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Lecture 1

BIOL 4215 Lecture Notes - Lecture 1: Transposase, Transposable Element, Exotoxin


Department
Biological Sciences
Course Code
BIOL 4215
Professor
W.Doerrler
Lecture
1

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Bacterial Disease exam 1
Other ways (beside food) to catch a bacterial infection:
Via aerosols in the air – Legionella or Tuberculosis
or
Go to a hospital or share a locker room - Staphylococcus aureus
or
get bitten by a tick causing Lyme disease- Borrelia burgdorferi
The ongoing battle: Man vs. pathogen
Man: innate immunity, complement immunity, humoral immunity
Barriers: skin, nasal, etc
Pathogen: endotoxin, exotoxin, effectors, drug resistance
When the bacterial protein is secreted and goes to the host cell and target protein there are possible
outcomes:
Host cell killed directly
Inhibition of host protein
Destruction of host protein
Mimic host protein
This can cause:
Alteration of signal transduction
Cell death
Immune system dysfunction
Running out of effective antibiotics
The advantage to targeting
bacterial virulence instead of
the bacteria themselves is that
it is not necessary to kill
bacteria and removes the
selective pressure that leads to
the development of antibiotic
resistance.
Also avoids collateral damage
to our microbiomes
Robert Koch
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Koch’s postulates: . Four criteria that were established by Robert Kochto identify the causative
agent of a particular disease
(1) The microbe must be consistently shown to be present
in the diseased tissue and not in healthy tissue.
Exception: Example is Borrelia burgdorferi in Lyme disease.
Sometimes there are asymptomatic carriers.
(2) The microbe must be isolated and grown in culture in pure form.
Exception: Difficult to culture some organisms
(3) The pure culture must be shown to induce the disease anew.
Exception: Must rely on animal/cell culture model
(4) reisolate organism from intentionally infected animal.
Typhoid mary- Mary Mallon asymptomatic carrier of typhoid and infected those she cooked for by fecal
oral route.
Definitions
Infection: Colonization of the body by an organism
capable of causing disease.
Disease: Infection that causes symptoms.
Colonization: Bacteria occupies and multiplies in the human body.
Carrier: infected but asymptomatic.
Virulence: ability of bacteria to cause disease.
Virulence factor: gene/protein required for disease.
We can extend Koch’s postulates to account for molecular causes of bacterial diseases (as proposed
by Stanley Falkow):
1. Genes must be associated with pathogens. Not found in avirulent strain.
2. Removal of virulence gene by mutation results in avirulent phenotype.
3. Expression of virulence gene or genes in avirulent organism
should result in virulent phenotype.
How to use this new set of postulates to identify molecular causes of pathogenesis?
1. Comparison of genomes from pathogenic and nonpathogenic organisms.
Cloned genes may confer pathogenic properties to nonpathogenic strain.
2. Random or targeted mutagenesis to look for loss of virulence.
To identify factors required for virulence, you need to be able to
measure a pathogen’s virulence:
For this reason, we rely upon animal models and cell culture models.
Salmonella: A model for
bacterial pathogenesis
Salmonella: A model for
bacterial pathogenesis.
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Upon reaching the small intestine, they are taken up by intestinal M cells by a process termed bacterial
mediated endocytosis.
They exist in vesicles, which migrate to the basolateral surface and are released into the bloodstream. It is
here they encounter macrophages, which engulf them.
Bacteria have their own mechanisms to survive and
proliferate inside macrophages and they are carried to other organs
of the body.
Can go from lumen, cross intestinal wall into blood stream and can
become a very serious infection
Invasion refers to the step where the salmonella cell is
internalizing itself into the epithelial cell
Cloning and molecular characterization of genes whose
products allow Salmonella typhimurium to penetrate tissue culture
cells
Grow epithelial cells attached to plastic dish for assay
for salmonella internalization PNAS 86;
6383-6387
Add bacteria
Incubate and allow bacteria to bind to cells
and/or internalize
Remove media and solubilize epithelial cells
with a detergent that does not hurt the bacteria
and determine total bacterial cells present
The strain that binds to cultured cell and may be
internalized is able to grow
The nonbinding strain does not
Alternatively, remove media and incubate cells
with antibiotic that kills salmonella but cannot
cross cell plasma membrane
Solubilize and determine the number
of bacteria present
The strain that can penetrate cells
(inv+) grows on assay
The strain that cannot penetrate cells
(inv-) does not
percent adherence is the same for the
first two strains, while percent invasion
is highly detected in the second strain;
the first strain can adhere but cannot
invade
transposons
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