Microbiology:
Specialized area of biology that studies living
things ordinarily too small to be seen without magnification.
Microscopic Organisms are collectively referred to
as:
Microbes
Microorganism
Germs
Bugs
The major biological groups of microorganisms that
microbiologists study are:
Bacteria
Fungi
Protozoa
Algae
Virus
Importance of Microbe:
Microbes
generate more than half the oxygen we breathe, excavate huge underground
caverns, contribute mightily to the changes in our climate, and make up the
largest mass of living things on earth. Life originated with microbes and all
of life is derived from microbes. Life without higher organisms is possible,
but life without microbes is not. It’s no wonder that ours has been
called the planet of the microbes! Consequently, the future of biological
and planetary sciences lies in understanding the role microbes play in shaping
this earth and its inhabitants.” From a report of the American Academy
Microbiology should not be considered to be just another organismal biological science, but should be regarded as a foundation for all biologists, on the par with biochemistry, genetics, and the study of evolution. And much of this foundation is also needed for all students of all area of sciences.
Microbiology should not be considered to be just another organismal biological science, but should be regarded as a foundation for all biologists, on the par with biochemistry, genetics, and the study of evolution. And much of this foundation is also needed for all students of all area of sciences.
Branches of Microbiology:
The microbiology is so extensive and deals with
every aspect microbe-human and microbe-environment.
Applied Microbiology:
Immunology: Study of defense mechanism of body that
protects us against infection.
Epidemiology:
To monitor and control the spread of disease in communities.
Food Microbiology, dairy microbiology, and aquatic
microbiology:
Study the role of microbes, both beneficial and
detrimental, in consumable food and drink.
Agricultural Microbiology: Studies the relationships
between microbes and crops, with an emphasis on improving yield and combating
plant diseases.
Industrial Microbiology:
Study the use of microbes to produce or harvest
large quantities of useful and necessary materials such as vitamins, amino
acids, drugs and enzymes.
Genetic Engineering and Recombinant DNA Technology:
Study techniques that deliberately alter the genetic
makeup of organisms to induce new compounds, different genetic combination, and
even unique organism.
Characteristics of Microorganisms:
Eucaryotic cells
Procaryotic cell
Procaryotic cell:
All procaryotic are microorganisms and lack
a special cell body called nucleus.
Microorganisms are specified by:
Small Size
The concept of small size can be visualized by
comparing microbial groups with the larger organisms (figure).
Unicellular
Simplicity,
High growth rate
High Rate of Adaptability
Microscope
: Instrument for enlargement of small object.
Simple Microscope: Contains just a single
lens and a few working parts.
Compound Microscope: Composed of 2 magnifying
lens, visible light, a condenser (a special lens to converge or focus the rays
of light to a single point on the object). See figure.
A microscope should provide adequate magnification,
resolution and clarity of image.
Magnification:
Capacity of an optical system to enlarge small objects
.
Total magnification: Product
of the separate power of magnification of each lens.
Objective lens:
4-100 times
40 = high dry objective lens
100 = oil immersion objective lens
Ocular lens:
10 -20 times
Resolution: The
capacity of an optical system to distinguish or separate two adjacent objects
or points from each other.
Types of microscope:
summarized the differences between types of
microscopes.
Classification of Microorganism:
Two
basic cell lines have appeared during evolutionary history.
1.
Procaryotic cells--------Bacteria
2.
Eucaryotic cells--------Fungi, Algae, Protozoans, Heminth worm, animal
cells, and plant cells.
Procaryotic cells:
A.
Eubacteria(more common bacteria):
a.
Eubacteria (-) with cell wall
b.
Eubacteria (+) with cell wall
c.
Eubacteria with no cell wall ( mycoplasma)
B.
Archaebacteria:
Live
in extreme environments, (high temperature, high salt, or low PH ).
Bacterial
Structure:
Appendages:
They are not present on all species. Can be divided into two major subgroups:
A.
Those that provide motility.
flagella
and axial filaments
B.
Those that provide attachments.
fimbriae
and pilli
Flagella:
The
primary function of flagella is to confer motility or self-propulsion that is,
the capacity of a cell to swim freely through an aqueous habitat.
Structure of flagella:
Flagellum is composed of three distinct parts:
The
filament, the hook, and the basal body (figure).
Axial
filaments (fibers): A type of modified flagellum consist of a long, thin microfibril
inserted into a hook
Pilus and fimbria:
Pili
refer to the long appendages and fimbria refers to short appendages.
They
are involved in attachment of the bacteria to the host cells.
Pili
are found in gram negative bacteria and also involved in mating process
(conjugation).
ex:
fimbriae of streptococcus, and pili of E. coli.
Cell Envelope:
The
bacterial surface and wall are collectively called cell envelope.
Bacterial
surface:
The glycocalyx:
This
layer develops as a coating of macromolecules to protect the cell and in some
cases, help it adhere to its environment.
This
layer differ among bacteria
Slime
layer- protect bacteria from loss of water and nutrient (figure3.11 a).
Capsules
- This layer is bounded to the cell to some degree, and has a thick, gummy
consistency (Figure).
Cell wall:
This
structure determine the shape of bacteria and also provide the kind of strong
structural support necessary to keep bacterium from bursting or collapsing due
to changes in pressure.
Peptidoglycan:
The
relatively rigid, protective quality of the wall is due to the peptidoglycon.
This
compound is composed of a repeating framework of long glycon chains with peptide
fragments (figure 3.14 T).
The
amount of peptidoglycon varies among the general groups of bacteria.
Difference
in cell wall structure:
Hans
Christian Gram developed a staining technique that delineates two different
groups of bacteria (Gram positive and gram negative).
Gram positive cell wall-
The
cell wall of gram + bacteria is a thick sheet composed of numerous sheets of
peptidoglycon and tightly bound acidic polysaccharides (techoic acid and
lypotechoic acid).
Gram negative cell wall-
This
cell wall contain outer membrane,
a
thin sheet of peptidoglycan, and an
extensive
space between peptidoglycan
and
cell membrane( figure 3.16T).
The
outer membrane is similar to cell membrane in structure with lipids, polysaccharides, and Proteins.
Some
bacteria may lose their cell wall during part of their life (Figure 3.17 T).
Cell membrane:
A very thin flexible sheet completely
surrounding the cell's internal contents.
It is composed of phospholipids, and proteins. Its functions
relate to energy extraction, nutrient processing and synthesis.
It
is an important site of metabolic activities and synthesis of structural
macromolecules.
Protoplasm =Internal Content of Cell):
A
dense, gelatinous solution inside the bacterial envelope.
The protoplasm major components are:
1.
Cell pool:
It is composed of water, sugar, amino acid,
and salt.
2. Chromatin
body (bacterial chromosome):
Bacteria
do not have a nucleus and their DNA is not enclosed in nuclear membrane, but
DNA is aggregated in a dense area of the cell called nucleoid or Chromatin body
3. Plasmid:
Some
bacteria contain piece of circular DNA called plasmid which confer protective
traits upon bacteria (resisting drug and radiation).
4. Ribosomes:
Tiny
discrete units, special type of RNA which synthesize protein.
5. Mesosomes:
Cell
membrane folds up into cytoplasm and increases the internal surface area for
membrane function.
6. Granules:
Bacteria
may concentrate nutrients in granules of varying size, number and content.
These stored sources can gradually consume as required.
Week-2
Bacterial Endospore:
Endospore
or spore is a structure for withstanding hostile condition.
General
steps in endospore formation are shown in table 3.1 T
Features
of spores, including size, shape, and position in the vegetative cell are
useful in identifying some species of bacteria.
Bacterial Size, Shape and Arrangement:
Size-
a.
cocci- 0.5 to 3mM
b.bacilli-
0.2 to 2 mM in
diameter and 0.0.5 to 20 mM in length.
short
bacilli-0.2 to 2 mM
long
bacilli-0.5 to 50 mM
Shape-
a.
coccus- spherical or ball shape
b. Bacillus
or rod- Cylindrical
Short
rod called coccobacilli.
Long
rod called spirillum.
Arrangement:
1. Cocci-
single, paired, tetrad, cluster and chain (figure).
2. Bacillus-
single, paired, chain, and palisades (figure).
Bacterial
Endosperm (spore):
It
is a dormant structure for withstanding hostile condition.
General
steps in endospore formation
See
table 3.1 T
Features
of spores, including size, shape, and position in the
vegetative cell are useful in
identifying
some species of bacteria.
Spore
produced by gram + bacillus and clostridium
Bacterial
Size, Shape and Arrangement:
Size:
a.
Cocci- 0.5 to 3mM
b.
Bacilli- 0.2 to 2 mM in diameter and 0.0.5 to 20 mM in length.
Short
bacilli-0.2 to 2 mM
Long
bacilli-0.5 to 50 mM
Shape:
a.
Coccus-
Spherical
or ball shape
b. Bacillus
or rod-
Cylindrical
Short rod called coccobacilli.
Long rod called spirillum.
Arrangement
:
1. Cocci-
Single, paired, tetrad, cluster and
chain
(figure).
2. Bacillus-
Single, paired, chain and palisades (figure).
Reproduction:
Procaryotic
cell reproduce by binary fission
(Transverse
fission) or budding (Figure)
Bacterial
Growth:
a.
Growth in size of bacteria
B.
Growth in the number of bacteria or population growth.
Population
growth:
The
basis of population growth is cell division (reproduction) by binary fission.
Generation
time or doubling time:
Time
required for a complete fission cycle from parent cell to two daughter cells.
Generation:
A doubling process when the population
increases by a factor of 2.
Ex: start with 1 cell to 2 to 4 to
8 to 16
Generation 1
2 3
4
Pattern of bacterial growth (growth curve):
There
are four phases in growth curve
1-
Lag phase
2-
Exponential (log) growth phase
3-
The stationary phase
4-
Death phase (figure)
The
control of microbial growth is necessary in many practical situations, and
significant advances in agriculture, medicine, and food science have been made
through study of this area of microbiology.
Control of
growth: of microorganisms.
Two
basic ways:
(1)
by killing microorganisms
(2)
by inhibiting the growth of microorganisms.
Control
of growth usually involves the use of physical or chemical agents which
either
kill or prevent the growth of microorganisms.
Agents
which kill cells are called cidal agents;
agents
which inhibit the growth of cells (without killing them) are referred to as
static agents.
bacterial
cells.
Sterilization:
Defines as complete destruction or elimination
of all viable organisms in or on an object. There are no degrees of
sterilization: an object is either sterile or not.
Sterilization:
1. heat
2. radiation
3. chemicals
4. physical removal of cells.
Methods of Sterilization
Heat:
most important and widely used. For sterilization always consider type of heat,
time of
Application
of temperature to ensure destruction of all microorganisms, Endospores of
bacteria are considered the most thermoduric of all cells so their destruction
guarantees sterility.
Incineration:
burns organisms and physically destroys them, used for needles, inoculating
wires, glassware, etc.
Boiling:100o
for 30 minutes. Kills everything except some endospores (Actually, for the
purposes of purifying drinking water 100o for five minutes is probably adequate
though there have been some reports that Giardia cysts can survive this
process). To kill endospores, and therefore sterilize the solution, very long
or intermittent boiling is required.
Autoclaving
(steam under pressure or pressure cooker): 121o for 15 minutes (15 am pressure).
Good for sterilizing almost anything, but heat-labile substances will be
denatured or destroyed.
Dry
heat (hot air oven): 160o/2hours or 170o/1hour. Used for glassware, metal, and
objects that won't melt.
Table 1.
Recommended use of heat to control bacterial growth
Treatment
Temperature
Effectiveness
Incineration
>500o
Vaporizes
organic material on
nonflammable
surfaces but may destroy
many
substances in the process
Boiling
100o
30 minutes
of boiling kills microbial
pathogens and vegetative forms
of bacteria
but may not
kill bacterial endospores
Intermittent boiling
100o
Three 30-minute
intervals of boiling,
followed by
periods of cooling kills
bacterial
endospores
Autoclave and
Pressure
cooker
(steam under
pressure)
121o/15
minutes at 15#
pressure
kills all
forms of life including bacterial
endospores.
The substance being sterilized
must be
maintained at the effective T for
the full
time
Dry heat
(hot
air oven)
160o/2 hours
For
materials that must remain dry and
which are
not destroyed at T between
121o and 170o Good for glassware, metal,
not plastic
or rubber items
Dry heat
(hot
air oven)
170o/1 hour
Same as
above. Note increasing T by 10
degrees
shortens the sterilizing time by 50
percent
Pasteurization
(batch
method)
63o/30 minutes
kills
most vegetative bacterial cells including
pathogens
such as streptococci,
staphylococci
and Mycobacterium
tuberculosis
Pasteurization
(flash method)
72o/15 seconds
Effect on bacterial cells
similar to batch
method; for
milk, this method is more
conducive to industry and has fewer
undesirable effects on quality
or taste
Irradiation:
Usually
destroys or distorts nucleic acids. Ultraviolet light is usually used (commonly
used
to sterilize the surfaces of objects), although x-rays and microwaves are
possibly useful.
Filtration:
Involves
the physical removal (exclusion) of all cells in a liquid or gas, especially
important to sterilize solutions which would be denatured by heat (e.g.
antibiotics, injectable drugs,
amino
acids, vitamins, etc.)
Chemical
and gas:
(formaldehyde,
glutaraldehyde, ethylene oxide) toxic chemicals kill all forms of life in a
specialized gas chamber.
Control of Microbial Growth by Physical Agents
Applications
of Heat:
The
lethal temperature varies in microorganisms.The time required to kill
depends
on the number of organisms, species, nature of the product being heated, pH,
and
temperature.
Whenever heat is used to control microbial growth inevitably both time and
temperature
are considered.
Sterilization
(boiling, autoclaving, hot air oven) kills all microorganisms with heat;
commonly
employed
in canning, bottling, and other sterile packaging procedures.
Pasteurization:
Use
of mild heat to reduce the number of microorganisms in a product or food.
In
the case of pasteurization of milk the time and temperature depend on killing
potential pathogens that are transmitted in milk, i.e., staphylococci,
streptococci, Brucella abortus and Mycobacterium tuberculosis. For
pasteurzation of milk: batch nethod: 63o/30minutes; flash method: 71o/15
seconds.
Low
temperature (refrigeration and freezing): Most organisms grow very little or
not at all at 0o.
Store
perishable foods at low temperatures to slow down the rate of growth and
consequent spoilage of the food (e.g. milk).
Low temperatures are not bactericidal.
Psychrotrophs, rather than true psychrophiles, are the usual cause of food
spoilage in refrigerated foods.
Drying
(removal of H2O): Most microorganisms cannot grow at reduced water activity (Aw
<
0.90).
Often used to preserve foods (e.g. fruits, grains, etc.). Methods involve
removal of water
from
product by heat, evaporation, freeze-drying, addition of salt or sugar.
Irradiation
(microwave, UV, x-ray): Destroys microorganisms as described under
"sterilization".
Many
spoilage organisms are easily killed by irradiation. In some parts of Europe , fruits and vegetables are irradiated to increase
their shelf life up to 500 percent. The practice has not been
accepted
in the U.S.
Control of microbial growth by chemical agents
Antimicrobial
agents are chemicals that kill or inhibit the growth microorganisms.
Antimicrobialagents include chemical preservatives and antiseptics, as well as
drugs used in the treatment should not be taken internally. Examples:
mercurials, silver nitrate, iodine solution, alcohols, detergents.
Disinfectants:
Agents
that kill microorganisms, but not necessarily their spores, not safe for
application
to living tissues; they are used on inanimate objects such as tables, floors,
utensils, etc. Examples: chlorine, hypochlorites, chlorine compounds, lye,
copper sulfate, quaternary ammonium compounds.
Note:
disinfectants and antiseptics are distinguished on the basis of whether they
are safe for application to mucous membranes. Often, safety depends on the concentration
of the compound. For example, sodium hypochlorite (chlorine), as added to water
is safe for drinking, but "chlorox" (5% hypochlorite), an excellent
disinfectant, is hardly safe to drink. Common antiseptics and disinfectants and
their uses are summarized in Table 2.
Table 2. Common antiseptics and disinfectants
________________________________________________________________________________
Chemical Action Uses____________________________
Ethanol
(50-70%)
Denatures proteins and
solubilizes
lipids
Antiseptic used
on skin
Isopropanol
(50-70%)
Denatures proteins
and
solubilizes lipids
Antiseptic
used on skin
Formaldehyde
(8%)
Reacts with NH2,
SH and
COOH groups
Disinfectant,
kills endospores
Tincture of Iodine
(2%
I2 in 70%
alcohol)
Inactivates proteins
Antiseptic
used on skin
Chlorine
(Cl2)
gas
Forms hypochlorous acid
(HClO), a strong
oxidizing
agent
Disinfect
drinking water; general
disinfectant
Silver nitrate
(AgNO3)
Precipitates
proteins
General
antiseptic and used in the
eyes
of newborns
Mercuric chloride
Inactivates
proteins by
reacting with
sulfide
groups
Disinfectant,
although
occasionally used as an antiseptic
on
skin
Detergents
(e.g.
quaternary
ammonium
compounds)
Disrupts cell
membranes
Skin antiseptics and disinfectants
Phenolic compounds
(e.g.
carboloic
acid, lysol,
hexylresorcinol,
hexachlorophene)
Denature proteins
and
disrupt cell
membranes
Antiseptics at low
concentrations;
disinfectants at
high
concentrations
Ethylene oxide gas Disinfectant used to
sterilize
heat-sensitive
objects such as rubber and plastics
Examples;
calcium propionate, sodium benzoate, formaldehyde, nitrate, sulfur dioxide.
Table 3 is a list of common preservative and their uses.
Table 3. Common food
preservatives and their uses
Preservative Effective Concentration Uses
Propionic acid and
propionates
0.32%
Antifungal agent in breads, cake, Swiss
cheeses
Sorbic acid and
sorbates
0.2%
Antifungal agent in cheeses, jellies, syrups,
cakes
Benzoic acid and
benzoates
0.1%
Antifungal agent in margarine, cider,
relishes, soft drinks
Sodium diacetate
0.32%
Antifungal agent in breads
Lactic acid
unknown
Antimicrobial agent in
cheeses, buttermilk,
yogurt and pickled foods
Sulfur dioxide,
sulfites
200-300 ppm
Antimicrobial
agent in dried fruits, grapes,
molasses
Sodium nitrite
200
ppm
Antibacterial
agent in cured meats, fish
Sodium chloride
unknown
Prevents microbial spoilage of meats, fish,
etc.
Sugar
unknown
Prevents microbial spoilage of preserves,
jams,
syrups, jellies, etc.
Wood smoke
unknown
Prevents microbial spoilage of meats, fish, etc.
Methabolism
Cellular
chemical change resulting from all chemical reactions and physical working of
the cell
Two
general categories :
a.
Anabolism or biosynthesis-
Any
process that result in the synthesis of cell’s molecules or structures- forming
larger molecule from smaller molecules.
b.
Catabolism-
Breaking
down of large molecule and producing energy.
The
linking of anabolism to catabolism complete many thousands of cellular
processes (transport, growth, motility, ...)
Enzyme:
Enzymes
facilitate reaction by lowering energy of activation.
Majority
of cellular reaction are catalyzed by enzyme and each enzyme act specifically upon
its assigned metabolite called substrate.
Enzyme speed up the rate of metabolic activity.
Majority of
cellular reaction are catalyzed by enzyme. Enzymes are protein and act
specifically upon their assigned metabolites called substrates.
Enzyme speed up the rate of
metabolic activity
Type of Metabolism:
A.
Fermentation
Some
bacteria obtain metabolic energy by a Substrate Phosphorylation.
B.
Respiration
Some
bacteria obtain metabolic energy by an Oxidative Phosphorylation.
C.
Photosynthesis
Metabolic
energy obtained by Cyclic Phosphorylation (Similar to respiration except that
photochemical processes using energy of light).
Does
not occur in any medically important bacteria
Microbial Genetics:
Genetics (Genesis, birth, generation):
Study of the inheritance or heredity living
things(microorganisms and microorganisms).
Genetic Material:
Long, encoded molecule of DNA with several orders of
structure
Genome:
Total of genetic materials of a cell.
Size of genome varies from 4-5 genes (virus) to more
than 10000(human, and plants).
E. coli contains 3000 genes.
Chromosome: Cellular structure composed of a Long,
neatly packaged piece of DNA.
Gene:
1-Thefundamental unit of heredity responsible for a
given trait in an organism
2- Site on the chromosome that provides information
for a certain cell function.
3-A certain segment of DNA that contains the
necessary code to make a protein or RNA molecule.
DNA and its code:
1. DNA
Structure: Nucleic acid with two polynucleotide strands combined into a double helix. It consists of a deoxyribose sugar- phosphate
attached to nitrogenous base (figure).
2. DNA
Code: The order of bases along the
length of the DNA strand constitutes the genetic program-the language - of the
DNA code.
DNA Replication:
DNA replication requires the action of 30 enzymes.
The basic steps of replication of DNA are:
1- Uncoiling
2- Unzipping
3- Biosynthesis of complementary
polynucleotide (figure).
Semi-conservative Replication
Preserving the DNA code and passing it on the
daughter cells
Protein synthesis:
Transcription and Translation of DNA:
Transcription: Code of DNA is copied onto an RNA
molecule (a messenger), (figure).
Translation: RNA message is decoded by special cell
components into proteins (figure).
Gene Regulation in bacteria:
A inducible Operon
The operon is normally in an off mode and does not
initiate the enzyme synthesis when the substrate is not present. ex Lactose Operon(
Inducible)
The control through genetic induction is explained
by lactose (lac) operon. It is made up
of three segments or loci: Regulator,
Control Locus and Structural Locus.
1- Regulator:
Composed of a gene that code a protein capable of
repressing the operon ( a repressor).
2-Control Locus:
Composed of two genes, the promoter (identified as a
palindrome) and the operator ( where transcription of the structural gene
initiated).
3-Structural Locus:
Made up of three genes, each coding for a different
enzyme ( Beta galactosidase, permease, and transacetylase) needed to catabolize
lactose.
B. Repressible Operon:
This operon
is a bacterial system for amino acid, purine and pyrimidine synthesis. A
repressible operon governs anabolism.
This operon is normally in the one mode and will be turned off only when
this nutrient no longer required
Mutation: Change in Genetic code
1-Any permanent, inheritable change, in the genetic
information of cell is a mutation.
2- An alteration in the nitrogen base sequence of
DNA.
Wild type strain =Natural strain
Mutation = Mutant strain
Spontaneous mutation:
A random change in the DNA (mistake in DNA
replication)
Effect of natural background radiation (cosmic rays)
Induced mutation:
Exposure to mutagens(physical or chemical agents
that interact with DNA in a destructive manner)
Point Mutation:
Change in a few bases (addition, removal or
substitution).
Missense Mutation:
A change in the code that leads to placement of a
different amino acid
Nonsense Mutation:
This mutation changes a normal codon into a stop
codon that does not code for an amino acid and stop the production of protein.
Repair of mutations:
Cell has a system for finding and repairing DNA that
has been damaged by various mutagens.
Most
ordinary DNA damage is resolved by enzymatic systems specialized for such
defect (figure).
Effect of Mutations:
Negative Effect: Human gene
mutation alteration in a single protein is responsible for more than 400
diseases.
EX:
Sickle cell anemia( figure)
Positive Effect: Microbial mutation Certain microorganisms
bearing protective mutation can adapt to the new environment.
Genetic
Recombination (Genetic exchange):
It is a mechanism which
bacteria have developed for increasing their adaptive capacity. One bacterium donates DNA to another
bacterium (intermicrobial transfer) and the end product result is a new strain
different from both.
The genetic exchanges are
usually beneficial to bacteria. and provide additional genes for resistance
against drugs, metabolic poisons new
nutritional and …
Plasmids (extrachromosomal
DNA) are small genetic elements capable of independent replication in bacteria.
Plasmids are evolved in DNA
recombination.
Mechanism of Gene transfer:
There are three types of
exchange:
1-
Conjugation (Bacterial sex):
Require the attachment of
two related species through a pilus and the presence of a special plasmid
(Figure)
2-Transduction:
Bacterial transfer mediated
through the action of a bacterial virus ( figure)
3-Transformation
Transfer of naked DNA and
requires no special vehicle. A bacterial nonspecific acceptance of small
fragment of a soluble DNA from the surrounding environment, the process is
useful for DNA recombinant.
One sort of the genetic
transferal called transposons. Genes have the distinction of shifting from one
side to the other side termed jumping genes.
DNA
Technology and Genetic Engineering:
Specified DNA fragment can
be isolated, amplified, and their genes can be expressed at high levels.
1. Preparation of DNA
fragments:
Restriction Endonuclease
enzymes cut DNA at specific sites (Figure). Hundreds of restriction nucleases
are presently known and each having a particular sites as its target.
2. Separation of DNA
fragments
Gel electrophoresis permits DNA fragments to be
separated to be on the basis of size (Feature).
The dye ethidium bromide can
bind to DNA, forms a bright fluorescent adduct, and permit the visualization of
fragments of DNA in gel(Figure ).
3. Coloning of DNA
restriction fragments:
Many restriction enzymes
produce DNA fragments with sticky ends.This DNA can be used as a donor with
plasmid recipients to form genetically engineering plasmids.
Recombinant plasmids may be
introduced into a bacterial a bacterial host ( frequently E. Coli) by
transformation( Figure).
The
Influence of Environmental factors on Microbes
Environmental
factors:
1-
Temperature:
Minimum Temperature:
The lowest temperatures that
permit a microbe’s continued growth and metabolism; below this temperature its
activities and growth are genetically inhibited.
Maximum temperature:
It is the highest
temperature at which growth and metabolism can proceed. If the temperature
arises slightly above maximum, growth will stop, but if it continues to rise
beyond this point, the enzymes and nucleic acid will become permanently
inactivated and the cells will dye.
Optimum temperature:
It is a small range,
intermediate between the minimum and maximum, which promotes the fastest rate
of growth and metabolism.
Pschrophile: A microorganism
that grows optimally below 15°C and is capable of growing
at 0°C.
Mesophiles: Microorganisms
that grow at moderate temperature (20-40°C)
Human pathogen: 30-40°C.
Thermoduric: Microorganisms
that can survive short exposure to high temperature are normally mesophiles
(such as spore forming or thick walled microbes).
Thermophile: A microbe that
grows optimally at temperatures greater than 45°C.
Such heat -loving microbes
in soil and water associated with volcanic activity. General ranges of (45-80°C).
Most eucaryotic forms can
not survive above 60°C, but a few thermophilic
bacteria grow around 25°C.
Gas:
The three atmospheric gases
that most influence microbial growth are O2, CO2 and N2.
Effect of O2 on microbial growth.
1. Aerobic Microorganism: A
microorganism that grow well in the presence of normal atmospheric oxygen and
possesses the enzymes (catalase, and desmutase) needed to process toxic oxygen
product (Figure)
2. Facultative anaerobe: Microorganism capable
of growth in the absence and presence of oxygen. Oxygen is not absolutely
required for its metabolism. These microorganisms have catalase and dismutase
enzymes.
3. Microaerophyle: A
microorganism that does not grow at normal atmospheric tensions but requires a
small amount of oxygen in metabolism.
4. Anaerobe: Microorganism
that do not grow in normal atmospheric oxygen, and it lacks the metabolic
enzyme system for using oxygen.
Other factors such as pH, osmotic
pressure,
and radiation also influence microbial growth.
Microbial
Interactions:
Another influence on the
growth of microorganism comes from other organism that shares their habitats.
1. Interrelationships may
occur between microbes.
2. They may involve
multicellular organism such as plant or animals.
3. They can have beneficial,
neutral, or harmful effects on the organism involved.
Symbiosis: A simple cohabitation of organisms.
Synergism: A cooperative
relationship between organisms that is beneficial to both members but not
obligatory.
Commensalism: One member (A)
is neither harmed nor benefited, yet A provides benefits to the other member B.
Parasitism: A harmful
interrelationship.
Antagonism: A kind of parasitism when members of a
community compete. One microbe secretes antimicrobial chemical that inhibit or
destroy another microbe in the same habitat.
Antimicrobial Chemotherapy
Definition:
Chemotherapeutic
Drug
Antimicrobial
Chemotherapy
History:
19
century Paul Ehrlich- Arsenic based drug- Syphilis
1929
– Fleming Penicillin (discovered antibiotic by accident)
1935-
Domagk Sulfa Drug
1940-
Chain and Flory- Penicillin effective chemotherapeutic substande
1950-
Drug and Research Development
1950-
Modern Antimicrobial Drugs
Types
of Drugs:
Antibiotic:
Natural substance of Fungus (not made in a lab) produced by Fungi and kills bacteria.
Synthetic:
Non- natural substance
Semi-synthetic:
Natural substance that is altered in the lab
Bacterial
infection would use antibiotic or semi- synthetic drug
Viral
infection would use a synthetic drug.
Scope
of Activity:
Narrow
Spectrum Bacitracin:
Broad
Spectrum Tetracycline:
Drug
Administration:
Oral
Injection
(intravenous, and intramuscular, skin- body cavity)
Topical
(skin surface)
Interaction
of Drug- Cell Microorganism
1-
Absorption (cells or body fluid)
2-
Delivery (Carry to infected area)
3-
Drug Function (destroys the infectious agent or inhibits its growth)
4-
Breaking Down of Drug by the host Organ
Selective
Toxicity:
Selective
Toxicity function of:
a.
receptor for drug
attachment
b.
inhibition of
biochemical events essential for the parasite but not hose
c.
microbicidal
rather than microbiostatic
d.
soluble ( to
allow delivery)
e.
no resistance
f.
remain potent for
a long time
g.
do not cause
allergy
Mechanism
of action:
Mechanism
of Action of Antimicrobial Agents
(Drug
used for bacterial infection)
1-
Cell wall
synthesis
2-
Cell membrane
function
3-
Protein synthesis
4-
Nucleic acid
synthesis
Inhibition
of Cell Wall Synthesis
Animal
Cell
Bacterial
Cell
Shape
of Microorganism
Protect
Against Hypotonic Environment
Cell
Wall:
Rigid
Peptidoglycon
Gram
+ and Gram –
Protoplast-
Gram +
Spheroplast- ( Gram - )
b-
lactam ( Penicillin, and Cephalosporins)
drugs
Inhibitor
of cell wall synthesis
Interact
with one or more enzyme required for peptidoglycon synthesis
Development
of peotidoglycon deficient weak points
Bacteriocidal
Note
effective against old or dormant cell
Effective
against young cells
Inhibition
of Cell Membrane Function:
Damaged.
Membrane-
Metabolic
insufficiency
Lysis
and cell death
Polymyxin
(gram -)
Polyenes
( Fungi_
Imidazoles
(Fungi)
Microbiocidal-
Toxic to human
Inhibition
of Protein Synthesis:
Bacterial
ribosomes 70S
Mammalian
cell ribosome 80S
Not
toxic to human; toxic to bacteria. They prevent
Selective
against bacterial ribosome but not in mammalian ribosome
Two
possible target of ribosomal inhibition:
30S
subunit
50S subunit
Inhibition
of Nucleic Acid Synthesis:
Requirement
of specific enzyme for DNA or RNA replication
Blocking
the synthesis of the enzyme
Inhibition
of nucleic acid synthesis
Rifampin
Binds
to DNA depend RNA polymerase inhibit bacterial RNA synthesis
Sulfanamide
(sulfa drug)
The
synthetic drugs termed antimetabolites model of competitive inhibition
Very
similar to the natural metabolic compound PABA ( para-aminobenzoic acid) that
is needed by bacteria to synthesize Folic (nucleic acid)
Drug
Resistance
Wide
scale use of drug
Adaptation
of microorganism to tolerate usual dosage of the drug
High
number of
Origin
of Drug Resistance
Non-genetic
Genetic
a.
Chromosoisal
Resistance
Spontaneous mutation in a locus that controls
susceptibility to given antimicrobial drug
a.
change in the
structural receptor for a drug
ex: Rifampin, Sterptomycin, Erythromycin,
Lincomycin, and Aminoglycosides
b Extrachromosomal Resistance
Chemotherapeutic agents: antimicrobial
agents of synthetic origin useful in the treatment of microbial or viral
disease. Examples: sulfonilamides, isoniazid, ethambutol, AZT, chloramphenicol.
Note that the
microbiologist's definition of a chemotherapeutic agent requires that the agent
be used for antimicrobial purposes and so excludes synthetic agents used for
therapy against diseases that are not of microbial origin.
Plasmid
R Factor- Plasmids that carry genes for
resistance to one or several antimicrobial
Plasmid
genes for antimicrobial resistance often control the formation of enzymes
capable of destroying the antimicrobial drugs
The
genetic material of R factor can be transferred by :
Transduction
Transformation
conjugation
Specific
Mechanism of drug resistance
1- Synthesis of enzyme for inactivation of drugs
2- Decrease in cell permeability for uptake of drug
3- Change in the
number of affinity of the drug receptor sites
4- Modification of an essential metabolic pathway
Cross-
Resistance:
Microorganism
resistance to certain drug may also be resistant to other drugs that share a
mechanism of action
Limitation
of Drug Resistance
To
minimize the emergence of resistance
1-
maintain high
level of drug in the issue
2-
simultaneously
administer tow drugs which are not cross resistance
3-
avoid exposure of
microorganism to a particularly valuable drug by restricting it use
Antibacterial drugs
Penicillin- antibiotics- end in the end with suffix cillin
Penicillium notatum
Penicillium chrysogemun
Prevent formation of cell most effective against gram
+
B Lactam drug
Cephalosporins-
new antibiotics
Cephalosporium
acermonium
B
Lactam drug
Broad
spectrum (gram +, gram -, etc)
Tetracycline
Yellow
colony of steptomyces
Chemically
altered and called teracyclien
Semisynthetic
Broad
spectrum ( gram +, gram-)
Inhibition
of protein synthesis
Antiviral
Drug
Drug
development in infancy
Narrow
spectum- most drug acts inside the cell
Compounds
control replication by
1-
c Blocking complete adsorption and /or
penetration of the virus into the host cell
2-
Blocking the
transcription and translation of viral molecules
3-
3. preventing the
maturation of viral particles
The
mode of action of antivirals mimics the structure of the nucleotide and compete
for sites on replication DNA
Incorporation
of they synthetic nucleotides inhibits further DNA synthesis
Examples
Acyclovir
(Zovirax)
Purine-
Prevent
the action of viral thymidine kinase and block DNA synthesis- Herpes infection
AZT
azidothymidine
Thymidine
analog
AID
patients
Prevent
the action of viral reverse transcriptase and block DNA synthesis. Only
decrease growth not cidal. Allow person to live longer
Prevent systheis of reverse
transcriptase
Interferon ( natural substance)
A
carbohydrate containing protein
Naturally
produced by fibroblast and leukocytes in the infected cells
Initial
cell is killed; however that cells will produce interferon to protect other
cells from infection.
Side
Effect
1-
Tissue damage through toxicity (stop function of the cell membrane)
2-
Allergic reaction (based on the person)
3-
Disruption in the balance of normal microbial flora (good bacteria that lives
inside our body, don’t allow bad bacteria in, unless there is a problem)
Contact,
Infection and Disease
Extra information about Antimicrobial Drug
Antibiotics: antimicrobial agents produced by microorganisms
that kill or inhibit other microorganisms. This is the microbiologist's
definition. A more broadened definition of an antibiotic includes any chemical
of natural origin (from any type of cell) which has the effect to kill or
inhibit the growth of other types cells. Since most clinically-useful
antibiotics are produced by microorganisms and are used to kill or inhibit
infectious Bacteria, we will follow the classic definition.
Antibiotics are low molecular-weight (non-protein) molecules
produced as secondary metabolites, mainly by microorganisms that live in the
soil. Most of these microorganisms form some type of a spore or other dormant
cell, and there is thought to be some relationship (besides temporal) between
antibiotic production and the processes of sporulation. Among the molds, the
notable antibiotic producers are Penicillium and Cephalosporium , which are the
main source of the beta-lactam
antibiotics (penicillin and its relatives). In the Bacteria,
the Actinomycetes, notably Streptomyces species, produce a variety of types of
antibiotics including the aminoglycosides (e.g. streptomycin), macrolides (e.g.
erythromycin), and the tetracyclines. Endospore-forming Bacillus species produce
polypeptide antibiotics such as polymyxin and bacitracin. The table below
(Table 4) is a summary of the classes of antibiotics and their properties
including their biological sources.
Table 4. Classes of
antibiotics and their properties
________________________________________________________________________
Biological
source
Spectrum
(Effective against)
Mode
of action
____________________________________________________________________________________________________________
Beta-lactams (penicillins
and
cephalosporins)
Penicillin G,
Cephalothin
Penicillium
notatum and
Cephalosporium
Gram-positive
bacteria
Inhibits steps in cell wall (peptidoglycan)
synthesis
and murein assembly
Semisynthetic
penicillin
Ampicillin,
Amoxycillin
Gram-positive and
Gram-negative
bacteria
Inhibits steps in
cell wall
(peptidoglycan)
synthesis
and
murein assembly
Clavulanic Acid
Clavamox is
clavulanic acid
plus amoxycillin
Streptomyces
clavuligerus
Gram-positive and
Gram-negative
bacteria
Suicide inhibitor of
beta-lactamases
Monobactams
Aztreonam
Chromobacter
violaceum
Gram-positive and
Gram-negative bacteria
Inhibits steps in
cell wall
(peptidoglycan)
synthesis and
murein
assembly
Carboxypenems
Imipenem
Streptomyces
cattleya
Gram-positive and
Gram-negative bacteria
Inhibits steps in cell wall (peptidoglycan) synthesis and
murein assembly
____________________________________________________________________________________________________________
________________________________________________________________________
Biological
source
Spectrum
(Effective against)
Mode of action
____________________________________________________________________________________________________________
Aminoglycosides
Streptomycin ( Streptomyces
Griseus)
Gram-positive and
Gram-negative
bacteria
Inhibit translation
(protein synthesis)
Gentamicin
(Micromonospora
species)
Gram-positive and
Gram-negative
bacteria esp.
Pseudomonas
Inhibit translation
(protein synthesis)
Glycopeptides
Vancomycin
(Streptomyces
orientales)
Gram-positive
bacteria, esp.
Staphylococcus
aureus
Inhibits steps in
murein
(peptidoglycan)
biosynthesis and
assembly
Lincomycins
Clindamycin
(Streptomyces
lincolnensis)
Gram-positive and
Gram-negative
bacteria esp.
anaerobic
Bacteroides
Inhibits translation
(protein synthesis)
Macrolides
Erythromyci
(Streptomyces
erythreus) Gram-positive
bacteria,
Gram-negative
bacteria
not
enterics, Neisseria,
Legionella,
Mycoplasma
Inhibits translation
(protein synthesis)
Polypeptides
Polymyxin
( Bacillus polymyxa)
Gram-negative
bacteria
Damages
cytoplasmic
membranes
____________________________________________________________________________________________________________
Biological
source
Spectrum
(Effective against)
Mode
of action
____________________________________________________________________________________________________________
Bacitracin
(Bacillus
subtilis)
Gram-positive
bacteria
Inhibits steps in
murein
(peptidoglycan)
biosynthesis and
assembly
Polyenes
Amphotericin
(Streptomyces
nodosus)
Fungi
Inactivate
membranes
containing sterols
Nystatin
(Streptomyces
noursei)
Fungi (Candida)
Inactivate
membranes
containing sterols
Rifamycins
Rifampicin
(Streptomyces
mediterranei)
Gram-positive and
Gram-negative
bacteria,
Mycobacterium
tuberculosis
Inhibits
transcription
(eubacterial RNA
polymerase)
Tetracyclines
Tetracycline
(Streptomyces
species)
Gram-positive and
Gram-negative
bacteria,
Rickettsias
Inhibit
translation
(protein synthesis)
Semisynthetic
tetracycline
Doxycycline
Gram-positive and
Gram-negative
bacteria,
Rickettsias
Ehrlichia, Borellia
Inhibit
translation
(protein synthesis)
Chloramphenicol
Chloramphenicol
(Streptomyces
venezuelae)
Gram-positive and Gram-negative bacteria Inhibits translation (protein synthesis)
___________________________________________________________________________________________________________
(
Antimicrobial Agents Used in the Treatment of
Infectious Disease
The modern era of antimicrobial chemotherapy began
in 1929 with Fleming's discovery of the
powerful bactericidal substance penicillin, and
Domagk's discovery in 1935 of synthetic chemicals
(sulfonamides) with broad antimicrobial activity. In
the early 1940's, spurred partially by the need for
antibacterial agents in WW II, penicillin was
isolated, purified and injected into experimental animals,
where it was found to not only cure infections but
also to possess incredibly low toxicity for the
animals. This fact ushered into being the age of
antibiotic chemotherapy and an intense search for
similar antimicrobial agents of low toxicity to
animals that might prove useful in the treatment of
infectious disease. The rapid isolation of
streptomycin, chloramphenicol and tetracycline soon
followed, and by the 1950's, these and several other
antibiotics were in clinical usage.
The most important property of a clinically-useful
antimicrobial agent, especially from the patient's
point of view, is its selective toxicity, i.e., that
the agent acts in some way that inhibits or kills
bacterial pathogens but has little or no toxic
effect on the animal taking the drug This implies that the
biochemical processes in the bacteria are in some
way different from those in the animal cells, and
that the advantage of this difference can be taken
in chemotherapy. Antibiotics may have a cidal
(killing) effect or a static (inhibitory) effect on
a range of microbes. The range of bacteria or other
microorganisms that are affected by a certain
antibiotic are is expressed as its spectrum of action.
Antibiotics effective against procaryotes which kill
or inhibit a wide range of Gram-positive and
Gram-negative bacteria are said to be broad spectrum
. If effective mainly against Gram-positive or
Gram-negative bacteria, they are narrow spectrum .
If effective against a single organism or
disease, they are referred to as limited spectrum.
Kinds of Antimicrobial Agents and their Primary
Modes of Action
1. Cell wall synthesis inhibitors Cell wall
synthesis inhibitors generally inhibit some step in the
synthesis of bacterial peptidoglycan. Generally they
exert their selective toxicity against eubacteria
because human cells lack cell walls.
Beta lactam antibiotics Chemically, these
antibiotics contain a 4-membered beta lactam ring. They
are the products of two groups of fungi, Penicillium
and Cephalosporium molds, and are
correspondingly represented by the penicillins and
cephalosporins. The beta lactam antibiotics inhibit
the last step in peptidoglycan synthesis, the final
cross-linking between between peptide side chains,
mediated by bacterial carboxypeptidase and
transpeptidase enzymes . Beta lactam antibiotics are
normally bactericidal and require that cells be
actively growing in order to exert their toxicity.
Natural penicillins, such as Penicillin G or
Penicillin V, are produced by fermentation of
Penicillium chrysogenum. They are effective against
streptococcus, gonococcus and staphylococcus,
except where resistance has developed. They are
considered narrow spectrum since they are not
effective against Gram-negative rods.
Semisynthetic penicillins first appeared in 1959. A
mold produces the main part oif the molecule
(6-aminopenicillanic acid) which can be modified
chemically by the addition of side shains. Many of
these compounds have been developed to have distinct
benefits or advantages over penicillin G,
such as increased spectrum of activity
(effectiveness against Gram-negative rods), resistance to
penicillinase, effectiveness when administered
orally, etc. Amoxycillin and Ampicillin have
broadened spectra against Gram-negatives and are
effective orally; Methicillin is
penicillinase-resistant.
Clavulanic acid is a chemical sometimes added to a
semisynthetic penicillin preparation. Thus,
amoxycillin plus clavulanate is clavamox or
augmentin. The clavulanate is not an antimicrobial
agent. It inhibits beta lactamase enzymes and has
given extended life to penicillinase-sensitive beta
lactams.
Although nontoxic, penicillins occasionally cause
death when administered to persons who are
allergic to them. In the U.S.
individuals the beta lactam molecule attaches to a
serum protein which initiates an IgE-mediated
inflammatory response.
Cephalolsporins are beta lactam antibiotics with a
similar mode of action to penicillins that are
produced by species of Cephalosporium. The have a
low toxicity and a somewhat broader spectrum
than natural penicillins. They are often used as
penicillin substitutes, against Gram-negative bacteria,
and in surgical prophylaxis. They are subject to
degradation by some bacterial beta-lactamases, but
they tend to be resistant to beta-lactamases from S.
aureus .
Bacitracin is a polypeptide antibiotic produced by
Bacillus species. It prevents cell wall growth by
inhibiting the release of the muropeptide subunits
of peptidoglycan from the lipid carrier molecule that
carries the subunit to the outside of the membrane
Teichoic acid synthesis, which requires the same
carrier, is also inhibited. Bacitracin has a high
toxicity which precludes its systemic use. It is present
in many topical antibiotic preparations, and since
it is not absorbed by the gut, it is given to "sterilize"
the bowel prior to surgery.
2. Cell membrane inhibitors disorganize the
structure or inhibit the function of bacterial
membranes. The integrity of the cytoplasmic and
outer membranes is vital to bacteria and
These drugs disorganize the membranes rapidly and
kill the cells. However, due to the similarities in phospholipids in bacterial
and eukaryotic membranes, this action is rarely specific enough to permit these
compounds to be used systemically. The only antibacterial antibiotic of
clinical
importance that acts by this mechanism is Polymyxin,
produced by Bacillus polymyxis. Polymyxin is effective mainly against
Gram-negative bacteria and is usually limited to topical usage.
Polymyxins bind to membrane phospholipids and
thereby interfere with membrane function. Polymyxin is occasionally given for
urinary tract infections caused by Pseudomonas that gentamicin, carbenicillin
and tobramycin resistant. The balance between effectiveness and damage to the
kidney and other organs is dangerously close, and the drug should only be given
under close supervision in the hospital.
3. Protein synthesis inhibitors:
Many therapeutically useful antibiotics owe their
action to inhibition of some step in the complex process of translation. Their
attack is always at one of the events occurring on the ribosome and rather than
the stage of amino acid activation or attachment to a particular tRNA. Most
have an affinity or specificity for 70S (as opposed to 80S) ribosomes, and they
achieve their selective toxicity in this manner. The most important antibiotics
with this mode of action are the tetracyclines, chloramphenicol, the macrolides
(e.g. erythromycin) and the
aminoglycosides (e.g. streptomycin).
The aminoglycosides are products of Streptomyces
species and are represented by streptomycin, kanamycin, tobramycin and
gentamicin. These antibiotics exert their activity by binding to bacterial
ribosomes and preventing the initiation of protein synthesis. Aminoglycosides
have been used against
a wide variety of bacterial infections caused by
Gram-positive and Gram-negative bacteria.
Streptomycin has been used extensively as a primary
drug in the treatment of tuberculosis.
Gentamicin is active against many strains of
Gram-positive and Gram-negative bacteria, including some strains of Pseudomonas
aeruginosa. Kanamycin (a complex of three antibiotics, A, B and C)
is active at low concentrations against many
Gram-positive bacteria, including penicillin-resistant
staphylococci. Gentamicin and Tobramycin are
mainstays for treatment of Pseudomonas infections.
An unfortunate side effect of aminoglycosides has
tended to restrict their usage: prolonged use is
known to impair kidney function and cause damage to
the auditory nerves leading to deafness.
The tetracyclines consist of eight related
antibiotics which are all natural products of Streptomyces,
although some can now be produced semisynthetically.
Tetracycline, chlortetracycline and
doxycycline are the best known. The tetracyclines
are broad-spectrum antibiotics with a wide range
of activity against both Gram-positive and
Gram-negative bacteria. The tetracyclines act by blocking
the binding of aminoacyl tRNA to the A site on the
ribosome. Tetracyclines inhibit protein synthesis
on isolated 70S or 80S (eukaryotic) ribosomes, and
in both cases, their effect is on the small
ribosomal subunit. However, most bacteria possess an
active transport system for tetracycline that
will allow intracellular accumulation of the
antibiotic at concentrations 50 times as great as that in the
medium. This greatly enhances its antibacterial
effectiveness and accounts for its specificity of action,
since an effective concentration cannot be
accumulated in animal cells. Thus a blood level of
tetracycline which is harmless to animal tissues can
halt protein synthesis in invading bacteria.
The tetracyclines have a remarkably low toxicity and
minimal side effects when taken by animals.
The combination of their broad spectrum and low
toxicity has led to their overuse and misuse by the
medical community and the wide-spread development of
resistance has reduced their effectiveness.
Nonetheless, tetracyclines still have some important
uses, such as in the treatment of Lyme disease.
Chloramphenicol has a broad spectrum of activity but
it exerts a bacteriostatic effect. It is effective
against intracellular parasites such as the
rickettsiae. Unfortunately, aplastic anemia, which is dose
related develops in a small proportion (1/50,000) of
patients. Chloramphenicol was originally
discovered and purified from the fermentation of a
Streptomyces, but currently it is produced entirely
by chemical synthesis. Chloramphenicol inhibits the
bacterial enzyme peptidyl transferase thereby
preventing the growth of the polypeptide chain
during protein synthesis.
Chloramphenicol is entirely selective for 70S
ribosomes and does not affect 80S ribosomes. Its
unfortunate toxicity towards the small proportion of
patients who receive it is in no way related to its
effect on bacterial protein synthesis. However,
since mitochondria probably originated from
procaryotic cells and have 70S ribosomes, they are
subject to inhibition by some of the protein
synthesis inhibitors including chloroamphenicol.
This likely explains the toxicity of chloramphenicol.
The eukaryotic cells most likely to be inhibited by
chloramphenicol are those undergoing rapid
multiplication, thereby rapidly synthesizing
mitochondria. Such cells include the blood forming cells of
the bone marrow, the inhibition of which could
present as aplastic anemia. Chloramphenicol was
once a highly prescribed antibiotic and a number of
deaths from anemia occurred before its use was
curtailed. Now it is seldom used in human medicine
except in life-threatening situations (e.g. typhoid
fever).
The Macrolides are a family of antibiotics whose
structures contain large lactone rings linked
through glycoside bonds with amino sugars. The most
important members of the group are
erythromycin and oleandomycin. Erythromycin is
active against most Gram-positive bacteria,
Neisseria, Legionella and Haemophilus, but not
against the Enterobacteriaceae. Macrolides
inhibit bacterial protein synthesis by binding to
the 50S ribosomal subunit. Binding inhibits elongation
of the protein by peptidyl transferase or prevents
translocation of the ribosome or both. Macrolides
are bacteriostatic for most ba
Bacterial metabolism:
Bacterial
Interaction:
Body
surfaces are in constant contact with microorganisms
Normal
flora: Microorganisms implanted in a tissue as Colonists
Transient:
Microorganisms that is rapidly lost
Infection:
Condition in which pathogenic microorganisms penetrate the host defense and enter
the tissues and multiply
Infectious:
Microorganisms that invade the tissue and lead to infection.
Disease-
malfunction of a tissue or organ caused by microbes or their product
Contaminant-
Presence of infectious agent in the tissue with out yet invading it.
Morbidity-
Damaged tissues and organs may lead to dysfunction
Mortality-
Damage may be enough to cause death
Resident
Flora:
(ndigenous
Flora- Microflora- Microbiola- Amphibionts,Associate-) The large and mixed
collection of microbe adapted to the body
Microflora
consists of bacteria, fungi, protpzoa, and to certain extent virus and
arthopodes
Sites
that harbor normal flora:
1-
Skin
2-
Uppder repiratory
tract
3-
Alimentary canal
4-
Other opening of
urethra
5-
External
genitalia
6-
Vagina
7-
External ear
canal
8-
External eye (
lid, conjunctiva)
Flora
of the mouth
Most
diverse and adundant of the body.
Aerobic
streptococci
Cheeks
epitherlium, tongue, floor of the mouth, tooth, provide numerous niches for
hundres of diffrene species to colonize
The
process of Infection:
Microbe
enter the body,
cross
host barrier,
multiplies
in large tissue and
release
to exterior ( exit )
The
portal of entry-initiation of infection
Cutaneous
and/ or membranous boundary are route for entry. portal entries are the same as
anatomicalo site for normal flora
Ex
Skin, alimentary tract respiratory tract, and urogenital tract
One
or two specified portal entry for each microorgamisn
Ex.
flue- nasal inoculation ---- infection
-
skin inoculation---- no infection
The
Source of Infectious Agents
1-
Exogenous
2-
Endogenous
The
Size of Inoculation
Minimum number of microorgamism required to initatie and infection called infectious dose (ID)
Minimum number of microorgamism required to initatie and infection called infectious dose (ID)
The
quantity varied between 1-10 (9) cells
Pathogenicity
and Virulence Factors:
Pathogenicity-
microbial effectivemess
Virulence-
microvial invasivemess and toxigenicity
Virulence
factor- the properties which contribute to ap pathogen capacity to infect and
damage host tissue
Pathogenicity:
The
capacity of a microorgamisn to cuasues infection or disease
Pathogenic
microbe:
True
Pathogens (primany pathogens) are capable of causing infection and disease in
healthy persons with noramal immune defenses.
Opportunistic
pathogens (secondary pathogen) infect persons whose host defensed ( immunites
are compromised
Factors
that increase the risk of opportunistic infectins are as follow:
Old
age, extreme youth, malnutrition, genetic defect in immunity, acquired effects
inimminity ( AIDS), cancer, chemot
Mechanism
of Invasion and Tissue damage
A.
Attachment
Adhesion- Process by which microbe gain a more stable
foothold at the portal of entry.
The
following are responsible for adhesion:
Bacteria- Pilli, Fimbria, capsule and adhesive
slime.
Virus-
Specialized receptor
Protozoa-
Organelle of locomotion
Parasitic
worm- suckers and hocks
B.
Virulence
Exoenzyme or extracellulare enzymes dissolve the host defense barrier and promote the
spread of microbes to deeper tissues
1.
Muclindse (mucinase)
Digests mucous membranes and is produced
by Vibrio cholera
2. Keratinase-
Digest the principal component of skin and hair is
produced by dermatohphytic fungi
3. Collagenase
Digest Fiber of connective tissue and is produced by
Clostridium and certain worms
4.
Hyaluroindiase
(spreading factor)-
Digest ground substance that cements
the animal celsls together and is produced by
Staphylococci, clostridia, and
streptococci
5.
Coagulase-
Causes clotting of blodd and plasma and is produced by
Staphylocci
6.
Bacterial Kinase
Causes dissolving fibrin clot and is produced by
streptokinase and staphlokinase
Bacterial Toxin:
Toxin- A specific chemical product of microbes, plants and animals that is
poisonous to other living things
Toxigenicity - The power to produce toxin.
Toxemia- spread of toxin through blood
Toxin’s name- Originate from its target of action
Neurtotoxin -act neuron cells
Introtoxin- on the intestine system;
Enterotoxin - act on the intestine track
Hemotoxin, lyse red blood cells
Nephrotoxins -damage the kidney cells
Traditional classification of toxin
How toxins are produced
Exotoxin- Toxin secreted by living bacteria cells,
outside of the cell
- Specific towards the body
-More toxic
that endotoxins
- Made of protein (protein
is heat sensitive and best stimulus for our immune system )
- Heat unstable (able to be denatured)
- Convert to toxoid (neutralized toxin, toxin without
affect)
- Stimulate antitoxins (protein is best stimuli for
immune system)
- Can cause Fever
- Secreted, no lysis
- Produced by gram positive and negative
Endotoxins-Apart of the structure of bacteria; not
released until bacteria is dead
- Made of Lippoplysaccharide
- Heat stable
- Unable to convert to toxoid
- Do not stimulate antitoxins
- Can not cause fever
- Released by lysis
- All gram negative
Exotoxin - Protein with strong specific for target
cells, and affect cells by damaging the cell membrane and causing cell lysis.
Produced by gram positive and negative, damage body
Endotoxins- Lippoplysaccharide ( Gram negative) General; toxic effect all over the body, can
have a toxic effect on all cells in the body.
Hemolysin-Disrupt the cell membrane of red blood cells
and caused the red blood cells to hemolyze (cell burse and release of
hemogloboline)
Ex. Toxins of staphylococcus aureus
Bacteremia- Presence of bacteria in the blood
Viremia- Presence of Virus in the blood
Portal of Exit:
A specific
avenue for departure of microbes
1- Respiratory and salivary portals
2- Skin Scale
3- Fecal exit
4- Urogenital tract- STD’s
5- Bleeding and removal of blood
Persistence
of Microbe:
Latency-
Change of microbe to inactive form (Latent infection), immune system can not
kill. Will become active and multiply, (only some bacteria and virus)
-
Will remain in the body for a long period of time
Recurrence-
Activation of afent and induction of disease again
Ex.
Herpes simplex, Herpes Zoster, EBV, AIDS, Syplisis, Tyhoid fever, Tuberculosis
and Malaria
Microbial Nutrition
Nutrition is a process by which all organisms
(micro/macro) obtain substances from their environment to convert to metabolic
uses.
All microorganisms require six bioelements:
Carbon
Hydrogen
Oxygen
Nitrogen
Phosphorus
Sulfur
To survive, grow and reproduce.
Microbial Nutrient
Nutrient categorized by:
A. Amount
B. Chemical
Structure
C. Importance
to the Organism
A. Amount
1. Macronutrients: Large amounts required and have
principal roles in bacterial cells structure and metabolism.
2. Microelements: Small amount required for maintenance
of bacterial structure and function.
B. Chemical Structure
1. Organic
Composed of
Carbon, and Hydrogen.
2. Inorganic
Simple molecule that is composed of other elements
beside C, and H2.
C. Importance to the organism
1. Essential
Nutrients are essential for bacterial growth and survival.
2. Non-Essential
Nutrients are not essential for bacterial growth and
survival.
Microorganisms are classified by chemical form
of their nutrient.
a. Hetrotrophs
Microorganisms obtain carbon in the form of organic
matter from the bodies of other organisms.
b. Autotrophs
Microorganisms obtain carbon from inorganic gas
(carbon dioxide) and have the special capacity to convert CO2 into
organic compounds.
Epidemiology:
Epidemiology-
The study of disease in a population
Surveillance-
Rate of occurrence, mortality,
morbidity and transmission of infections
Prevalence-
Total number of existing cases with
respect to the entire population
Incidence-
Number of new cases over a certain
time over healthy population
Endemic-
A constant number of cased during a long
period of time in a specific
geographic locale
Sporadic-
A few isolated cased in a wide spread locale (unpredictable)
Epidemic-
Prevalence of cases increased
unexpectedly, number of cases increase
Pandemic-
The spread of epidemic all over the world ex (AIDS)
MIDTERM
EXAM
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