Antibiotic Resistance: Genomes

Question 1

Describe the bacterial chromosomal structure.

Answer 1

• nucleoid = bacterial genome; no membrane unlike euk
• has one or more haploid chromosomes
• histone-like organizational structure
• dsDNA
• circular or linear

Question 2

Describe the plasmid (episome) genome structure and function.

Answer 2

• circular/linear
• dsDNA
• autonomous replication
• extrachromosomal
• found in most bacteria; a cell can have 1 or many
• often carry virulence factors and antibiotic resistance

Question 3

Define transposable elements.

Answer 3

• jumping genes
• can transfer to different parts of the same genome OR from one genome to another
  => ex: bacterial genome to conjugal plasmid
• major carriers of antibiotic resistance
• do NOT transfer from one cell’s DNA to another cell’s DNA independently

Question 4

Explain why R plasmids represent the major reason for proliferation of multiple antibiotic resistance.

Answer 4

• transposon genes (several resistance genes) + conjugal plasmid
• can mediate transfer from one host to another
• independent replicon (unlike conjugal transposon)
• evolve quickly by fusing with other IS elements between cells
• can be found in pathogens (multiple resistance)
• can be found in non-pathogens acting as R plasmid reservoirs => conjugate into pathogenic cells nearby and confer resistance

Question 5

Define insertion sequence.

Answer 5

• simplest transposable element
• contains genes for recombinase enzyme and flanking inverted repeats recognition signal
• transposition of an IS into a gene will disrupt that gene’s function
• after transcription/translation => recombinase enzyme returns to the recognition sequences and transposes the IS into a target area
• IS transposition can be replicative (copy and paste) or non-replicative (cut and paste)
• building blocks for all other transposable elements

Question 6

Define conjugal transposon.

Answer 6

• 2 IS elements flank genes for ABX resistance and conjugal transference machinery
• genes can jump but also conjugate to other cells
• found in bacteria
• molecular parasite (cannot replicate on its own - must integrate into host genome)

Question 7

Define transposable prophage.

Answer 7

• 2 IS elements flank a bacteriophage
• phage genes permit lysogenic phage infection
• allows phage to insert anywhere in the host chromosome
• later undergoes lytic process, resulting in a new infection

Question 8

Define prophage

Answer 8

lysogenic phage genome

• can be a plasmid
• or integrate into host chromosome

Question 9

Define conjugal plasmids. Define non-conjugal plasmids.

Answer 9

CONJUGAL/CONJUGATIVE

• F and R
• autonomously transferred between hosts

NONCONJUGAL/NON-CONJUGATIVE

• cannot transfer themselves
• transferred by a conjugal plasmid
• used in genetic engineering

Question 10

Describe the bacteriophage genome structure and function.

Answer 10

• ss or ds
• RNA or DNA
• linear/circular
• encode virulence factors

Question 11

Differentiate between a lytic and lysogenic bacteriophage infection.

Answer 11

LYTIC (productive)

• viral genome replicates and causes host cell lysis
• progeny viruses are released

LYSOGENIC (latent, temperative)

• genes necessary for lytic infection are turned off/repressed
• virus does not replicate
• prophage becomes latent
• can circularize and become a plasmid OR insert into host chromosome

Question 12

Define transposon.

Answer 12

• hybrid
• consists of core genes flanked by IS elements
• carry genes for transposition because they have the IS elements
• core genes typically encode virulence and antibiotic resistance