11
MICROBIAL CHAPTER GENETICS AND INFECTIOUS
DISEASE
Dennis Kunkel
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
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ISBN: 978-0-8153-6514-3
WHY IS THIS IMPORTANT?
Understanding
genetic mechanisms lets us
study how microorganisms can mutate and
change in ways that allow them to defeat host
defenses.
These changes are one of the most important topics
in health care today.
To
understand pathogenesis and virulence, we
must be familiar with microbial genetics.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
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WHY IS THIS IMPORTANT?
Organisms
become resistant through mutations
Mutations can be transferred to other bacteria.
Transfer of these mutations can make a harmless
bacterium dangerous and a dangerous bacterium
lethal.
One of the most difficult problems in medicine
today is antibiotic resistance.
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OVERVIEW
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DNA
DNA stands
DNA is
for deoxyribonucleic acid.
a blueprint for all components of the
cell.
The blueprint can be faithfully passed on from one
generation to the next.
The structure of DNA allows replication and
transcription to be a simple process.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
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DNA STRUCTURE
DNA is a double stranded helical structure.
The two strands are complementary and
wind around each other to form the double
helix.
It is composed of nucleotides.
Each nucleotide is a phosphate, a sugar
(deoxyribose), and a nucleotide base.
The bases project inward.
The components of DNA bind together in
a very specific way.
This permits a correct and precise orientation
of the nucleotide.
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DNA STRUCTURE
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
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DNA STRUCTURE
Nucleotides
join to
each other to form a
chain.
The
3 hydroxyl group
of a sugar joins to the
5 phospahte of another
nucleotide.
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DNA STRUCTURE
DNA has
base
Purines adenine and
guanine
two types of
Purines are large doublering structures.
Pyrimidines thymine
and cytosine
Pyrimidines have smaller
single ring structures.
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DNA STRUCTURE
DNA has a helical geometry governed by how the bases
pair up.
The strands are anti-parallel.
Adenine always pairs with thymine.
Cytosine always pairs with guanine.
One of the strands is oriented upside down relative to the
other.
The bases are stacked on top of each other.
DNA is a chemically stable molecule.
Any mismatched pairing is chemically unstable.
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RNA
RNA stands
for ribose nucleic acid.
RNA differs
from DNA in several ways.
It contains the sugar ribose (rather than
deoxyribose).
It contains uracil instead of thymine.
Uracil pairs up with adenine.
It is usually found in single-stranded form.
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RNA
There
are three forms of RNA:
Messenger RNA contains information derived
from DNA
Transfer RNA carries amino acids to ribosomes
Ribosomal RNA helps maintain the proper shape
of ribosomes.
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DNA REPLICATION
This
is the process by which DNA is copied.
Bidirectional
Semiconservative
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INITIATION AND TERMINATION
OF REPLICATION
Specific proteins recognize and bind to a distinct region
of the DNA, an origin of replication on the DNA
Binding causes localized melting of a specific region
within the origin.
The enzyme primase uses the exposed single strands as
templates to synthesize small fragments of RNA to
serve as primers for DNA synthesis
Termination occurs when the entire chromosome has
been copied.
Replicated chromosomes are separated by
topoisomerase.
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DNA REPLICATION:
Separation and Supercoiling
Supercoiling
is a characteristic of helical
structures.
Strands
must be uncoiled, unwound, and
separated before replication.
This is accomplished by two enzymes:
Topoisomerase unwinds the supercoils
Helicase separates and unwinds the strands.
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DNA REPLICATION:
Requirements
There
are two requirements for replication:
An ample supply of each of the nucleotides
adenine, thymine, cytosine, and guanine
A primer:template junction
Each
single strand of DNA is a template.
A portion
of the DNA is paired with a short
piece of RNA called a primer.
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DNA REPLICATION:
Requirements
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DNA REPLICATION:
Direction
DNA replication
proceeds in only one direction.
The primer:template junction gives the DNA
polymerase a place to add the next base
Binding is between the 3end of one base and the 5
end of the next base.
Elongation
of the bases is from the 3 end
This is required for chemical stability.
The
binding of a new base uses energy released
from pyrophosphate.
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DNA REPLICATION:
Direction
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DNA POLYMERASE
DNA replication
is performed by an enzyme
called DNA polymerase.
DNA polymerase
forms new strands of DNA
using the primer:template junction as a guide.
It
works incredibly quickly.
The addition of nucleotides is in the millisecond range.
There
are several types of DNA polymerase.
They perform specific functions and work at different
speeds.
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DNA POLYMERASE: Proofreading
DNA replication is extraordinarily accurate.
There are always some mistakes mutations
Evolution relies on mutations.
During replication, an error occurs approximately once in 1010 pairings.
Proofreading takes place at the primer:template junction active
site.
Improperly paired bases are removed by an exonuclease.
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THE REPLICATION FORK
The replication fork is the site where DNA replication
is occurring.
The double helix is unwound and the strands separate.
The separated strands at the replication fork are antiparallel and are identified as:
Leading strand (continuous)
Lagging strand (discontinuous)
Both strands are replicated at the same time by the
addition of bases to the 3 end of the strand.
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THE REPLICATION FORK
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THE REPLICATION FORK
The leading strand is in the correct orientation for bases
added to the 3 end of the primer:template junction.
The lagging strand is replicated in pieces called Okazaki
fragments.
Each Okazaki fragment has its own short RNA primer.
Bases are only added to the 3 end of the primer:template junction.
It is created by an RNA polymerase called primase.
When the fragment is finished, the enzyme RNAase H
removes the primer.
The gap is filled in by DNA polymerase.
Fragments are linked together by DNA ligase.
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THE GENETIC CODE
Information
in DNA is based on a four letter
alphabet (A, T, C, G).
The genetic code employs three letter
combinations called codons that code for
specific amino acids.
There are 64 possible 3 letter combinations
Only 20 amino acids are used to make
proteins.
The genetic code is degenerate.
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THE GENETIC CODE
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THE GENETIC CODE
Three
rules govern the arrangement and use of
codons:
Codons are always read in one direction.
The message is translated in a fixed reading frame
set by the initiation codon.
There is no overlap or gap in the code.
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GENE EXPRESSION
A gene is a segment of DNA that codes for a functional
product (protein).
Gene expression is the production of the functional
product.
There are two parts to gene expression:
Transcription construction of RNA from a DNA template
Translation construction of the protein using RNA
instructions.
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TRANSCRIPTION
The process by which RNA is made from a DNA
template.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
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TRANSCRIPTION
Transcription
Initiation a DNA sequence called the promoter
initially binds the RNA polymerase:
This produces a bubble in the DNA.
Elongation RNA polymerase unwinds strands of
DNA and RNA bases are added to the 3 end of the
growing strand of RNA
has three steps:
It also re-anneals the strands.
Termination a sequence of DNA (terminator) signals
the end of transcription:
RNA polymerase detaches from DNA
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TRANSCRIPTION
coding strand (+)
3
5
template strand (-)
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TRANSCRIPTION: Summary
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TRANSLATION
This
is the process by which proteins are made
The sequence of nucleotides in messenger RNA is
translated into a sequence of amino acids.
It is directly affected by any errors in either DNA or
RNA.
Translation
requires all three types of RNA
messenger, transfer, and ribosomal.
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MESSENGER RNA (mRNA) IN
TRANSLATION
Encodes
proteins
An open reading frame (ORF) indicates the start
of an amino acid sequence.
An ORF begins with a start codon.
Translation moves from the 5end to the 3 end.
An ORF ends with a stop codon.
mRNA contains
a sequence of nucleotides serving
as a binding site for the ribosomal subunits.
Ribosome and mRNA bind here through
complementary base pairing.
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TRANSFER RNA (tRNA) IN
TRANSLATION
tRNA molecules function as adapters between
mRNA attached to a ribosome and the amino acids
being added to the growing protein chain
Each tRNA attaches to a specific amino at the
acceptor arm and to a specific codon in the mRNA
Every tRNA ends with the codon 3-CCA-5
Site at which the amino acids are coupled to
the tRNA by the enzyme aminoacyl-tRNA
synthetase
Each tRNA is specific for only one amino acid
It brings amino acids to the ribosome.
It binds to the ribosome at the anti-codon region
using complementary base pairing.
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THE RIBOSOME IN
TRANSLATION
The ribosome is composed of three
molecules of rRNA and over 50
proteins.
It adds amino acids at a rate of 2-20
amino acids per second
In prokaryotes, the ribosome
attaches to mRNA as the mRNA is
being made
More than one ribosome can move
along the same messenger RNA
This is called a polyribosome or
polysome.
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PROKARYOTIC RIBOSOME
Contains
the machinery that directs protein
synthesis
Two subunits (made up of rRNA and
proteins)
50S (large): peptide bond formation
30S (small): decoding center, where tRNA binds
to the mRNA
Total
mass is 70S (S=Svedberg
units, a measurement of the
mass of the subunits)
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FORMATION OF PEPTIDE
BONDS IN TRANSLATION
Proteins are composed of sequences of
amino acids linked to one another by
peptide bonds
Peptide bonds form between amino
acids while on the ribosome (peptidyl
transferase reaction).
The ribosome has 3 binding sites for
tRNA:
A site tRNA brings in new amino acid
P site tRNA holds the growing amino
acid chain (peptidyl-tRNA)
E site tRNA exits the ribosome.
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STAGES OF TRANSLATION
There
are three stages of transcription:
Initiation
Elongation
Termination
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INITIATION
Initiation
requires:
Recruitment of the
ribosome to the mRNA
Placement of a methionine
tRNA complex at the P site
Precise positioning of the
ribosome over the start
codon of mRNA.
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ELONGATION
After
initiation, three things must occur in order
for amino acids to be added to methionine.
A tRNA carrying the next amino acid is loaded into the
A site.
A peptide bond forms between the amino acids.
Each tRNA moves the one at the A site to the P site,
the one at the P site to the E site.
The
ribosome moves along the messenger RNA.
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TERMINATION
Translation
continues until a
stop codon enters the A site.
Stop codons are recognized
by specialized proteins.
These specialized proteins
cause the translation complex
to fall apart.
The
peptide chain is
released from the ribosome
and begins to form
secondary and tertiary
structures.
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REGULATION OF GENE
EXPRESSION
Protein
synthesis is energetically expensive
and highly regulated.
Some genes are always turned on constitutive
genes.
Some genes are on and can be turned off
repressible genes.
Some genes are off and can be turned on
inducible genes.
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REGULATION OF GENE
EXPRESSION
Gene expression is controlled by regulatory proteins
that bind DNA:
Activators involved in positive regulation (induction)
Repressors involved in negative regulation (repression)
Regulatory proteins recognize two adjacent sites on
DNA near the genes they control.
The promoter site where RNA polymerase binds
The operator site where regulatory proteins bind
When the operator is occupied the RNA polymerase cannot
bind to the promoter, thereby inhibiting transcription and
gene expression.
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INDUCTION
Induction
turns on genes that are off
(repressed).
The
best example is the lactose operon (lac
operon):
Code for enzymes that enable bacteria to utilize the
sugar lactose.
lac operon is normally off.
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lac Operon
lacI: lac repressor
lacZ: -galactosidase, cleaves
lactose into galactose and glucose
lacY: permease membrane
transport protein for lactose
lacA: transacetylase, rids the cell
of toxic by-products of galactose
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lac Proteins
The
lac has system two regulatory proteins that
bind at or near the operator site on DNA.
The lac repressor
The lac activator - CAP (catabolite activator
protein).
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OPERATION OF THE lac OPERON
The
lac repressor is
expressed constitutively.
It
binds at the operator site
and overlaps part of the
promoter site
This blocks the RNA
polymerase and CAP from
binding.
This prevents transcription
of the lac operon.
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EXPRESSION OF lac OPERON
For the genes of the lac
operon to be turned on, the
repressor must first be
inhibited.
CAP-cAMP complex then
recruits RNA polymerase.
lac operon is transcribed.
cAMP
CAP binds cAMP (when
glucose is absent high
cAMP levels)
CAP
When cAMP levels fall, no
complex is formed.
RNA polymerase does not
bind to the promoter site.
The lac genes are not
expressed.
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EXPRESSION OF lac OPERON
The
expression of lac genes is leaky
A few transcripts are made and there is always a
low level of -galactosidase.
This allows small amounts of lactose into the cell.
Lactose is converted to allolactose.
Allolactose binds the lac repressor.
This changes the shape of the lac repressor and it
can no longer bind the operator site.
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REPRESSION
There are also cellular mechanisms that turn off (repress) genes.
This is very important for the conservation of energy.
A good example of repression is the synthesis of tryptophan.
Tryptophan is made until it begins to accumulate in excessive
amounts.
Tryptophan becomes a co-repressor of its own synthesis.
The cell produces a tryptophan repressor (always produced) but cannot
bind DNA in its normal form.
Excess tryptophan binds the repressor and changes its shape so it can
bind DNA and repress the production of tryptophan.
When tryptophan decreases it no longer binds the repressor. The
repressor can no longer bind DNA and tryptophan is again produced.
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TRYPTOPHAN OPERON
Encode enzymes needed for
synthesis of the amino acid
tryptophan
trp
repressor
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TRYPTOPHAN OPERON
Low tryptophan levels, transcription occurs
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TRYPTOPHAN OPERON
High tryptophan levels, repression occurs
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MUTATION & REPAIR OF DNA
Mutations are changes in the DNA sequence.
Spontaneous mutations are those that occur in the cells natural
environment.
The chances that any single gene will undergo a mutation when one
cell divides into two are between one on 10,000 (10-4) and one in a
trillion (10-12).
Mutations allow organisms to respond to a changing environment.
A spontaneous mutation to antimicrobial resistance will result in the mutant
becoming the dominant organism in a hospital environment where the
antimicrobial medication is present. The antimicrobial kills the sensitive
cells and thereby allows the resistant cells to take over the population.
Change in DNA sequence can cause changes in proteins.
Mutations must be kept to a minimum.
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BASE SUBSTITUTIONS
Base substitution: when an incorrect base is incorporated into DNA during
DNA synthesis.
If one base pair is changed the mutation is called a point mutation.
Three possibilities:
Silent mutation: occurs when a
nucleotide change generates a codon
that still specifies the wild type amino
acid
Missense mutation: occurs when
the new codon specifies a different
amino acid
Nonsense mutation: occurs when the
new codon is a stop codon, resulting in
a shortened, or truncated protein
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Removal or Addition of Nucleotides
Deletion or addition of nucleotides,
which may occur in the course of
DNA replication, is another type of
spontaneous mutation.
If three nucleotides are deleted or
added this removes or adds one codon
from the DNA.
Adding or substracting one or two
nucleotides is more significant
because it causes a frameshift
(changes the reading frame).
Suppressor mutations can reverse the
primary mutation.
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MUTATION & REPAIR OF DNA
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INDUCED MUTATIONS
Mutagen: chemicals or radiation that can increase the frequency of
mutations at least 1,000-fold
Chemical mutagens:
Chemical Modification of Purines and Pyrimidines
Base Analogs
Compounds that structurally resemble purine or pyrimidine bases closely enough that they can be
mistakenly incorporated in place of the natural bases as nucleotides are synthesized (5bromouracil, 2-amino purine)
Intercalating Agents
Alkylating agents: highly reactive chemicals that add alkyl groups onto purines and pyrimidines,
altering their hydrogen-bonding properties (nitrosoguanidine, nitrous acid, )
Do not alter hydrogen-bonding properties of the bases; rather, they insert, or intercalate, between
adjacent base pairs in one of the strands of DNA.
Pushes the nucleotides apart, producing enough space between spaces that errors are made during
replication (ethidium bromide)
Frameshift mutation
Radiation
Ultraviolet Irradiation: causes covalent bond formation between adjacent thymine
molecules on the same strand of DNA (thymine dimers).
The major mutagenic action of UV light results from the cells repairing the damage by a
mechanism termed SOS repair.
X Rays: cause several types of damage: single- and double-strand breaks in DNA, and
alterations to the bases
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COMMON MUTAGENS
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REPAIR OF DNA DAMAGE
Removal
and repair of altered bases
Mechanisms of DNA repair:
Excision repair: corrects damage that causes
distortions in the double helix
Nucleotide excision repair
Base excision repair
Direct repair
Photoreactivation
SOS Response
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NUCLEOTIDE EXCISION
REPAIR
Can remove thymine dimers and repair
almost any other injury that produces a
detectable distortion in DNA.
Involves the repair enzyme (UvrABC
endonuclease).
The UvrAB complex tracks along the
DNA in search of damaged DNA. After
damage is detected, UvrA is released and
UvrC binds.
UvrC makes cuts on both sides of the
thymine dimers.
Damaged nucleotides and a few
nucleotides on either side of the lesion are
removed.
DNA polymerase fills in the resulting
single-stranded gap.
DNA ligase joins the fragments.
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BASE EXCISION
Employs DNA glycosylases to
remove damaged or unnatural
bases yielding apurinic or
apyrimidinic (AP) sites.
AP endonucleases recognize the
damaged DNA and nick the
backbone at the AP site
DNA polymerase I removes the
damaged region, using its 5 to 3
exonuclease activity.
It then fills in the gap, and DNA
ligase joins the DNA fragments.
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PHOTOREACTIVATION
Photoreactivation repairs thymine dimers by splitting
them apart with the help of visible light.
It is accomplished by an enzyme called photolyase.
Photolyase binds to the dimer in the dark.
Photolyase is activated by light and breaks the thyminethymine bond.
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SOS RESPONSE
If DNA is heavily damaged by UV light such that it
contains many thymine dimers, photoreactivation and
excision repair may not be able to correct all of the
dimers and the cells will die.
The SOS response bypasses the damaged DNA and
allows replication to continue.
Involves a special DNA polymerase that makes many
mistakes and incorporates the wrong bases in the
DNA strand it is synthesizing.
No proofreading ability
As a result, mutations arise
Cell survives but numerous mutations are generated
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TRANSFER OF GENETIC
INFORMATION
Bacteria
can shuffle genes.
This is called genetic recombination.
There
are four ways in which genetic
recombination can occur:
Transposition within the same bacterial cell
Transformation from one bacterium to another
Conjugation from one bacterium to another
Transduction from one bacterium to another
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TRANSPOSITION
Transposition
is caused by transposons (also
referred to as transposable elements or jumping
genes).
Transposons are pieces of DNA that can move and
integrate into different sites in the chromosome, or to a
plasmid, or vice versa.
The gene into which a transposon inserts no longer
encodes a functional protein because the insertion
disrupts the gene (insertional inactivation).
Transposons provide a mechanism for mobilizing
genes for transfer.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSPOSONS
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSPOSITION
Transposition
causes random rearrangements.
The results can be beneficial or detrimental.
Beneficial changes will be selected for and
maintained.
They may be the reason for several human
diseases.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSFORMATION
Transformation
involves the transfer of genetic
material between cells.
Uptake
by a cell of DNA, either a plasmid or a
fragment of linear DNA
It
involves naked DNA.
This DNA is taken up by a bacterial cell and
recombines with genes of that cell.
Traits that are encoded on these DNA pieces can
become part of the recipient cells genetic repertoire.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSFORMATION
The
recipient cell must be competent.
Must be able to take up large molecules such as
pieces of DNA.
Some bacteria are naturally competent, whereas
others can become competent after chemical
treatment.
Only a small amount of DNA is actually taken up.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSFORMATION:
the Griffith Experiments
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
TRANSDUCTION
Transduction involves the transfer of genetic material
between cells.
It is a common event in both Gram-positive and Gramnegative bacteria.
It uses a bacterial virus (bacteriophage or phages) for
transfer.
Recombination of the new DNA into the recipient host
chromosome
There are two forms of transduction:
Generalized any bacterial gene can be transferred
Specialized only a few specific genes can be transferred
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
GENERALIZED
TRANSDUCTION
Any
genes of the donor cell can be transferred.
It results from an error during construction of the
phage inside the infected cell; a fragment of
bacterial DNA is mistakenly substituted for phage
DNA within the protein coat (transducing particle).
Transducing particle will attach to a bacterium and
inject the nucleic acid into that cell.
Inside the cell, the injected DNA recombines with
the host chromosome.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
GENERALIZED TRANSDUCTION
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
SPECIALIZED TRANSDUCTION
During specialized transduction:
Only a few specific genes can be transferred and is carried out only by temperate phages
phage integrates only at specific sites in the chromosome of E. coli
phage incorporates its DNA into the host chromosome (prophage).
transduces specific genes by the following means:
Phage DNA excises itself from the host chromosome.
On rare occasions, part of the bacterial DNA is taken along and a piece of phage DNA is left behind.
Bacterial DNA is incorporated into viral particle creating a defective phage.
Infected bacterium lyses and releases the viral particles
Some containing donor bacterial DNA
When the defective phage infects another bacterial cell, the original host DNA is incorporated into the
next host chromosome.
Only bacterial genes located near the site of integration of the phage DNA can be
transduced.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
SPECIALIZED TRANSDUCTION
Generalized
Transduction
Specialized
Transduction
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION
Conjugation
involves the transfer of material
between cells.
Conjugation
requires direct contact between the
donor and recipient cells.
Occurs in both Gram-positive and Gram-negative
bacteria, but will only discuss Gram-negative bacteria.
DNA moves
from the donor to recipient cell
through a bacterial sex pilus on the donor cell.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION
Dennis Kunkel
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION: Plasmid Transfer
F (fertility) plasmid of E. coli, encodes the F pilus (sex pilus)
F+ cells carry the plasmid; F- cells do not
There are fours steps in conjugation:
1) The F pilus of the donor cell recognizes specific receptors on the cell
wall of recipient cell.
2) A plasmid-encoded enzyme, an endonuclease, in the donor cell cleaves
one strand of the plasmid at a specific sequence, the origin of transfer.
3) One of the two single strands of the F plasmid with the attached
endonuclease enters the F- cell and the other stays in the donor cell.
4) Complementary strands to the single-stranded DNA in the recipient
and donor cell are synthesized.
Both the donor and recipient cells are now F+ and can act as donors
of the F plasmid.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION: Plasmid Transfer
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION
Conjugation
can have several outcomes for the
recipient cell:
The plasmid can remain as a plasmid.
The plasmid can become incorporated into the
recipient cell chromosome.
When this happens, the recipient cell is then referred to
as Hfr (high frequency of recombination).
DNA from Hfr can be moved into a new recipient.
This replaces sections of the host chromosome.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
CONJUGATION-Transfer of
Chromosomal DNA
Hfr Formation
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
GENETIC TRANSFER: Summary
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3
GENETICS AND
PATHOGENICITY
Many
genetic mechanisms are involved in making
pathogens more dangerous.
Mutations
cause antibiotic resistance.
Genetic transfer is closely associated with
pathogenicity and virulence.
It transfers virulence genes into bacteria that were
previously harmless.
Genes
for antibiotic resistance and toxins are
found on plasmids.
Microbiology: A Clinical Approach, y Tony Srelkauskas Garland Science
Approach b Garland Science
ISBN: 978-0-8153-6514-3