbiology in which
chemicals are studied for their potential to destroy pathogenic
microorganisms, began when German microbiologist Paul Ehrlich
(1854–1915) began to search for a “magic bullet” that could kill
microorganisms but remain nontoxic to humans. By 1908, he had
discovered chemicals effective against the agents that cause
sleeping sickness and syphilus
6.3.2 Summary of Golden Age of
Microbiology (1857- 1907)
• Pasteur – development of Industrial microbiology, Pasteurization
(food and beverage technonogy)
• Buchner – Microbial metabolism, Genetics, Genetic engineering
• Koch – Koch’s posthulates – Etiology
• Ivanowski – Virology
• Beijerinck, Winogradsky – Environmental microbiology, Ecological
microbiology
• Gram – Microbial morphology
• Lister, Nightingale – Antiseptic medical techniques, Hospital
microbiology
• Jenner, von Behring, Kitasato – Serology, Immunology
• Ehrich – Chemotheraphy
• Fleming – Pharmaceutical microbiology
6.3.3 What causes fermentation
• The mid-19th century also saw the birth of the field of industrial
microbiology (or biotechnology), in which microbes are intentionally
manipulated to manufacture products.
• Pasteur’s investigations into the cause of fermentation led to the
discovery that yeast can grow with or without oxygen, and that
Bacteria ferment grape juice to produce acids, whereas yeast cells
ferment grape juice to produce alcohol.
• These discoveries suggested a method to prevent the spoilage of
Wine by heating the grape juice just enough to kill contaminating
bacteria, so that it could then be inoculated with yeast.
• Pasteurization, the use of heat to kill pathogens and reduce the
number of spoilage microorganisms in food and beverages, is an
Industrial application widely used today.
6.3.3 Fermentation
In 1897, experiments by the German scientist
Eduard Buchner (1860–1917) demonstrated the
presence of enzymes, cell-produced proteins that
promote chemical reactions such as fermentation.
His work began the field of biochemistry and
the study of metabolism, a term that refers to the
sum of all chemical reactions in an organism.
7. The Future of Microbiology
• Science writer Bernard Dixon talks about the bright future of
microbiology due to:
1. It has a clear vision
2. It has great practical significance
• Microbiologists are called upon to create new drugs and vaccines
using recombinant DNA technology
• Industrial microbiology – food, energy, new antimicrobial agents,
new industrial processes, and bioremedation
• Environmental microbiology- overcoming pollution, toxic wastes, and
protecting food and crops from microbial damage
• Medical microbiology – microbial biofilms for human tissues
• BIGGEST CHALLENGE facing microbiologists will be to assess the
implications of new discoveries and technological developments.
7.1 What will the future hold?
Among the questions microbiologists are working to answer
today are the following:
• What prevents certain life forms from being grown in the
laboratory?
• Can microorganisms be used in ultraminiature
technologies such as computer circuit boards?
• How can an understanding of microbial communities help
us understand communities of larger organisms?
• What can we do at a genetic level to defend against
pathogenic microorganisms?
• How can we reduce the threat of new and re-emerging
infectious diseases?
8. Review assignment questions
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4.
5.
6.
What do you think are the the 5 most important
research areas to pursue in microbiology. Give
reasons for your choice
Describe Pasteur’s work on microbial fermentations
Discuss the contributions of Lister, Pasteur, and Koch
to ‘germ theory of disease’ and to the prevention of
diseases
Describe Koch’s postulates. What is a pure culture?
Why are pure cultures important to Koch’s postulates
What are Koch’s postulates? Why are they important?
Describe Scientific method in your own words. Why is
it important to have a control group?
8. Review questions
7. How did Pasteur and Tyndall finally settle the
‘spontaneous generation’ controversy?
8. Describe and contrast prokaryotic and eukaryotic cells
9. Summarise the ‘Golden Age of microbiology’
10. What is a virus?
11. How would you classify microorganisms?
12. Defend this statement: “The investigations of Antoni
van Leeuwenhoek changed the world forever”
13. Discuss briefly about the procedure and significance of
Gram’s stain.
8.1 How to answer and marks
allocation for the questions
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The students are to form a group of four students per group
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Each group will randomly select and answer one assignment question
•
The answer to the question should be about 500 words making sure that is
no plagiarism of text from internet or textbook. Students will be penalised for
such activity, as they will lose marks.
•
To avoid plagiarism, the students are encouraged to translate the
information from internet or textbook in their own words while citing the
source of reference
•
The answer could be divided into: Introduction (10marks); Contents (50
marks); Conclusion (10 marks); References at least 5 (10 marks); Oral
presentation of about 10-15 min consisting of about 10 ppt slides (10
marks)