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					                    Basic Principle of Microbiology

-Different Between Eukaryotes & Prokaryotes :-

1-Eukaryotes ] Nucleus [ :-
This Cells Form (( Animals – Plants – Fungi –Algea )) .
- most eukaryotic cells would lyse at temperature extremes (both hot and cold), with
dryness, and with very dilute and diverse energy sources.

2- Prokaryotes ] No Nucleus [ :- This Cells Form (( Bacteria – Blue green Algea ))
- Use smaller Ribosome ( 70S ribosome ) .
- Bacteria can survive and, grow in hostile environments in which the osmotic
pressure outside the cell is so low.
- Bacteria have evolved their structures and functions to adapt to these conditions.
-Differences Among Prokaryotes :-
Bacteria can be distinguished from one another by their morphology (size, shape, and
staining characteristics) and metabolic, antigenic, and genetic characteristics.
Although bacteria are difficult to differentiate by size, they do have different shapes.
A spherical bacterium, such as Staphylococcus, is a coccus; a rod-shaped bacterium,
such as Escherichia coli, is a bacillus; and the snakelike treponeme is a spirillum. In
addition, Nocardia and Actinomyces species have branched filamentous appearances
similar to those of fungi. Some bacteria form aggregates such as the grapelike clusters
of Staphylococcus aureus or the diplococcus (two cells together) observed in
Streptococcus or Neisseria species.

- Bacterial Morphology Shapes :-

- Gram Stain :-

is a powerful, easy test that allows clinicians to distinguish between the two major
classes of bacteria. Bacteria that are heat fixed or otherwise dried onto a slide are
stained with crystal violet a stain that is precipitated with iodine, and then the
removed by washing with the acetone-based decolorizer and water. A red
counterstain, safranin, is added. This process takes less than 10 minutes.
-Gram Stain Procedures :-

-Result Of Gram Stain :-

1- Gram-positive bacteria :, Color is purple, Because They Have Thick
Peptidoglycan layers .
2- Gram-negative bacteria:- Color is Red, Because They Have Thin Peptidoglycan
layers .

- There are Bacteria cannot be classified by Gram stain Like mycobacteria, which
are distinguished with the acid-fast stain, and mycoplasmas, which have no

         Gram Positive Bacteria                      Gram-negative bacteria

Cell Wall :- Thick Peptidoglycan             Cell Wall :- Thin Peptidoglycan Layers
Layers + Tichoic acid + Lipotichoic          + Lipopolysacchraide ( LPS ) +
acid .                                       Phospholipid + Protein

- Function Of Cell Wall :-
1- Protect the internal parts of the cell
2- Give The shape of bacteria .
3- Prevent bacteria cell from lysis .

-Spores :- Found in some gram ve+ bacteria (( e.g bacillus anthracis , clostridium ))
are spore forming , but never gram ve- bacteria .
- spore be within a cell , and is a characteristic of the bacteria and can help in
identification of the bacterium.
- bacterial spores are so resistant to environmental factors .
- External structures of bacteria :-
1- Capsules :- Loose polysaccharide or protein layers surround the bacteria .
- it is major virulence factor .
- vi , k antigen found in capsule .

2- Flagella :- Provides motility for bacteria (( Motor Protein )) .
- it is allow cell to swim ((chemotaxis ))
- chemotaxis is :- toward food and away from poisons .
- H antigen is found in flagella .

3- Fimbriae (( Pili )) :- it is promote adherence (( Attachment )) to other bacteria or
the host .
- pili smaller than flagella in diameter .
- adherence factor (( Adhesin )) is pili important virulence factor for E.coli .
- O antigen is found in Pili .

- Biochemical Metabolism and Growth :-
obligate anaerobes :- bacteria cannot grow in the presence of oxygen.
obligate aerobes :- bacteria require the presence of oxygen for growth .
facultative anaerobes.:- bacteria grow in either the presence or the absence of
oxygen. .
autotrophs (lithotrophs) :- can rely entirely on inorganic chemicals for their energy
and source of carbon (CO2) .
heterotrophs (organotrophs):- bacteria and animal cells that require organic carbon
sources .

- Population dynamics :-

Lag phase :- adapt with environment in media without growing
Log phase :- the bacteria will grow and divide with doubling time ( multiply ) .
Stationary phase :- stop growing .
Decline :- death increased and stop growing.
Summary of various types of microscopes :-

1- Brightfield (( light )) microscope :- the basic components of this microscope
consist of :-
 a- light source (( to illuminate the specimens on the stage )) .
 b- condenser (( used to focus the light )) .
 c- two lenses to magnify image (( objectives + ocular )) .
- there are 3 different objective lenses are commonly used .:-
1- low power(( 10 fold magnification )), used to scan specimens .
2- high dry (( 40 fold )), used to look large microbes(( parasites – fungi ))
3- oil immersion (( 100 fold )) . used to observed(( bacteria + yeast )) and
morphologic details of larger organisms.
- the best brightfield microscope have resolving power approximately 0.2um .

2- darkfield microscope :- the same lenses used in brightfield microscope are used in
darkfield microscope .however special condenser is used in this microscope.
- resolving power is 0.02um . this allow to see extremely thin bacteria such as
 (( Treponema pallidum : etiologic agent of syphilis ))

3- phase – constrast microscope :- this microscope enables the internal details of
microbe to be examined .
The annular rings use in condenser and the objective lenses .
This microscope give three –dimensional image ((3D)) .

4- Fluorescence Microscope :- this microscope use fluorescent dyes ((stain)).
The microscope use high pressure mercury halogen or xenon vapor .

5- Electron Microscope :- unlike other forms of microscope , magnetic coils ((rather
than lenses )) this microscope used beam of electron instead((‫ )) بدال من‬of light .
Samples are usually stained by metal ions to create contrast .
There are two types of electron microscope:
    a- transmission electron microscope : in which electrons pass directly through the
        specimen , magnification of it is ((10000 – 100000 X)) and image in this type
        not give ((3D)) picture
    b- scanning electron microscope : magnify ((1000-10000X)) , the image I ((3D))