1. General Bacteriology .pdf
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BY/ AHMED ABDEL-FTAH
Introduction to Medical Microbiology
Definition: micro (small) bios (life).
Microbiology is the science of study of living microorganisms or microbes which
are 1- simple in structure, 2- usually small in size and 3- cannot be seen with the
naked eye. They include bacteria, fungi, protozoa and viruses.
Importance: 1- Microorganisms are the cause of many diseases.
2- Other microorganisms used in manufacture of antibiotics and foodstuffs.
Creatures are classified into 5 kingdoms:
1- Animalia e.g. Helminths.
5- Monera: a- Cellular e.g. Bacteria.
3- Protista e.g. Protozoa.
b- Acellular e.g. Viruses
NB: 1. They all are Eukryotic except Monera which is Prokaryotic.
2. Bacteria and Viruses are prokaryotes & Protozoa and Fungi are eukaryotes.
3. Prokaryotes = Premature or not true nucleus & Eukaryotes = True nucleus.
Differences between eukaryotes and prokaryotes: (RCN 3M)
a. Chromosomal number
One copy (Haploid)
Two copies (Diploid)
b. Nuclear membrane
3. Cell wall
a. Cell wall Peptidoglycan
b. Cell wall sterols
5. Membrane bound organelles
Differences between medical important microorganisms (ROM3aNTICS)
1. Size (diameter)
3-10 μm (yeast)
2. Type of nucleus
3. Outer surface
4. Nucleic acid
RNA or DNA
Budding or Mitosis
Intra and Extra cellular
Shape of the
One curve e.g.
More than one
free living in
soil, air and
A. Gram positive
violet in color.
B. Gram negative
red in color.
C. Not stained by
Gram stain; but
1- Cell wall.
3- Capsule or slime
Surface structure (Bacterial envelope)
Definition: It is the rigid layer that lies outside the cytoplasmic membrane.
Chemical structure: The bacterial cell wall is composed of a substance referred to as
murein, mucopeptide, or peptidoglycan. There are special components present in
Gram positive and others in Gram negative.
Peptidoglycan: Thin (One or two sheets).
Comprising only 5-10% of cell wall.
Peptidoglycan: Thick (Up
to 40 sheets).
Comprising up to 50% of
Outer membrane: Thick & composed of:
-Lipid A (the endotoxin),
-Polysaccharide (somatic antigen).
membrane and outer membrane and contains
hydrolytic enzymes and penicillinase.
1- Teichoic acid: Either
ribitol or glycerol.
Functions (Importance): (3P-CAT)
1) Preservation of the shape of the cell.
2) Protection against high internal osmotic pressure.
3) Permeability of the cell: The cell wall is non-selectively permeable in general.
4) Antigenic character: Teichoic acid (in Gram positive) is major surface antigen &
Polysaccharide (in Gram negative) is major surface Ag called "O" antigen.
5) Toxicity: lipid A of Gram negative cell wall is responsible for endotoxin activity of
Gram negative bacteria.
6) Cell wall is responsible for Gram staining reaction.
7) Cell wall is target for antibiotics as penicillin, cephalosporin and vancomycin.
Cell wall deficient forms:
1) Protoplasts and
bacterial cell wall in
Protoplasts from Gram
Gram negative cells
(which retain outer •
They are spheroplasts or protoplasts
when are able to grow and divide.
• Some L-forms can revert to normal
by removing inducing agent.
• Some bacterial species produce Lforms spontaneously.
a) L-form infections are relatively
resistant to antibiotic.
b) May produce chronic infections
e.g. tonsillitis by Streptococcus
wall) so can
(2) Cell Membrane (Cytoplasmic membrane)
1. It is a very thin elastic membrane lie immediately under the cell wall.
2. It is a typical "unit membrane" composed of biphospholipids and proteins.
3. The membranes of prokaryotes differ from those of eukaryotic cells by the
absence of sterol. The only exception being Mycoplasma that incorporates
sterols (such as cholesterol).
1. Permeability and transport: It is the system of transport that enables the cell
to transport nutrients into and waste products out of the cell. The transport
mechanisms may be passive, active transport or group translocation.
2. Electron transport and oxidative phosphorylation: for energy production (ATP).
3. Excretion of hydrolytic enzymes.
4. Biosynthetic function: carries enzymes and molecules for biosynthesis of cell
wall, DNA and membrane lipids.
5. Chemotactic function: The receptors of binding and repellents present in
Definition: They are inward invagination of the cytoplasmic membranes inside the
cytoplasm increasing the surface area.
Structure and function: not know but may be:
a. The site of attachment of chromosome in cell division.
b. The excretion of extracellular enzymes as penicillinases.
(3) Capsule, Glycocalyx & Slime layer
Produced by some bacteria & consists of polysaccharides except in Bacillus anthracis
1. Glycocalyx: Extracellular gelatinous negatively charged polysaccharidecontaining material lie outside the cell (include capsule and slime layer).
2. Capsule: is condensed, well-defined layer closely surrounding the cell.
3. Slime layer: is used if the glycocalyx is loosely surrounding the cell.
Demonstration of capsule:
1. Gram stain: It appears as unstained halo around the organism.
2. India ink "Negative staining": which stains the background of the slide and
does not stain the organism. So, capsule appears as a clear area against black
3. Demonstration by Electron Microscope.
4. Serological demonstration: by Antigen/Antibody reaction (capsular swelling
reaction e.g. Pneumococci and H influezae).
1. It is a very important virulence factor as it protects bacterial cell from
2. Protect cell wall against bacteriophage, complement and lysozymes.
3. The capsular substance is usually antigenic (K-antigen), so can be used in
serodiagnosis or vaccine preparation as in N. meningitides.
(2) Pili "Fimbriae"
Definition Bacterial flagella are long thread-like, It is a short rigid surface
appendages formed by many
Gram negative bacteria.
1- Monotrichous: single polar flagellum 1- Ordinary pili.
2- Sex pili.
2- Lophotrichous: multiple polar flagellae
3- Amphitrichous: One flagellum in each
pole of the cell.
4- Peritrichous: flagella distributed over
the entire cell e.g. E. coli.
Structure 1. Long thread-like helical filaments 1. shorter and finer than
made up of contractile
flagella & Can be seen by
2. Occur in motile only.
2. Occur in motile as well as
3. They are spiral.
3. more or less straight
Function 1- It is the organ of Motility: Motility is 1- Ordinary pili:
beneficial in the following:
adhesion to host cells.
a. Movement towards nutrients.
b. Movement toward optimal oxygen 2- Sex pili:
concentration in aerobic bacteria.
attachment of donor and
c. Choosing the locality suitable for
d. Assist pathogenic bacteria in
penetration through a viscid 3- Pili of different bacteria
2- They are highly antigenic (H-antigens
Prokaryotes have no
true nuclei instead
they have a structure
known as nucleoid.
1- There is no nuclear
2- Nucleoid of most
molecules of a
complex molecular machine 2found within all living cells 3that serves as primary site of
protein synthesis (translation).
1- Bacterial ribosome is 70s
and consists of: Small
subunit 30s & Large
2- Composed of ribosomal
RNA (rRNA) molecules
and a variety of proteins.
observed in cytoplasm in
many bacterial species.
1- They are not permanent
or essential structures.
2- They store material may
be protein, lipid and
granules) in C.diphtheria.
(6) Bacterial Endospores:
Definition: Under certain unfavorable conditions, some bacteria are capable of
forming resistant endospores in vitro (outside the body).
Examples: Clostridium and Bacillus are examples of spore forming organisms.
1- It is not a means of reproduction, as one cell produces one spore that
germinates into one cell.
2- The spore is a resting cell, highly resistant to desiccation, heat and chemicals.
3- Spores may be oval, rounded, bulging or non-bulging.
4- It may be central, terminal or sub-terminal.
Sporulation: Begins when nutritional conditions become unfavorable.
1. DNA is replicated.
2. The nuclear material in the cell moves to one pole.
3. Cytoplasmic membrane invaginates to form the forespore.
4. Cytoplasmic membrane grow and engulf forespore within second membrane.
5. Cortex formation by deposition of Dipicolinic acid and calcium.
6. Formation of spore coat.
7. Release of endospores.
8. Rest of bacterial cells undergoes autolysis.
Germination: Once formed, spore has no metabolic activity & can remain dormant
for many years. Upon exposure to water and appropriate nutrients specific enzymes:
1. Degrade the coat.
2. Water and nutrients enter.
3. Germination into a metabolizing and reproducing bacterial cell occurs.
NB: Bacterial Ag
1- O-Ag : in cell wall.
3- H-Ag : in flagellae.
2- K-Ag : in capsule.
Bacteria multiply by: simple binary fission which includes
a. Growth in size (elongation) of the bacterium.
b. Division of the nuclear bodies.
c. Constriction originating from cell wall inwards.
d. Then the bacterium divides into two daughter cells.
Growth on solid media: produce colonies specific for each bacterial species.
Growth on fluid media: may give
a. uniform turbidity (facultative anaerobic bacteria)
b. surface pellicle (aerobic bacteria) or
c. Sediment leaving relatively clear medium (anaerobic bacteria).
III. Growth Requirements of Bacteria
(1) Bacterial Nutrition
(2) Gaseous Requirements
As regards nutrition, bacteria can be
sources (as CO2) as only source of
its carbon skeleton. These are
2. Heterotrophic bacteria: That require
organic sources of carbon. These
are pathogenic bacteria.
Nutrients needed by bacteria:
1. Basic elements: Needed in larger
amounts for structure as basic
b) Minor elements: Phosphorous,
2. Essential metabolites and growth
factors: needed in very minute
amounts for structure or as a
1. Oxygen: As regard O2 bacteria can
be classified into:
a) Obligatory aerobes: can grow only in
presence of free O2 (Mycobacterium
b) Facultative anaerobes: can grow well
in presence or absence of O2. They
possess two systems of aerobic and
anaerobic respiration. Most of
pathogenic bacteria belong to it.
c) Obligatory anaerobes: Grow in
absence of O2 and can't grow in
presence of oxygen due to lack of
peroxidase enzyme or catalase
enzyme so in presence of O2
peroxides will be formed which is
very toxic to organism.
d) Microaerophilic: grow best in
presence of a minimal amount of
oxygen as Campylobacter and
2. Carbon dioxide: is essential element
for growth of most of bacteria.
The normal atmospheric CO2 content is
usually sufficient, but some organisms
require higher concentrations of CO2
(5-10%) and this must be provided in
the culture media. These organisms
a) Stimulation of growth (capnophilic):
e.g. Neisseria & Brucella.
Temperature range: range between
minimum and maximum temperature
is between 10-42°C for most of
pathologic bacteria. Growth below
minimum temperature is called
psychophilic and above is called
(4) pH (Hydrogen ion
• For any
organism there is an
of pH. Optimum
of the organism
Some tolerate acidic media called
acidophilic as Lactobacillus.
A good amount of body of bacteria is
made of water and so, a high content of
water is essential for bacterial
cultivation. Mycobacterium tuberculosis
needs high concentration of moisture.
IV. Bacterial products
1) Bacterial enzymes: Enzymes need optimum temperature and pH for its action.
a) The enzymes may act on: 1-Protein called proteolytic enzymes.
2CHO called saccharolytic. 3-Lipids called lipolytic.
b) In addition, bacteria have respiratory enzymes as dehydrogenases and
2) Bacterial Pigments:
a) Endopiement: Which remain bound to body of organism and do not diffuse
into the surrounding medium. They are demonstrated on a solid media.
• Red pigment in Serratia marcescens
• Golden yellow in Staphylococcus aureus.
b) Exopigment: Which diffuse into the surrounding medium.
• Pseudomonas aeruginosa produces: Blue pigment called pyocyanin &
Yellow pigment called fluorescens.
▪ The pigments may play a role in bacterial respiration and also have
3) Bacterial toxins:
a) Exotoxins: These are diffusible toxins, which diffuse into surrounding medium.
b) Endotoxins: Remain bound to body of organism and released only when
▪ It can be prepared by growing of organism in fluid media. The culture then
filtrated through a bacterial filter. The filtrate constitutes the crude toxin.
Differences between Exotoxin and Endotoxin: (NS EL-ETiHAD)
Some Gram positive and
Cell wall of most of Gram
Protein in nature
Diffusible outside bacterial
High (1 μg is fatal)
Low (hundreds of μgs)
6. Heating at 60-80 °C
7. Effect of formalin
Detoxification giving toxoid
(used in vaccination)
8. Location of genes
Plasmid or bacteriophage
4) Other products:
1. Haemolysin: Produced by many bacteria as Staphylococcus aureus.
2. Leucocidins: Produced by Staphylococci and Streptococci and kill leucocytes.
3. Hyaluronidase: Dissolving hyaluronic acid (Cement substances between cells).
4. Coagulase: Produced by Staphylococcus aureus and causes clotting of plasma.
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