R Plasmids

Question 1

R Plasmids Basics 101

Answer 1

• generated from the transposition of a transposon into a conjugal plasmid
• carry MULTIPLE ab resistance genes
• genes responsible for resistance usually code for enzymes that INACTIVATE AB OR REDUCE cell’s permeability to AB
• vs. resistances conferred by chromosomal mutation usually invlving the modifcation of the AB targe, eg RNAP and streptomycin
• evolve quickly, easily acquire resistance by fusing to other plasmids via IS element sor by acquiring new transposons
• amplify themselves by duplication OR by increasing the number of plasmids
• many NONPATHOGENIC bacteria carry R plasmids, serve as R plasmid RESERVOIRS for neighbors

Question 2

R Plasmids 1-Structure and Function

Answer 2

• because its a conjugal transposon it can mediate its OWN transfer from one host to another
• R plasmid vs. conjugal transposon:
  
  • R plasmid is an independent replicon (can replicate itself)
  • conjugal transposon is a molecular parasite, to replicate it must integrate into an existing replicon-most often a chromosome

Question 3

R Plasmids 2-Trouble, trouble, trouble

Answer 3

if it acquires the ability to mediate its OWN TRANSFER from one cell to another through CONJUGATION

Question 4

R Plasmids 3-RTF

Answer 4

RTF=resistance transfer factor.
RTF from Gram NEG bacteria can be passed ACROSS SPECIES
-selective pressure for one AB resistance by the presence of 1 AB can cause selection for MULTIPLE AB resistances

Question 5

R Plasmids 4-Build-a-Sto

Answer 5

• multiple resistance cassette-all of the AB in ONE REGION=less costly to the cell.
• If they were in separate locations would have to delete one to conserve energy and then it wouldn’t be there when you needed it