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