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First semester
 Topics Covered
 Scope of Microbiology
 Importance of Microorganisms
 Characteristics of Microorganisms
 History of Microbiology
 Taxonomy
Infectious diseases have been known for thousands of years, although accurate
information on their etiology has only been available for about a century.
In the medical teachings of Hippocrates, the cause of infections occurring
frequently in a certain locality or during a certain period (epidemics) was sought in
“changes” in the air according to the theory of miasmas.
This concept, still reflected in terms such as “swamp fever” or “malaria,” was the
predominant academic opinion until the end of the 19th century, despite the fact
that the Dutch cloth merchant A. van Leeuwenhoek had seen and described
bacteria as early as the 17th century, using a microscope he built himself with a
single Convex lens and a very short focal length.
At the time, general acceptance of the notion of “spontaneous generation”—
creation of life from dead organic material—stood in the way of implicating the
bacteria found in the corpses of infection victims as the cause of the deadly
It was not until Pasteur disproved the doctrine of spontaneous generation in the
second half of the 19th century that a new way of thinking became possible. By the
end of that century, microorganisms had been identified as the causal agents in
many familiar diseases by applying the Henle-Koch Infectious diseases are caused
by subcellular infectious entities
(prions, viruses), prokaryotic bacteria, eukaryotic fungi and protozoans, metazoan
animals, such as parasitic worms (helminthes), and some arthropods.
Definitive proof that one of these factors is the cause of a given infection is
demonstrated by fulfillment of the three Henle-Koch postulates. Postulates
formulated by R. Koch in 1890.
 study of organisms too small to be seen by the naked eye.
 It means micro-organism ology science, it is a branch of science
deals with study of microorganism including (Bacteria, viruses ,
yeast, mould , chlamydiae, helminthes ,protozoa , prion(infection
proteins) ,Arthropod ,and Rickettsia.
 Laius Pasteur 1820-1890 –France chemist
 Robert Kock
1840-1910 -Germany doctor, he discovered
Tuberculosis in 1882 and cholera 1883.
 The relationship between Virus, yeast, mould, and bacteria, the
yeast and mould is large while a bacterium is intermediate but a
virus is the smallest.
Branches of Microbiology:
 Bacteriology
study of bacteria
 Mycology
study of fungi and yeast
 Virology
study of viruses
 Parasitology
study of parasitic protozoans and
study of the humoral and cellular
immune response to disease agents and allergens
 Specializations in Microbiology:
 Epidemiology and Public Health Microbiology
distribution and spread of diseases and their control and prevention
 Food Microbiology
use of microbes in the production of food products and drinks
 Agricultural and Veterinary Microbiology
use of microbes to increase crop and livestock yield and control of
plant pests and animal diseases
 Environmental Microbiology
study of the beneficial and harmful effects of microbes on the
Importance of Microbiology:
 First bacteria
 Photosynthesis and decomposition
 Human use of microorganisms
 Infectious diseases
Microbes or Microorganisms
 commonly referred to as “germs” or “bugs”
 include bacteria, viruses, fungi, algae, protozoa and helminths.
 Prions (“infectious proteins”) are recent addition.
 Microorganism is all the microscopic living.
1. Photosynthetic Microbes:
 Microbes are involved in photosynthesis and accounts for
>50% of earth’s oxygen.
 Also involved in decomposition and nutrient recycling.
2. Beneficial Uses of Microbes
Extraction of copper from ore.
Synthesis of drugs, hormones and enzymes.
Bioremediation is the use of microbes to degrade organic
matter in sewage and detoxify pollutants such as oil spills.
3. Modern Uses of Microbes:
Biotechnology, the use of microbes as miniature
biochemical factories to produce food and chemicals is
centuries old.
Genetic engineering makes use of molecular biology and
recombinant DNA techniques as new tools for
iii. Gene therapy replaces missing or defective genes in
human cells through genetic engineering.
Genetically modified bacteria are used to protect crops
Early theories of the causes of diseases:
Theoretical: show the diseases are punishment of bad people.
Miasmatic theory (Hippo crates):
The disease is waves appear from earth, moon, and stars.
Germ theory ( Erectors) 1546
Is the transmission of the disease from person to another called
(contagious vivum).
Bacteria is unicellular of primitive structure.
Bacteria composes with animal and plant cells.
Plant kingdom
Bacteria , rickettsia and virus
(without cells)
Yeast, mould, Enmycetes
(Rickettsia and viruses)
Hoekel 1986 put the microorganism in the animal kingdom, king-protists.
1- Higher protists (Eukaryotes):
Like protozoa, fungi, yeast, and mould.
2- Lower protists (prokaryotes):
Microbial Taxonomy
General Characteristics:
 Prokaryotes
no nucleus and organelles
 Eukaryotes
membrane bound nucleus
and organelles
 A cellular agents genomes contain either DNA or RNA; newer
agent is proteinaceous
Comparative cellular structures of microbes
The Microbes
Brief History of Microbiology:
1- The Microscope
Microbes were first observed by Antonie van Leeuwenhoek using a
simple microscope (ca. 1673) . Reported his “animalcules” to the Royal
Society of London
Spores and Sterilization
John Tyndall showed that some microbes in dust and air were
resistant to heat.
Ferdinand Cohn discovered and described endospores
Term “sterile” was introduced to mean the complete removal of all life
forms including endospores
3- Spontaneous Generation
Spontaneous Generation” was an early belief that living things can
arise from vital forces present in nonliving and decaying matter.(Ex:
maggots from meat or mushrooms from rotting wood).
The alternative hypothesis that living organisms can arise only from
preexisting life forms is called “Biogenesis”
4- Aseptic Technique:
Louis Pasteur put an end to Abiogenesis debate with his
Goose Neck Flask Experiment
He is the father of Microbiology
Louis Pasteur:
Showed microbes caused fermentation
Studied spoilage and introduced “Pasteurization” to prevent it
Used cotton plugs in his cultures to prevent air borne contamination,
devised Aseptic Technique.
Antiseptics and Hand Washing:
1860s - Joseph Lister used, carbolic acid, a chemical antiseptic to
prevent surgical wound infections.
Ignaz Semmelweis, a Hungarian physician introduced hand washing as
a means of preventing transfer of puerpueral sepsis in obstetrical
5- Germ Theory of Disease:
1876 - Robert Koch provided proof that a bacterium causes anthrax
using experimental steps now called the Koch’s Postulates
He was the first to use agar as solid culture medium in bacteriology.
Koch’s Postulates:
The microbe must always be present in every case of the disease
It must be isolated in pure culture on artificial media
When inoculated into healthy animal host it should produce the same
It must be isolated from the diseased animal again
Infection and Disease:
the entry of a microbe into the host.
infection followed by the appearance of
signs and symptoms.
 Pathogen
an infectious or disease agent or Subcellular Infectious
a microbe that lives on dead or decaying organic matter.
Opportunistic pathogen
is a microbe that cause disease in immunocompromised hosts or when
the normal microbiota is altered.
Prions: (proteinaceous infectious particles). The evidence indicates that
prions are protein molecules that cause degenerative central nervous
system (CNS) diseases such as Creutzfeldt-Jakob disease, kuru,
scrapie in sheep, and bovine spongiform encephalopathy (BSE)
(general term: transmissible spongiform encephalopathies [TSE]).
Viruses: Ultramicroscopic, obligate intracellular parasites that:
Contain only one type of nucleic acid, either DNA or RNA; possess no
enzymatic energy-producing system and no protein-synthesizing.
Apparatus and force infected host cells to synthesize virus particles.
Classic bacteria.
These organisms reproduce asexually by binary transverse fission. They
do not possess the nucleus typical of eukaryote. The cell walls of these
organisms are rigid (with some exceptions, e.g., the mycoplasma).
These organisms are obligate intracellular parasites that are able to
reproduce in certain human cells only and are found in two stages: the
infectious, no reproductive particles called elementary bodies (0.3 lm)
and the noninfectious, intracytoplasmic, reproductive forms known as
initial (or reticulate) bodies (1 lm).
These organisms are obligate intracellular parasites, rod shaped to
coccoid, that reproduce by binary transverse fission. The diameter of the
individual cell is from 0.3–1 lm.
Mycoplasmas: Mycoplasmas are bacteria without rigid cell walls. They
are found in a wide variety of forms, the most common being the coccoid
(0.3–0.8 lm). Threadlike forms also occur in various lengths.
Fungi (Mycophyta) are nonmotile eukaryotes with rigid cell walls and a
classic cell nucleus. They contain no photosynthetic pigments and are
carbon heterotrophic, that is, they utilize various organic nutrient
substrates (in contrast to carbon autotrophic plants). Of more than 50 000
fungal species, only about 300 are known to be human pathogens. Most
fungal infections occur as a result of weakened host immune defenses.
Protozoa: Protozoa are microorganisms in various sizes and forms that
may be free-living or parasitic. They possess a nucleus containing
chromosomes and organelles such as mitochondria (lacking in some
Parasitic worms belong to the animal kingdom. These are metazoan
organisms with highly differentiated structures. Medically significant
groups include the trematodes (flukes or flatworms), cestodes
(tapeworms), and nematodes (roundworms).
These animals are characterized by an external chitin skeleton, segmented
body, jointed legs, special mouthparts, and other specific features.
This domain includes forms that live under extreme environmental
conditions, including thermophilic, hyperthermophilic, halophilic, and
methanogenic microorganisms. The earlier term for the archaea was
archaebacteria (ancient bacteria), and they are indeed a kind of living
fossil. Thermophilic archaea thrive mainly in warm, moist biotopes such
as the hot springs at the top of geothermal vents. The hyperthermophilic
archaea, a more recent discovery, live near deep-sea volcanic plumes at
temperatures exceeding 100 8 C.
This domain includes all life forms with cells possessing a genuine
nucleus. The plant and animal kingdoms (animals and plantlets) are all
eukaryotic life forms. Pathogenic eukaryotic microorganisms include
fungal and protozoan species.
Size of Microbes:
Microbes vary in size ranging from 10 nm (nanometers) to 100 mu
(micrometers) to the macroscopic.
Viruses in nm = 10-9 m (meter)
Bacteria in um = 10-6 m
Helminthes in mm = 10-3 m