Download Cell wall

 Topics Covered
 Host–Pathogen Interactions.
 Bacterial taxonomy.
 Bacterial cells structures
Host–Pathogen Interactions:
The factors determining the genesis, clinical picture and outcome of an
infection include complex relationships between the host and invading
organisms that differ widely depending on the pathogen involved. Despite this
variability, a number of general principles apply to the interactions between the
invading pathogen with its aggression factors and the host with its defenses.
The determinants of bacterial pathogenicity and virulence can be outlined as
follows:
1.
2.
3.
4.
5.
6.
Adhesion to host cells (adhesins).
Breaching of host anatomical barriers (invasins) and colonization of
tissues (aggressins).
Strategies to overcome nonspecific defenses, especially antiphagocytic
mechanisms (impedins).
Strategies to overcome specific immunity, the most important of which is
production of IgA proteases (impedins), molecular mimicry, and
immunogen variability.
Damage to host tissues due to direct bacterial cytotoxicity, exotoxins,
and exoenzymes (aggressins).
Damage due to inflammatory reactions in the microorganism: activation
of complement and phagocytosis; induction of cytokine production
(modulins).
The above bacterial pathogenicity factors are confronted by the following
host defense mechanisms:
1.
2.
3.
Nonspecific defenses including mechanical, humoral, and cellular
systems.
Phagocytosis is the most important process in this context.
Specific immune responses based on antibodies and specific reactions of
T lymphocytes (see chapter on immunology).
The response of these defenses to infection thus involves the correlation of a
number of different mechanisms. Defective defenses make it easier for an
infection to take hold. Primary, innate defects are rare, whereas acquired,
secondary immune defects occur frequently, paving the way for infections by
microorganisms known as “facultative pathogens” (opportunists).
Distribution of bacteria:
Bacteria are wide distributed in nature. In earth, air and water. The natural
control of bacterial growth by sun light.
Bactria is classified according to their nutriention in to:
1.
2.
Saprophytic bacteria :
It is living on dead organic matter.
Parasitic bacteria:
It is living on living tissue or organic living matter.
Bactria is classified according to their pathogenicity in to:
1.
Commensal:
It is living on the living tissue but without useful and harmfull e. x.
E.coli.
2. Symbiotic :
It is living on the living tissue and give useful for host e. x. Lactobacilli.
3. Pathogenic :
It is living on the living tissue and cause disease. e. x. T.B.
Bacterial cytology:
It is science deal with the study of structural of bacterial cell.
Bacterial are regarded as a unicellular simple structure of microscopically size with a
prokaryotic cell structure (primitive nucleus, no nuclear membrane, cell wall is thick
and rigid).
Bacterial shape:
The shape of bacteria classified according to the morphology:
1. Higher bacteria like filament.
2. Lower bacteria like unicellular.
3. Coci (cocus) like spherical
4. Bacillus rod shape
5. Spiral------------syphilis.
Bacterial cells are between 0.3 and 5 lm in size. They have three basic forms: cocci,
straight rods, and curved or spiral rods.
The nucleoid:
Also there is nucleus called nuclear region because there is no nuclear membrane also
called nuclear body.
Consists of a very thin, long, circular DNA molecular double strand that is not
surrounded by a membrane. Among the non-essential genetic structures are the
plasmids. The “cellular nucleus” in prokaryotes consists of a tangle of double-strand
DNA not surrounded by a membrane and localized in the cytoplasm. In E. coli (and
probably in all bacteria), it takes the form of a single circular molecule of DNA. The
plasmids are nonessential genetic structures. These circular, twisted DNA molecules are
100–1000! Smaller than the nucleoid genome structure and reproduce autonomously.
The plasmids of human pathogen bacteria often bear important genes determining the
phenotype of their cells (resistance genes, virulence genes).
The cytoplasmic membrane:
It is typical of living cells, a membrane covering the cytoplasm, it is thin delicate and
semipermeable. It is basically a double layer of phospholipids with numerous proteins
integrated into its structure. It is harbors numerous proteins such as permeases, cell wall
synthesis enzymes, sensor proteins, secretion system proteins, and, in aerobic bacteria,
respiratory chain enzymes.
Chemical composition of cytoplasmic membrane:
The chemical composition is lipoprotein; it can be seen in the microscope.
Demonstration of cell membrane:
When we put the bacterial cell in hypotonic solution, this lead to diffusion in water of
cytoplasm and shrinkage of the cytoplasmic membrane called plasmolysis. ‫لو لم يكن غشاء‬
‫السايتوبالزم موجود فأن االنكماش يحصل في كل الخلية وهذه العملية تفيد في حصولنا على صورة واضحة لجدار‬
‫الخلية‬Cell wall. The lipid molecules is usually demonstrated in the cell, it present in
Mycotuberculosis.
Mesosome:
It is convoluted membrane produced by the invagination of the cell membrane into the
cytoplasm, the function:
1. Is to carry all the vital process of metabolism.
2. Excretory function to the waste product of bacterial cell. It cannot see by the ordinary
microscope.
Cell wall:
The cytoplasmic membrane is surrounded by the cell wall, the most important element
of which is the supporting murein skeleton. The cell wall of Gram-negative bacteria
features a porous outer membrane into the outer surface of which the
lipopolysaccharide responsible for the pathogenesis of Gram-negative infections is
integrated. The cell wall of Gram-positive bacteria does not possess such an outer
membrane. Its murein layer is thicker and contains teichoic acids and wall-associated
proteins that contribute to the pathogenic process in Gram-positive infections.
Cell wall chemical composition:
1. Basal structure:
It is mucopeptide or glucopeptide, mucopeptide is N. acetyl glucosamine and N.
acetyl muramine acid, the penciline for example break the bond between N.a.g. and
N.a.m. .
2. Special structure :
Some bacteria have lipoprotein and other have techoic.
a- Techoic acid in a Gram +Ve bacteria.
b- Lipopolysaccharide in a Gram – Ve bacteria.
Mucopeptide is the better place of the action of the substrate such as pencilline.
Function of cell wall:
1. It protects and supported the thin cell membrane against the high osmatic pressure of
the bacterial cytoplasm.
2. It maintenance the normal shape of the bacterial cell as coccal, bacilli.
3. Cell wall responsible for viability of the bacterial cells .the osmatic pressure in the
cell is about 20% sucrose solution. If the bacteria present in the hypotic solution such
as 10% sucrose this lead to swelling and rapture this process called osmotic lysis.
Lysozyme solution makes digestion to the cell wall, this is very important in lab
experimental and when the cell wall digested the bacterial cell become irregular in
shape.
4. In the division of the bacterial cell wall invaginated and then complete separation.
5. Maintaining the cell's characteristic shape- the rigid wall compensates for the
flexibility of the phospholipid membrane and keeps the cell from assuming a
spherical shape
6. Countering the effects of osmotic pressure
7. Providing attachment sites for bacteriophages
8. Providing a rigid platform for surface appendages- flagella, fimbriae, and pili all
emanate from the wall and extend beyond it
9. Play an essential role in cell division
10.Be the sites of major antigenic determinants of the cell surface。
11.Resistance of Antibiotics
The cytoplasm:
The cytoplasm is watery sap contains a large number of solute low- and high-molecular
weights substances, RNA and approximately 20 000 ribosomes per cell. Bacteria have
70S ribosomes comprising 30S and 50S subunits. Bacterial ribosomes function as the
organelles for protein synthesis. The cytoplasm is also frequently used to store reserve
substances (glycogen depots, polymerized metaphosphates, lipids).it is surrounded by
thin membrane called cytoplasmic membrane .There is convoluted membrane called
Mesosome.
Capsules:
Many bacteria have capsules made of polysaccharides that protect them from
phagocytosis. Some bacteria have property to form capsule which surround completely
the cell wall. If the capsule is large and can be seen by ordinary microscope called
capsule if it can be seen in electronic microscop only, it called microcapsule.
Capsulate microbe ‫الحمى الفحمية‬
Nature
Anthrax bacilli
Polypeptide (protein)
Pneumococcus ‫جرثومة ذات الرئة‬
Poly saccharide
Streptococcus ‫ جرثومة التهاب اللوزتين‬Hyaluronic acid
Klebsiella
‫ جرثومة االلتهاب الرئوي‬Poly saccharide
These are all bacteria which have clear capsule .The first three is gram +positive, while
the last is gram – negative.
Development of capsule in bacteria:
The bacteria make or will develop its capsule under unfavorable condition.
Demonstration of capsule:
1. Ordinary stain----- appear a halo organ in the.
2. Negative India ink------- in this method we stain only the capsule and left the other
body of bacteria.
3. Polychrome M.B. ------- in the anthrax the capsule take pink while in the take blue
color.
Importance of capsule:
Assist of identification of the bacteria for ex. the author anthrax and the anthrax bacilli
are the same but the second has second capsule and dangerous while the first has no
capsule and no harmful.
Function of the capsule:
The proper function is a served but it though protects the organism against the
engulfing by WBC in process called phagocytosis.
Loose slimeomes:
It is mucoid extracellular excretion by cell capsule.
Locomotive organelles:
Motile bacteria possess flagella.
Bacterial Flagellum:
A thin appendage arising from one or more locations on the surface of
the cell wall
Cellular locomotion
Moves cell along gradients e.g. glucose
Types of Motility:
 Flagellated
 Flagellum coordinated movement
 tumbling movement
 Axial filament- spirochetes
 Gliding- no visible organelles
Flagella and motility:
It is not essential for bacteria but it present in motile bacteria ,it is flagitious
bacteria which is locomotion bacteria ,it is organism of cytoplasm ,it is thin ,delicate
,and very long ,the nature of flagella composed of protein called flagellin.
Classification of bacteria according to the flagella distribution:
1. Non-motile bacteria which called atrichus.
2. Single flagella which called monoitrichus.
3. Flagella on both poles which called Amphitricous.
4. Flagella or more in one or the two pole which called lophotrichous.
5. Flagella on the both pole and all body which called peritrichous.
Determination of flagella:
There are two methods to demonstration of flagella:
1- Electron microscope.
2- Ordinary microscop.
The bacteria must be
1. Present in fluid media.
2. Young bacteria cell 18-24 hour. The bacteria must be present in fluid media to help
them in its motion.
Types of motility:
1. Flagella motility
It is produce by flagella, it is active or sluggish )‫(خامل‬.
2. Protoplasmic motility
It is produce due to the contraction in the protoplasm.
3. Brownian(force motion)
Motion produce due to the impaction (‫ )تصادم‬of molecules surrounding the bacteria.
We must stain the bacteria by Gray stain and Mordant stain‫مثبت الصبغة‬
Adhesive organelles:
Attachment pili or fimbriae facilitate adhesion to host cells.
Biofilm:
Foreign body infections are caused by bacteria that form a biofilm on inert surfaces.
Spores:
Some bacteria produce spores, dormant forms that are highly resistant to chemical and
physical noxae.
Inclusion granules:
Inclusion granules which are storage granules.
Fimbria (Pilli):
An appendage of the bacterial cell , It is filamentous projection, it is originated from
the cell wall, the fimbria is shorter and firmer, it can see by electronmicroscop, there is
no relationship between motility and fimbria. To indicate that fimbria originated from
cell wall we put it in lysosome which digested the cell wall and the fimbria is absent.
Function:
It is assist the bacteria to adhesive to host cell .. It is used also for transfer of genetic
information and also pili also transfer plasmids.
Bacteria spores (Endospore):
Certain group of bacteria mainly Genus of Clostridium group and Genus of clostridium
group and Genus of B-Anthrax ,group have a property to form resting starvation ‫قلة الغذاء‬
and desiccation ‫ الجفاف‬.
Spore formers:
It is number of Clostridium and B-Anthrax .The spores is out side the bacteria opposite
to capsule which is present mainly inside the body cell.
Formation of spore:
Under the abnormal condition the accumulate in one side and surround by spore after
some time the present of spore occur and become free .under microscopic the spore is
appear retractile and impermeable to the stain .
Type of spore:
There are two basic types :
1. No bulging of cell (No distortion).
Spore cause no bulging to the cell, it is located either
a. Rounded central.
b. Oval central.
c. Oval sub terminal.
2. Spore causes bulging to the cell, It is located either
a. Oval central.
b. Oval central.
c. Round terminal.
These appear the importance of spore to the identification of bacteria.
Resistance and viability of spore:
Spore much more resistance to starvation, chemical, heat and desiccation than
vegetative bacteria .To kill the spore we need from 100-120 Co while the organism at
vegetative in 60 Co.
Resistance of spore due to:
1. Presence of impermeable spore wall.
2. Resistance of heat due low water contain in the spore(5-20%) this characteristic that
spore is more resistance to heat because in more water the coagulation is quickly and
the opposite is occur. The heating killing the bacteria by the coagulation of the water
present in the bacteria.
Protein (albumin) + 0
160 Co
Protein (albumin) + 50 % water
80- 90 C0.
Protein (albumin) + 70 % water
50- 60 C0.
So that the bacteria become more resistance to heat if there is less water. The little
amount of water in the spore due to the hydrostapic ‫ ماص للماء‬substance presents in it
what called calcium dipicalinat.
Germination of spores:
It means that the rapture is occur in spore wall and the emerged to the spores and then
become vegetative this get in favorable condition.
Demonstration of spore:
1. In the ordinary stain the spore appears unstained retractile vacuoles this used in case
of attached spore.
2. Modified Ziehl-Nelson stain
In this method used heat stain this will be penetrate the staining through spore wall
and the spore gets stain.