Microbiology is the study of microorganisms too small to be seen with the naked eye. The document introduces key terms and provides a brief history of microbiology, including early theories of spontaneous generation and biogenesis. It describes important early scientists like van Leeuwenhoek, Redi, Spallanzani, and Pasteur and their experiments disproving spontaneous generation. The development of the germ theory of disease by Koch and the classification of microorganisms into domains, kingdoms, and taxa is summarized.

1. INTRODUCTION TO MICROBIOLOGY
Presentation
by
Abura Geoffrey

2. Definitions of key terms used in microbiology
 Microbiology: Is derived from the science (logos) or small (micro) life (bios).
Therefore; microbiology is the study of living things so small that they cannot be
seen with the naked eye.
 Organisms: Any complex thing with properties normally associated with living
things.
 Microorganisms: An organism that is too small to be seen by the unaided eye
(naked eye) such as bacteria.
 Microscope: An optical instrument used for observing small objects.
 Antibiotics: Any substance that can destroy or inhibit the growth of bacteria and
similar microorganisms.
 Antiseptics: Substances that inhibit the growth and reproduction of
microorganism.

3. Introduction to microbiology
 Microbiology often has been defined as the study of organisms and
agents too small to be seen clearly by the unaided eye—that is, the
study of microbes/microorganisms.
 Microbes can exist as single cells, multicellular or as acellular particles.
Subjects are bacteria, viruses, fungi, protozoa and algae
 Microorganisms are ubiquitous in nature and may occur as
 Normal flora(non-pathogenic)
 Pathogenic organisms

4. Con’t
Flaw in definition; some members of these groups,
particularly some of the algae and fungi, are larger and quite
visible to the naked eye
Bread molds and filamentous algae are studied by
microbiologists, yet are visible
Two bacteria that are visible without a microscope,
Thiomargarita and Epulopiscium, also have been discovered

5. Why is microbiology important?
The significance of microbiology is based on both the useful and
harmful effects of its subjects.
Microorganisms are indispensable components of our ecosystem;
They make possible the cycles of carbon, oxygen, nitrogen, and
sulfur that take place in terrestrial and aquatic systems.
They are a source of nutrients at the base of all ecological food
chains.
A lot of production processes and modern biotechnology are
dependent on the activities of microbes e.g.;

6. Importance of microbiology con’t
 Production of bread, cheese, beer
 Manufacture of antibiotics and vaccines
 Production of vitamins(in the gut-vitamin B12, and in industry-various
vitamin supplements), enzymes and many other important products.
Microbial diseases have played a major role in historical events such as
the black death/plague.
Current struggles with killers like HIV/Aids and malaria.
Emerging infections such as hemorrhagic fevers are an eminent threat
to the human population.

7. Subdivision of microbiology
Bacteriology deals about bacteria.
Mycology deals about fungi.
Virology deals about viruses.

8. HISTORY OF MICROORGANISMS
 It is generally believed that microorganisms have existed on earth for several billion years.
However, until a few hundred years ago, no body knew that they existed.
 On the basis that ‘seeing is believing it was only when we had the means to see
microorganisms under a microscope that we could prove their existence.
 Microorganisms had been on the Earth for some 4000 million years, when Antoni van
Leeuwenhoek started out on his pioneering microscope work in 1673.
 Where did these creatures come from?
1. Spontaneous Generation (this was a Myth)
2. Biogenesis theory.

9. Spontaneous Generation
 Until the 2nd half of the 19th century, many scientists and philosophers believed that
some forms of life could arise spontaneously from non-living matter. They called this
hypothetical process spontaneous generation. It was generally believed that;
 Snakes arose from horse hairs in stagnant water.
Mice arose from grain and cheese wrapped in a sweater.
Maggots arose from rotting meat.
Flies arose from fresh and rotting fruit
Mosquitoes arose from stagnant pond water
Locusts arose from green leaves
Termites are generated from rotting wood

10. The Debate over Spontaneous Generation
 The hypothesis [assumption/guessing] that living organisms arise from non-living
matter is called spontaneous generation.
 Francisco Redi (1668): A strong opponent of spontaneous generation.
 In an elegant experiment, the Italian Francesco Redi (1626–1697) showed that
the larvae found on putrefying meat arose from eggs deposited by flies, and not
spontaneously as a result of the decay process.
 To confirm his evidence, He prepared 3 jars each with a piece of meat and
covered with fine net. After some time, there were no maggots in those jars. He
then prepared other 3 open jars with a piece of meat inside them. After some
time, Maggots appeared

12. Conditions Results
3 jars covered with fine net No maggots
3 open jars Maggots appeared
From where did the maggots come?
What was the purpose of the sealed jars?
Redi’s proof was seen as the beginning of the end for the
spontaneous generation theory, but many still clung to the idea,
claiming that while it may not have been true for larger organisms, it
must surely be so for minute creatures such as those demonstrated by
Leeuwenhoek

13. Conditions Results
Nutrient broth heated, then placed in unsealed
flask
Microbial growth
From where did the microbes come?
John Needham (1745): Supported spontaneous generation theory
Needham claimed the "vital force" necessary for
spontaneous generation had been destroyed by the heat &
was kept out of the flasks by the seals.

14. Conditions Results
Nutrient broth placed in flask,
heated, then sealed
No microbial growth
From where did the microbes come?
Lazzaro Spallanzani (1765): Disapproved spontaneous generation theory
Anton Laurent Lavoisier discovered the importance of O2 to life of
organisms.
Spallanzani's observations were criticized on the grounds that there
was not enough O2 in the scaled flasks to support microbial life.

15. Conditions Results
Nutrient broth placed in flask,
heated, not sealed
Microbial growth
Nutrient broth placed in flask,
heated, then sealed.
No microbial growth
Where did the microbes come from?

16. The Theory of Biogenesis
 The issue of spontaneous generation was still unresolved in
1858, when Rudolf Virchow challenged the case for
spontaneous generation with the concept of biogenesis
(that the living organisms arise from preexisting life).
 Arguments about spontaneous generation continued until
1861, when the issue was resolved by Louis Pasteur.

17. Louis Pasteur’s experiment

18. Con’t
 Pasteur was fortunate to have worked with broths prepared from non-
soil or -plant associated substances (e.g., hay).
 Those substances (non-soil or –plant) contain bacteria that can form
endospores, not all bacteria can. Endospores represent a bacterial
durable state and are very difficult to kill.
 John Tyndal (1876) discovered that there exist differences in the ability
of heat to kill different kinds of bacteria-containing cultures.
 Ferdinand Cohn (1876) showed that this difference was due to
endospores and Robert Koch (1877) showed that the bacterium
Bacillus anthracis forms endospores as part of its transmission.

19. Con’t
Aristotle (384-422 BC): The founder of the
theory of spontaneous generation.
He observed spontaneous existence of fishes
from dried ponds, when the pond was filled with
rain.

20. The Golden Age of Microbiology
 The period 1857 - 1914 has been appropriately named the
Golden Age of Microbiology.
 During this period, rapid advances, led to the establishment of
microbiology as a science.
Some of the major events that occurred during the Golden
Age of Microbiology include:
1. Fermentation and Pasteurization
2. The Germ Theory of Disease
3. Vaccination
4. The Birth of Modern Chemotherapy

21. Fermentation and Pasteurization
 Pasteur showed that microbes are responsible for fermentation (conversion of
sugar to alcohol to make beer & wine)
 Bacteria that use alcohol and produce acetic acid spoil wine by turning it to
vinegar (acetic acid)
 Microbial growth is also responsible for spoilage of food
 Pasteur demonstrated that these spoilage bacteria could be killed by heat that
was not hot enough to evaporate the alcohol in wine.
 This application of a high heat for a short time is called pasteurization.

22. History of Microbiology con’t
Man kind has always been affected by diseases
which were originally believed to be visitations by the
gods and meant to punish evil doers.
Hippocrates, father of medicine, observed that ill
health resulted due to changes in air, winds, water,
climate, food, nature of soil and habits of people.

23. Con’t
Varro (117-26 BC) said a theory that: Disease was
caused by animated particles invisible to naked
eye but which were carried in the air through
the mouth and nose into the body.
Fracastorius (1500 BC.) proposed that: The agents
of communicable disease were living germs, that
could be transmitted by direct contact with

24. Con’t
Antony Van Leeuwenhoek (1632-1723 B.C.)- The father
of Microbiology
He observed “animalcules” using simple microscope with
one lens.
Leeuwenhoek was not concerned about the origin of
micro-organism.

25. Major contribution of Louis Pasteur
1. Microbial theory of fermentation
2. Principles and practice of sterilization and
pasteurization
3. Control of diseases of silk worms
4. Development of vaccines against anthrax and
rabies.
5. Discovery of streptococci

26. The germ theory of disease
The complete establishment of the germ theory of disease depended on
the work of a German scientist, Robert Koch (1843-1910).
Koch’s postulates: proof of germ theory of disease
1. The micro-organism should be found in every case of the disease
and under conditions which explain the pathological changes and clinical
features.
2. It should be possible to isolate the causative agent in pure culture
from the lesion.
3. When such pure culture is inoculated into appropriate laboratory
animal, the lesion of the disease should be reproduced.
4. It should be possible to re-isolate the bacterium in pure culture

27. Koch’s postulates

28. Exceptions to Koch’s postulates
1. Many healthy people carry pathogens but do not exhibit symptoms
of the disease.
2. Some microbes are very difficult or impossible to grow in vitro(in
the laboratory) in artificial media. E.g. Treponema pallidum
3. Many species are species specific. E.g. Brucella abortus cause
abortion in animals but no report in humans.
4. Certain diseases develop only when an opportunistic pathogen
invades immunocompromised host.

29. Major achievements of Robert Koch
1. Discovery and use of solid medium in
bacteriology
2. Discovery of causative agents of tuberculosis
and cholera.
3. Koch’s phenomenon
4. Koch’s postulates

30. Basic classification of microorganisms

31. THE MICROBIAL WORLD
Taxonomic classification of organisms
TAXONOMY is the science of organismal classification.
Classification is the assignment of organisms (species)
into an organised scheme of naming .
Ideally these schemes are based on the evolutionary
relationships of the organisms (i.e the more similar the
name, the closer the evolutionary relationships).

32. Con’t
 Thus, classification is concerned with:-
1. The establishment of criteria for identifying organisms &
assignment to groups (what belongs where)
2. The arrangement of organisms into groups of organisms
(e.g. At what level of diversity should a single species be split
in to two or more species?).
3. Consideration of how evolution resulted in the formation
these groups.

33. THE BINOMIAL NOMENCLATURE
Organisms are named using binomial
nomenclature ( viruses are exceptions).
The Binomial nomenclature employs the
names of the two level taxa, genus and
species, to name a species.
 Eg Escherichia coli

34. Con’t
 Binomial nomenclature includes:
i. Genus comes before species (e.g., Escherichia coli)
ii. Genus name is always begins with a capitalized letter (e.g., Escherichia)
iii. Species name is never capitalized (e.g., coli)
iv. Both names are always either italicized or underlined ( e.g Escherichia
coli or Escherichia coli ). Underlining each name is done when hand written
v. The genus name may be used alone, but not the species name (i.e saying or
writing “Escherichia “alone is legitimate while saying or writing “coli” alone is not
accepted)

35. Bacterial species
A bacterial species is defined by the similarities found among
Its members.
 Properties used in defining a bacterial species include:
- Cellular structures,
- Biochemical reactions,
- Chemical composition,
- Genetic characteristics, and
- Immunological features

36. Classification con’t
 The five kingdom system was first proposed in 1969
 The five kingdoms include:
i. Plantae ( the plants)
ii. Fungi ( the fungi)
iii. Animalia ( the animals )
iv. Protista ( the unicellular eukaryotes)
v. Monera ( the prokaryotes)

37. Kingdom of Monera – The Prokaryotes
 Three categories:
- Eubacteria: Are our common, everyday bacteria, some of which are disease -
causing; This is the taxon from which mitochondria originated.
- Cyanobacteria: Are photosynthetic eubacteria, the taxon from which chloroplast
originated,
- Archaeobacteria: Are distinctive in their adaptation to extreme environments
(e.g., very hot, salty, or acidic) though not all archaeobacteria live in extreme
environments.
These distinctions are more phenotypic than they are evolutionary (i.e., a
cyanobacteria is a eubacteria, and neither is an archaebacteria).

38. Kingdom Protista
Protista like Monera consist mostly of unicellular organisms.
Distinctively, however, the members of Kingdom Protista
are all eukaryotic while the members of kingdom Monera
are all prokaryotic.
Some members of protista are multicellular.
However Kingdom protista represents a grab bag,
essentially the place where the species are classified when
they are not classified as either fungi, animals or plants.

39. Kingdom Fungi
 Unlike protists, the eukaryotic fungi are typically non –
aquatic species.
 They traditionally are nutrients absorbers plus have
additional distinctive features.
 They do exist as
- unicellular fungi – the yeasts or
- Multicellular filamentous fungi – the moulds

40. Prokaryotic and eukaryotic cells

41. EUKARYOTIC CELL
- Eu- true
- Karyote- nucleus
 The eukaryotic cell is one that has a true membrane bound nucleus, usually
containing multiple chromosomes, a mitotic apparatus, a well defined endoplasmic
reticulum and mitochondria.
PROKARYOTIC CELL
- Pro- primitive
- Karyote- nucleus
 The prokaryotic cell is one that possesses naked DNA with out associated basic
proteins, divides mitotically by binary fission and bounded by a semi rigid cell wall.

42. Features Prokaryotic cell Eukaryotic cell
Size 1μm 10μm
Nuclear
membrane
Absent Present
Chromosome Single Multiple
Nucleolus Absent Present
Histones Absent Present
Sexual
reproduction
Absent Present
Site of oxidative
phosphorylation
Cell membrane Mitochondria

43. Cytoplasmic
ribosomes
70s 80s
Mitochondria Absent Present
Endoplasmic
reticulum
Absent Present
Lysosomes
Absent
Absent Present
Micro filaments
and tubules
Absent Present

44. Site of
photosynthesis
Cell
membrane Chloroplast
Peptidoglycan Present Absent
Cell membrane
composition
Phospholipids & Proteins Sterols

45. Viruses
A virus is not a cell!
A viral particle consists of a
nucleic acid
molecule(DNA/RNA), enclosed
in a protein coat or caspid.
Unable to replicate outside
living cells

46. Viral classification
 Classification of viruses is not nearly as well developed as the classification of cellular organisms.
 Today viruses tend to be classified by their chemical, morphological and physiological attributes e.g.
 Génome: DNA Viruses or RNA virus, Double stranded DNA viruses or single Stranded DNA viruses
 virion particle: Enveloped virus or non enveloped viruses) etc;
 Binomial nomenclature is not employed to name viruses; instead viruses are named by their
common names e.g.,
 Human Immunodeficiency Virus ( HIV)
 Human Papilloma virus (HPV)
 Ebola virus
 Rabies virus etc.

47. THANK YOU!

48. Coursework assignment
1. Write short notes on the followings;
 General aspects of microbial replication(binary fission,
spore formation)
 Environmental factors needed for bacterial growth
 Nutritional factors needed for microbial growth
 Culture media; classification, types, uses, and quality
 Microbial growth curve; generation time, batch and
continuous culture, pure culture techniques.
 Time New roman,
 Font size 12
 Un limited page numbers