Antibiotic Resistance I

Question 1

Plasmid

Answer 1

It is an autonomous, self-replicating, extrachromosomal element composed of circular or linear, double- stranded DNA.

Question 2

Conjugative (conjugal) plasmids

Answer 2

They can autonomously transfer themselves from one host to another; therefore, passing antibiotic resistance to other individuals within the species or to individuals in other species or even to individuals in other genera.

Question 3

Non-conjugative (non-conjugal) plasmids

Answer 3

They cannot transfer themselves. However, they can be transferred by a conjugative plasmid.

Question 4

Lytic (productive) infection

Answer 4

After infection, the viral genome replicates and causes the host cell to lyse, which permits progeny viruses to release into the environment.

Question 5

Lysogenic (latent or temperate) infection

Answer 5

After infection, the virus does not replicate, because all the genes necessary for the lytic infection become turned off (repressed). Thus, the lysogenic phage genome, called a prophage, becomes latent. Prophages can either circularize and remain autonomous like plasmids or integrate into and become part of the host chromosome.

Question 6

Transposable Elements

Answer 6

They are genetic units that mediate their own transfer from one location in a genome to another location within the same genome or from one genome to another in same cell

Question 7

Insertion Sequence (IS) Element

Answer 7

An IS element is a segment of DNA about 1000 bp in length that only carries genes for its own transposition. These genes include a site-specific recombinase (an enzyme that recombines DNA) and two distinct nucleotide recognition sequences located at each terminus in inverted order.

Question 8

What is the structure of an IS?

Answer 8

IR - Recombinase - IR

Question 9

Transposon

Answer 9

It consists of a central core of genes bounded by two IS elements. Because they contain two IS elements, they carry the genes necessary for transposition. The core genes can encode for a variety of functions, including resistance to antimicrobial agents, e.g. antibiotics.

Question 10

Conjugal transposon

Answer 10

In a conjugal transposon, the 2 IS elements flank genes that encode antibiotic resistance and conjugal machinery. Thus, these multiply resistant transposons jump from location to location within a given cell, but because they also carry the genes required for conjugation, they also mediate their own transfer to other cells

Question 11

R Plasmid

Answer 11

An R plasmid is a conjugal plasmid that also carries genes that confer resistance to antibiotics. Often, they carry several resistance genes; thus, a cell that carries such an R plasmid is resistant to multiple antibiotics.