L14 Dissemination of Antibiotic Resistance Genomes I

Question 1

All genomes are made of DNA, with the exception of ___.

Answer 1

RNA viruses

Question 2

Genomes range in ___.

Answer 2

Size

Question 3

What are the three major types of genomes?

Answer 3

1. Chromosomal (bacterial)
2. Plasmid (episome)
3. Bacterial virus (phage)

Question 4

What are some features of the chromosomal (bacterial) genome?

Answer 4

1. Large (avg. 4000 genes)
2. Tightly packed and folded into a nucleoid
3. Typically haploid
4. Circular or linear

Question 5

What is the clinical relevance of the chromosomal genome?

Answer 5

Can encode for certain antibiotic resistance and virulence factors

Question 6

Describe the process of packaging of DNA into a chromosomal genome.

Answer 6

1. DNA
2. 40-nm fiber
3. 80-nm fiber
4. 300-nm loop
5. Supercoiled loop
6. Tightly-packed (transcriptionally inactive)

Question 7

When is the chromosomal genome inactive?

Answer 7

During the late stationary and lag phases

Question 8

True or false - the plasmid genome is part of the bacterial chromosome.

Answer 8

False - it is part of the bacterial GENOME

Question 9

What are some features of the plasmid (episomal) genome?

Answer 9

1. Autonomous, self-replicating
2. Extrachromosomal
3. Double-stranded DNA
4. Tend to be small
5. Usually circular, can be linear

Question 10

What is the clinical relevance of the plasmid genome?

Answer 10

Plasmids often carry genes that encode virulence factors (like pili or toxin) and proteins that confer antibiotic resistance

Question 11

Which type of genome can be easily transferred from host to host?

Answer 11

Plasmid genome

Question 12

What are the two types of plasmids?

Answer 12

1. Conjugative

2. Non-conjugative

Question 13

What is a conjugative plasmid?

Answer 13

A plasmid that can autonomously transfer themselves from one host to another (within or between species)

Question 14

What is a non-conjugative plasmid?

Answer 14

A plasmid that cannot transfer themselves; however, they can be transferred by conjugative plasmids

Question 15

What are some features of the bacterial virus (phage) genome?

Answer 15

1. Made of RNA or DNA
2. Double or single-stranded
3. Linear or circular
4. 3-300 kb

Question 16

What is the clinical relevance of the phage genome?

Answer 16

Phage genomes can carry genes that encode virulence factors

Question 17

What are two examples of virulence factors carried by phages?

Answer 17

1. Beta-toxin of diptheria

2. Toxin of cholera

Question 18

What is a lytic infection?

Answer 18

An infection by a phage in which the genome replicates itself, lyses the host cell, and releases the progeny phage.

Question 19

What is a lysogenic infection?

Answer 19

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

Question 20

What are transposable elements?

Answer 20

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

Question 21

Why are transposable elements clinically relevant?

Answer 21

They are the major carrier of antibiotic resistance genes (by finding their way to phage and conjugal plasmids)

Question 22

What does transposition rely on?

Answer 22

The ability of transposable elements to synthesize their own specific recombination enzymes.

Question 23

Transposons are built from ___ elements.

Answer 23

Insertion sequence

Question 24

What is the smallest transposable element?

Answer 24

Insertion sequence elements

Question 25

What is an insertion sequence comprised of?

Answer 25

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

Question 26

Insertion into a gene causes a ___.

Answer 26

Mutation

Question 27

What are the recombinase recognition sites?

Answer 27

Inverted repeats

Question 28

What is the transposition enzyme?

Answer 28

Recombinase (transposase)

Question 29

What are transposons?

Answer 29

Transposable elements containing genes necessary for transposition and other functions.

Question 30

What are the four major types of transposable elements?

Answer 30

1. Insertion sequence elements
2. Transposons
3. Transposable prophages
4. Conjugal transposons

Question 31

What is a transposon?

Answer 31

2 IS elements flanking a resistance gene

Question 32

What is a transposable prophage?

Answer 32

A bacteriophage that is a transposon

Question 33

What is a conjugal transposon?

Answer 33

A transposon that carries genes for gene transfer (conjugation)

Question 34

Gene exchange systems can move transposons ___. What does this permit?

Answer 34

Between cells; permits transfer of resistance from cell-to-cell

Question 35

A bacteriophage can alternate between lytic and lysogenic states. In which state can it transpose?

Answer 35

Lysogenic phase

Question 36

Where are conjugal transposons found?

Answer 36

Streptococcal enterococcus facaelis and many bacteroides species

Question 37

___ carry multiple antibiotic resistance genes.

Answer 37

R plasmids

Question 38

R plasmids typically carry resistance genes that encode enzymes that do what 2 functions?

Answer 38

1. Inactivate antibiotics

2. Reduce cell’s permeability to antibiotics

Question 39

Resistances conferred by chromosomal mutation usually involve what process?

Answer 39

Modification of the antibiotic target

Question 40

How can R plasmids acquire resistances?

Answer 40

1. Fusion to other plasmids

2. Acquiring transposons

Question 41

Many Gram ___ bacteria carry R plasmids that carry multiple resistances.

Answer 41

Negative