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من قروب الصباحي مطرشينه ولهم كل الشكر
LFS 221/ Module 1
Basic Concepts of Medical Bacteriology
ý Introduction
Medical Bacteriology: The study of disease causing bacteria.
1) The ways by which they cause disease
2) The ways in which they are transmitted from man to man or animal to man
3) Methods of control & prevention, &
4) Laboratory diagnosis
The first three are of prime importance to all public Health Inspectors
However, prior to the detailed study of these organisms a general understanding of the concepts of medical bacteriology is required.
I. General characteristics of Bacteria
Living things may be divided into two categories, what are these categories??
Unicellular (single cells) or multicellular (Many cells) organisms.
Those organisms which are not seen by the naked eye (mostly unicellular) are referred to as …………? microorganisms “.
Bacteria are one type of microorganismsà Unicellular
Living organisms also divided into: ………………. &…………………...
Eukaryotes (those having a true nucleus with a nuclear membrane) & prokaryotes (those with no definite nucleus or nuclear membrane) Bacteria are ……….?
So, in short, bacteria are prokaryotic, unicellular microorganisms.
ý Classification
Plants & animals are mainly classified on the basis of their morphology ( their form & structure) Plants: E.g. the shape of the leaf,……Animals: E.g. whether the animal lays eggs or gives birth, or whether an animal has hair or feathers
Bacteria, in contrast to animals & plants, being unicellular, have a limited number of external structures to aid in their classification.
Some of the characteristics which are important in the classification of bacteria are:
*The shape of single cells, the shape of Clumps (groups of bacteria), Gram reaction, Ability to form spores, Biochemical reactions, Methods of motility
1. Shape OF Single Cells
Bacteria have a variety of shapes, & are of various sizes. The basic shapes include:
ü Cocci - round cells, Bacilli ( or rods ) - cylindrical in shape, Vibrio - Curved rods ( comma shaped ) ,Spirillum - spiral shaped ( like a spring ), Lancet shaped cocci - round with pointed ends, Coccobacilli - fat rods, Filamentous
2. Shape OF Clumps
Bacteria divide by Binary fission
Following division, the two cells may not completely separate. This results in many cells being attached to each other. Depending on the planes of division, these clumps may show a variety of shapes.
a. Division in one plane results in a string of bacteria ( strepto-). If these were bacilli, they would be referred to as streptobacilli, Division in two planes results in cells found in groups of 4 usually, Division in three planes results in cubes containing mostly 8 single cells, Division in two or three planes with no organization results in sheets or clumps with no particular shape.
3. Gram Reaction
Simple stains are used to enhance the visibility of these m.o.
A simple stain consists of staining with any type of stain which makes the bacteria look colored.
Depending on the color of the stain the bacteria could be red, green, purple etc.
ü Gram Stain
It allows us to separate bacteria into two main types ?? Gram- positive & Gram- negative
The method was developed by a Danish scientist by the name of Christian Gram in 1884.
The staining procedure consists of :
ü Preparation of a smear on a glass slide, Staining with crystal violet ,Addition of Gram’s iodine, Wash with Acetone or alcohol, Counter stain with saffranin stain
After step (c) all bacteria are stained dark purple or black. Step (d) consists of washing the stained smear with acetone. This is the most important step in the staining procedure. Some bacteria (depending on their type of cell wall) allow the acetone to enter inside the cell & wash out the crystal violet, so then become colorless after step (d), While others will not allow theacetone towash the stain & will stay dark. Step (e) consists of staining with another stain, saffranin - a red stain So at the end of the procedure some bacteria are stained dark purple
( G+) & others are stained red or pink ( G- ).
4. Ability to Form Spores
Some bacteria are able to develop resting structures under conditions which may be unfavorable to the growth of the vegetative cell ( such as extreme dryness, heat, lack of nutrients .... etc.). These structures are developed within the bacterial cells & are called endospores ( endo refers to inside ) They are referred to more simply asà Spores
Depending on the size & location of the spore inside the cell àdifferentiation is possible
Examples are: Central spores, Terminal spores, Sub terminal
Spores are smaller than vegetative cell, if larger than vegetative cell result in the cell looking like a club ( the wooden stick that a policeman carries).Spores are highly resistant to heat, dryness, radiation & lack of nutrients.
5. BIOCHEMICAL REACTIONS
Biochemistry: is the study of the chemistry of living things.
Study of chemical reactions which are performed by living cells & which are usually results of presence of organic catalysts called enzymes. Not all bacteria have the same enzymes, so the presence or absence of certain enzymes is used in classifying these bacteria. Example, bacteria are able to breakdown sugars (glucose, sucrose, lactose etc.).
To do this they need a set of enzymes.
Two possible ways to breakdown these sugars.??
In one of these pathways oxygen is needed à Oxidation
& In the other, oxygen is not needed à Fermentation
To test if an unknown bacterium is oxidative or fermentative??
The bacteria are inoculated into a medium which contains a sugar & the tube is incubated in the absence of oxygen. If the bacterium is fermentative it will breakdown the sugar & organic acids will be produced. The medium becomes acidic (low pH) & this can be detected by the addition of an indicator which changes color at different pH. So from this simple test, we can tell an important property of this unknown bacterium this will aid in bacterial identification & classification. Many other biochemical tests can be performed on bacteria with the same ease.
6. METHODS OF MOTILITY
Several methods of motility are exhibited by bacteria.
a. Flagella: The most common mode of bacterial locomotion, Hairlike structures attached to the bacteria at a variety of locations.
Polar flagella : the flagella are located at one or both of the poles of the cell.
There are - 3 types of polar flagellation: Monotrichous, Lophotrichous, Amphitrichous
Peritrichous where the flagella are all around the cell.
b. Gliding: Some bacteria demonstrate a unique mode of locomotion, The ability to move by gliding over a surface, The way this is achieved is still not understood.
C. Axial filaments: the spirochetes, which are spiral - shaped bacteria, have a flexible cell wall. They also possess an axial filament which extends from one pole to the other. This filament contracts, thus pressing the spiral into a tight spring, then relaxes which causes the cell to move in a screw-type motion. Are all bacteria have the ability to move??Some bacteria have no means of locomotion, & are thus immotile.
من قروب الصباحي مطرشينه ولهم كل الشكر
LFS 221/ Module 1
Basic Concepts of Medical Bacteriology
ý Introduction
Medical Bacteriology: The study of disease causing bacteria.
1) The ways by which they cause disease
2) The ways in which they are transmitted from man to man or animal to man
3) Methods of control & prevention, &
4) Laboratory diagnosis
The first three are of prime importance to all public Health Inspectors
However, prior to the detailed study of these organisms a general understanding of the concepts of medical bacteriology is required.
I. General characteristics of Bacteria
Living things may be divided into two categories, what are these categories??
Unicellular (single cells) or multicellular (Many cells) organisms.
Those organisms which are not seen by the naked eye (mostly unicellular) are referred to as …………? microorganisms “.
Bacteria are one type of microorganismsà Unicellular
Living organisms also divided into: ………………. &…………………...
Eukaryotes (those having a true nucleus with a nuclear membrane) & prokaryotes (those with no definite nucleus or nuclear membrane) Bacteria are ……….?
So, in short, bacteria are prokaryotic, unicellular microorganisms.
ý Classification
Plants & animals are mainly classified on the basis of their morphology ( their form & structure) Plants: E.g. the shape of the leaf,……Animals: E.g. whether the animal lays eggs or gives birth, or whether an animal has hair or feathers
Bacteria, in contrast to animals & plants, being unicellular, have a limited number of external structures to aid in their classification.
Some of the characteristics which are important in the classification of bacteria are:
*The shape of single cells, the shape of Clumps (groups of bacteria), Gram reaction, Ability to form spores, Biochemical reactions, Methods of motility
1. Shape OF Single Cells
Bacteria have a variety of shapes, & are of various sizes. The basic shapes include:
ü Cocci - round cells, Bacilli ( or rods ) - cylindrical in shape, Vibrio - Curved rods ( comma shaped ) ,Spirillum - spiral shaped ( like a spring ), Lancet shaped cocci - round with pointed ends, Coccobacilli - fat rods, Filamentous
2. Shape OF Clumps
Bacteria divide by Binary fission
Following division, the two cells may not completely separate. This results in many cells being attached to each other. Depending on the planes of division, these clumps may show a variety of shapes.
a. Division in one plane results in a string of bacteria ( strepto-). If these were bacilli, they would be referred to as streptobacilli, Division in two planes results in cells found in groups of 4 usually, Division in three planes results in cubes containing mostly 8 single cells, Division in two or three planes with no organization results in sheets or clumps with no particular shape.
3. Gram Reaction
Simple stains are used to enhance the visibility of these m.o.
A simple stain consists of staining with any type of stain which makes the bacteria look colored.
Depending on the color of the stain the bacteria could be red, green, purple etc.
ü Gram Stain
It allows us to separate bacteria into two main types ?? Gram- positive & Gram- negative
The method was developed by a Danish scientist by the name of Christian Gram in 1884.
The staining procedure consists of :
ü Preparation of a smear on a glass slide, Staining with crystal violet ,Addition of Gram’s iodine, Wash with Acetone or alcohol, Counter stain with saffranin stain
After step (c) all bacteria are stained dark purple or black. Step (d) consists of washing the stained smear with acetone. This is the most important step in the staining procedure. Some bacteria (depending on their type of cell wall) allow the acetone to enter inside the cell & wash out the crystal violet, so then become colorless after step (d), While others will not allow theacetone towash the stain & will stay dark. Step (e) consists of staining with another stain, saffranin - a red stain So at the end of the procedure some bacteria are stained dark purple
( G+) & others are stained red or pink ( G- ).
4. Ability to Form Spores
Some bacteria are able to develop resting structures under conditions which may be unfavorable to the growth of the vegetative cell ( such as extreme dryness, heat, lack of nutrients .... etc.). These structures are developed within the bacterial cells & are called endospores ( endo refers to inside ) They are referred to more simply asà Spores
Depending on the size & location of the spore inside the cell àdifferentiation is possible
Examples are: Central spores, Terminal spores, Sub terminal
Spores are smaller than vegetative cell, if larger than vegetative cell result in the cell looking like a club ( the wooden stick that a policeman carries).Spores are highly resistant to heat, dryness, radiation & lack of nutrients.
5. BIOCHEMICAL REACTIONS
Biochemistry: is the study of the chemistry of living things.
Study of chemical reactions which are performed by living cells & which are usually results of presence of organic catalysts called enzymes. Not all bacteria have the same enzymes, so the presence or absence of certain enzymes is used in classifying these bacteria. Example, bacteria are able to breakdown sugars (glucose, sucrose, lactose etc.).
To do this they need a set of enzymes.
Two possible ways to breakdown these sugars.??
In one of these pathways oxygen is needed à Oxidation
& In the other, oxygen is not needed à Fermentation
To test if an unknown bacterium is oxidative or fermentative??
The bacteria are inoculated into a medium which contains a sugar & the tube is incubated in the absence of oxygen. If the bacterium is fermentative it will breakdown the sugar & organic acids will be produced. The medium becomes acidic (low pH) & this can be detected by the addition of an indicator which changes color at different pH. So from this simple test, we can tell an important property of this unknown bacterium this will aid in bacterial identification & classification. Many other biochemical tests can be performed on bacteria with the same ease.
6. METHODS OF MOTILITY
Several methods of motility are exhibited by bacteria.
a. Flagella: The most common mode of bacterial locomotion, Hairlike structures attached to the bacteria at a variety of locations.
Polar flagella : the flagella are located at one or both of the poles of the cell.
There are - 3 types of polar flagellation: Monotrichous, Lophotrichous, Amphitrichous
Peritrichous where the flagella are all around the cell.
b. Gliding: Some bacteria demonstrate a unique mode of locomotion, The ability to move by gliding over a surface, The way this is achieved is still not understood.
C. Axial filaments: the spirochetes, which are spiral - shaped bacteria, have a flexible cell wall. They also possess an axial filament which extends from one pole to the other. This filament contracts, thus pressing the spiral into a tight spring, then relaxes which causes the cell to move in a screw-type motion. Are all bacteria have the ability to move??Some bacteria have no means of locomotion, & are thus immotile.
