College of Medicine
Microbiology (Bacteriology)
Dr.Bara Hamid Hadi
----------------------------------------------------------------------------------------Introduction
Medical microbiology: the field of microbiology that deal with study of
pathogenic microorganisms and their interactions with human as causative agents of
infectious diseases. It covers the branches of bacteriology, virology, mycology,
parasitology and immunology. While the microorganisms/microbes are microscopic
living organisms which are very diverse and invisible by naked eye. They can be
found in nearly every environment. The life in our planet is impossible without
microbes due to their important role in generation of energy.
Types of microbial pathogens :
The pathogenic organisms of infectious diseases can be classified into five major
groups of organisms : viruses, bacteria , fungi , parasites and prion.
 Viruses: are the smallest infectious agents (20 nm-300 nm). They are smallest
10,000 time than bacteria.Viruses are intact particles and a cellular entities.
They contain one type of nucleic acid, either DNA or RNA surrounded by
protein coat. They are replicate only within living cells
 Bacteria : are single cells, larger and more complex than viruses. They have
cell wall and possess both types of nucleic acid (DNA,RNA), but lack true
nucleus and organelles( prokaryotic cell).They are replicate by binary fission.
 Fungi: are larger than bacteria and have more advanced cell structures. Fungi
have true nucleus (eukaryotic cell), cell wall and cellular organelles. They are
involved two types of organisms; yeasts (unicellular) and molds
(multicellular). They are replicate by budding or mitosis.
 Parasites: they are include two types: protozoa: are general term used to
refer to part of parasites which is unicellular eukaryotic cells, while
helminthes (metazoan) are more complex , multicellular eukaryotic cells.
 Prions: infectious particles that are composed of only protein. These proteins
have ability to cause disease. The prion diseases are called spongiform
encephalopathies include: Scrapie disease in sheep, Mad cow in cattle, Kuru
disease in human .
Not all microorganisms are harmful for human, but most microorganisms are benefit.
We swallow million microbes every day with not ill, but we are dependent on
microorganisms to help us digest our food .
Excellent example for benefit interaction between microbe and human is normal
microbial flora.
Normal microbial flora include various non-pathogenic bacteria and yeasts are
permanent residents of certain body sites, especially skin, mouth, nose, colon and
vagina , without cause any disease. All viruses and most parasites are not considered
to be member of normal microflora.

All types of cells can be divided into two different types according to nucleus type:
Prokaryote and Eukaryote . The differences between them are :
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1. The eukaryotic cell has a true nucleus with multiple chromosomes surrounded by
a nuclear membrane. The prokaryotic cell has not true nucleus but has single
circular loosely chromosome in cytoplasm lacking nuclear membrane.
2. All types of cells contain both types of nucleic acid(DNA and RNA) , except
viruses contain one type of nucleic acid ,either DNA or RNA.
3. The prokaryotic organisms are only unicellular, whereas eukaryotic organisms
either unicellular or multicellular.
4. Eukaryotic cells contain cellular organelles (such as mitochondria, lysosome,
large 80s ribosome, Golgi apparatus and others ), whereas prokaryotic cells
contain no organelles except small 70s ribosome .
5. Most prokaryotes have rigid cell wall that contain peptidoglycan, whereas
eukaryotes not contain peptidoglycan but have flexible cell membrane, except
fungi and plant cells have cell wall.
6. The prokaryotic cell (eg; bacteria) replicate by binary fission, whereas most
eukaryotic cells replicate by mitosis. During which one parent cell divided to
make two progeny cells. In contrast, viruses produce many copies of nucleic acid
and protein , then reassemble into multiple progeny viruses.
characters
Prokaryote
Eukaryote
Cell type
Unicellular
Multicellular
Nucleus
No
Yes
Chromosome One/plasmid
>1
Ribosome
Small 70s
Large 80s
Size
1-10 micron
10-100 micron
Example
Bacteria
Fungi, protozoan
 Classification of organisms:
All types of organisms (microorganisms and macroorganisms) classified into five
kingdoms:This classification scheme of organisms based on at least three major
criteria:
1. Type of cell : prokaryotic or eukaryotic.
2. Level of cellular organization: either unicellular or multicellular.
3. Type of nutrition: autotrophic or heterotrophic.
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There are five kingdoms of living things.
KINGDOM
Type of cell
Organism
Monera
Prokaryocyte
Bacteria
Actinomycetes
Protista
Eukaryocyte
Protozoa
Fungi
Eukaryocyte
Fungi
Plantae
Eukaryocyte
Plants, Moss
Animalia
Eukaryocyte
Arthropods
Mammals
Man
Scientific nomenclature:

Carolus Linnaeus (Sweden botanist, 1735) who have scientific nomenclature for all
forms of life(organisms).

Scientific nomenclature for organisms
(binomialnomenclature): genus and species.
is
consist
of
two
parts
Genus: a grouping of organisms that are closely related phylogenically.
Species: closely related strains that differ from all other strains.

Latinic form: First name in binomial system for genus and second name for species.
First letter of genus must be written in capital , whereas first letter of species must be
written in small form .

The Latinized name of genus and species for any organism must be written in Italic
form or place line under each genus and species.
Example: Staphylococcus aureus or Staphylococcus aureus
General properties of Bacteria:
1. The bacteria are prokaryotic cells which have not true nucleus but have
single circular loosely chromosome in cytoplasm lacking nuclear membrane.
2. The bacteria are unicellular, and contain no cellular organelles except small
70s ribosome .
3. Most bacteria have rigid cell wall that contain peptidoglycan , some may
have flexible or lack cell wall.
4. The bacteria replicate by binary fission. During which one parent cell
divided to make two progeny cells.
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Morphology of bacterial cells:

Shape : The bacteria are classified according to their shapes into four basic
groups:
Cocci: are spherical shape .
Bacilli : are rods shape
Spirochetes : are spiral–shaped.
Pleomorphic bacteria: they appear in many shapes.
 Size: the sizeof bacteria ranged from 1 to 10 micrometer(µm). In general,
cocci are about 1 micrometer in diameter, whereas bacilli are about 2-10
micrometer in length and 0.2-0.5 micrometer in width. N.B: Most cells of
microorganisms, animals, and plants are measured in micrometer (µm),
whereas viruses and cellular parts are measured in nanometer (nm).
 Arrangement of bacteria: Certain bacteria are arranged in single cell or in
pairs, some in chains, and others in groups.
First observation of cell by Hooke(1665). The first microscope is invented by Antony V.
Leeuwenhoek(1673), and he gives first description of microorganisms.
Louis Pasteur(1857) is father of microbiology. Robert Koch (1882) is father of clinical
microbiology especially in field of bacteriology.
L. Pasteur
R. Koch
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