L14 Dissemination of Antibiotic Resistance Genomes I Flashcards
All genomes are made of DNA, with the exception of ___.
RNA viruses
Genomes range in ___.
Size
What are the three major types of genomes?
- Chromosomal (bacterial)
- Plasmid (episome)
- Bacterial virus (phage)
What are some features of the chromosomal (bacterial) genome?
- Large (avg. 4000 genes)
- Tightly packed and folded into a nucleoid
- Typically haploid
- Circular or linear
What is the clinical relevance of the chromosomal genome?
Can encode for certain antibiotic resistance and virulence factors
Describe the process of packaging of DNA into a chromosomal genome.
- DNA
- 40-nm fiber
- 80-nm fiber
- 300-nm loop
- Supercoiled loop
- Tightly-packed (transcriptionally inactive)
When is the chromosomal genome inactive?
During the late stationary and lag phases
True or false - the plasmid genome is part of the bacterial chromosome.
False - it is part of the bacterial GENOME
What are some features of the plasmid (episomal) genome?
- Autonomous, self-replicating
- Extrachromosomal
- Double-stranded DNA
- Tend to be small
- Usually circular, can be linear
What is the clinical relevance of the plasmid genome?
Plasmids often carry genes that encode virulence factors (like pili or toxin) and proteins that confer antibiotic resistance
Which type of genome can be easily transferred from host to host?
Plasmid genome
What are the two types of plasmids?
- Conjugative
2. Non-conjugative
What is a conjugative plasmid?
A plasmid that can autonomously transfer themselves from one host to another (within or between species)
What is a non-conjugative plasmid?
A plasmid that cannot transfer themselves; however, they can be transferred by conjugative plasmids
What are some features of the bacterial virus (phage) genome?
- Made of RNA or DNA
- Double or single-stranded
- Linear or circular
- 3-300 kb
What is the clinical relevance of the phage genome?
Phage genomes can carry genes that encode virulence factors
What are two examples of virulence factors carried by phages?
- Beta-toxin of diptheria
2. Toxin of cholera
What is a lytic infection?
An infection by a phage in which the genome replicates itself, lyses the host cell, and releases the progeny phage.
What is a lysogenic infection?
An infection by a phage in which the phage becomes latent and does not replicate; the phage genome (prophage here) can circularize and remain autonomous or integrate into the host chromosome
What are transposable elements?
Genetic units that mediate their own transfer form one location in a genome to another location within the same genome or from one genome to another IN THE SAME CELL
Why are transposable elements clinically relevant?
They are the major carrier of antibiotic resistance genes (by finding their way to phage and conjugal plasmids)
What does transposition rely on?
The ability of transposable elements to synthesize their own specific recombination enzymes.
Transposons are built from ___ elements.
Insertion sequence
What is the smallest transposable element?
Insertion sequence elements
What is an insertion sequence comprised of?
Segments of DNA that only carry genes for transposition, including its own site-specific recombinase, and two distinct nucleotide recognition sequences located at each terminus in inverted order
Insertion into a gene causes a ___.
Mutation
What are the recombinase recognition sites?
Inverted repeats
What is the transposition enzyme?
Recombinase (transposase)
What are transposons?
Transposable elements containing genes necessary for transposition and other functions.
What are the four major types of transposable elements?
- Insertion sequence elements
- Transposons
- Transposable prophages
- Conjugal transposons
What is a transposon?
2 IS elements flanking a resistance gene
What is a transposable prophage?
A bacteriophage that is a transposon
What is a conjugal transposon?
A transposon that carries genes for gene transfer (conjugation)
Gene exchange systems can move transposons ___. What does this permit?
Between cells; permits transfer of resistance from cell-to-cell
A bacteriophage can alternate between lytic and lysogenic states. In which state can it transpose?
Lysogenic phase
Where are conjugal transposons found?
Streptococcal enterococcus facaelis and many bacteroides species
___ carry multiple antibiotic resistance genes.
R plasmids
R plasmids typically carry resistance genes that encode enzymes that do what 2 functions?
- Inactivate antibiotics
2. Reduce cell’s permeability to antibiotics
Resistances conferred by chromosomal mutation usually involve what process?
Modification of the antibiotic target
How can R plasmids acquire resistances?
- Fusion to other plasmids
2. Acquiring transposons
Many Gram ___ bacteria carry R plasmids that carry multiple resistances.
Negative
