Lecture 12

Question 1

What is the consequence of plasmid multimers?

Answer 1

Bigger chance of plasmid loss during cell division

Question 2

How are plasmid multimers formed?

Answer 2

Recombination

Question 3

How are plasmid-free cells controlled?

Answer 3

Killed via post-segregational killing systems

Question 4

What is ColE1’s killing system?

Answer 4

Excretion of colicin

->cells without the immunity protein will die

Question 5

What is F’s killing system?

Answer 5

Has two systems

1. Hok Sok
2. ccdA, B : ccdB

Question 6

Describe the ccdA, B : ccdB system

Answer 6

B : ccdB is a stable killer protein
ccdA is an unstable blocking protein which breaks down quickly in the absence of plasmid which leaves the toxin to kill the cell

Question 7

Describe the Hok Sok System

Answer 7

1. Hok (host killing)
   - smaller killer peptide (membrane depolarisation)
   - Hok translated from stable messenger RNA (half-life of 20 minutes
2. Sok (suppressor of host-killing)
   - unstable antisense RNA (half life of 5 minutes)
   - binds to Hok mRNA and prevents translation

Question 8

What is the effect of NDM-1?

Answer 8

Bacteria with this are resistant to almost all antibiotics

Question 9

What was found when an isolated strain of E.coli containing NDM-1 was compared to another strain?

Answer 9

It had a 97% identical backbone to a broad-host-range plasmid that was found in Lebanon. This part of the plasmid gave UV resistance

The remaining area gave the more severe resistance characteristics
->Beta-lactams being particularly dangerous