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46 Cards in this Set

  • Front
  • Back
Why do we care about gene transfer?
Because enterococcus has the ability to transfer Vancomycin resistance to MRSA.
Why do bacteria like to exchange genetic material?
-It increases their genetic diversity
-It gives them a selective advantage in certain environments
What is gene transfer predominantly responsible for?
The rapid spread of antibiotic resistance.
What are Plasmids?
Small ss or ds DNA molecules that replicate independently of the bacterial chromosome.
What shape are plasmids?
-Most often circular
-Can be linear
What are Transposons?
Smaller DNA segments that are capable of going from one spot to another and are NOT capable of replicating independently.
What is required for Transposons to be maintained?
They must be in association with either a plasmid or chromosome which has the machinery for replication.
What is a Pathogenicity Island?
A large region of DNA in the Chromosome that looks substantially different at the GC level than the rest of the genome itself.
What does the dissimilarity of Pathogenicity Islands imply?
That they were acquired from some other organism.
What are bacteriophages?
Virus-like molecules that infect only bacteria.
What are the 3 methods of gene transfer into bacteria?
1. Transformation
2. Transduction
3. Conjugation
What is transformation?
The simplest method of gene transfer; uptake of naked genetic material floating free in the environment.
What is conjugation?
Formation of a mating bridge and pore to allow for unidirectional genetic exchange from one microbe to another.
What is transduction?
Input of genetic material from a bacteriophage.
What is a bacterium that has LINEAR plasmids?
Borrelia burgdorferi
What is the most simple form of plasmid?
F plasmids - fertility
How many F plasmids can be found in a bacterium?
Only one
What are multiple copy plasmids?
Other plasmids that can be found in multiple copies in the cell.
Which is more likely to be causing drug resistance or virulence factor acquisition?
Multiple copy plasmids
By what methods can plasmids be transferred?
All three
What are Transposable elements?
Mobile DNA segments that can be transferred between different DNA molecules
What is at the end of Transposons?
Inverted terminal repeats
What enzyme do transposable elements have to contain the gene for?
What does Transposase do?
Recognize ITRs (inverted terminal repeats) on transposable elements
-nicks the DNA
-allows for transfer of the element
What are the 2 mechanisms by which transposition of transposable elements can occur?
1. Replicative transposition
2. Cut and paste transposition
What is the result of Replicative transposition?
1. Retain an original copy in its same spot
2. A new copy is made that goes somewhere else on the chromosome or plasmid
What is the result of cut and paste transposition?
-The original copy is simply moved, not in its same place.
What are the simplest and most common type of Transposable elements?
Insertion sequences - they have the bare minimum of what is required to be considered a transposable element.
What is tnp?
Transposase gene
So what does an insertion sequence look like?
What is a Composite transposon?
A gene region that has two insertion sequences flanking the ends of a central region that encodes an antibiotic resistance gene or a toxin gene.
What happens when you express the transposase gene from the insertion sequences on a composite transposon?
Transfer of any of the three possible elements - Left IS by itself, Right by itself, or the whole thing.
What enzyme is encoded by the more complicated TnA family?
Beta lactamase
What can transposons be carried by in addition to chromosomes and plasmids?
What are bacteriophage mediated transposons able to do that those carried on ch's or plasmids cannot?
They can be transferred from a host to a new host/microbe, instead of being retained by the same host.
What is the main difference between Plasmids and Transposable elements?
-Plasmids are INHERITED - from donor to recipient
-Transposons are cut and pasted and INTERFERE with gene function
What is a clinical example of a bacteria that use phase variation by inverting an insertion sequence?
The spontaneous switching between fimbriated and non-fimbriated forms of E. Coli
What can fimbriated E. coli do?
Attach to urinary tract epithelial cells and colonize the urinary tract.
Why would e. coli want to turn off its fimbriae once it has colonized the urinary tract?
To avoid antigenic stimulation of the immune system.
How were Genomic Pathogenicity islands identified?
By the sequencing of bacterial genomes.
How can you tell that genomic pathogenicity islands are not normal genes in a bacteria?
Their GC content differs from the majority of the chromosome
What is the tip off that pathogenicity islands were transferred onto a microbial genome by bacteriophage?
They are usually FLANKED by inverted repeats
What is encoded by the pathogenicity islands in Salmonella and Pseudomonas?
Type III secretion systems
What is encoded by the pathogenicity island in Clostridium botulinum?
What is encoded by the pathogenicity island in Vibrio cholerae?
Toxin co-regulated pilus (TCP)
What is encoded by the pathogenicity island in S. aureus?
Methicillin resistance genes