Lecture 14 - Integrons and R plasmids Flashcards
What is the clinical progression of resistance/
- MSSA mild skin infection = beta-lactams
- Beta lactam purifies MRSA
- Vancomycin = resistant enterococcus
What are the 3 modes of antibiotic action?
- CW synthesis inhibition
- protein synthesis inhibition
- DNA rep/repair inhibition
Define multiple drug resistance
Resist multiple classes of antimicrobials
Use an example to describe inactivation by degradation - resistance, MGE, antibiotic eg
- beta-lactamases/penicillinases convert ring to penicilloic acid
- R plasmids, transposons
- extended spectrum ESBLs
- macrolides eg erythromycin EreB esterase degrading erythromycin ring
Use 3 examples to describe inactivation by modification - resistance, MGE, antibiotic eg
- modify active site
- aminoglycosides (-mycins) targeting 16S = phosphotranferase, adenyltransferase, acetyltransferase
- Chloramphenicol targeting 23S = chloramphenicol acetyltransferase
- Macrolides = macrolide phosphotransferase
- R plasmids esp pMS97, transposons
How do efflux pumps contribute to resistance and how are they encoded?
- mutated transport pumps using ATP/PMF to decrease conc
- Intrinsic resistance from chromosome encoded pumps, plasmid encoded
Explain vancomycin resistance by target replacement/modification
- Vancomycin binds terminal D-alas with high affinity to prevent crosslinking
- N-acyl-D-ala or N-acyl-D-ala-D-lac = low affinity
- Integron = Van genes to convert D-ala
What are the 4 integron-encoded Van genes for vancomycin resistance?
- VanH dehydrogenase = lactate
- VanX D, D-carboxypeptidase = remove terminal D-ala
- VanY D, D-dipeptidase = hydrolyses D-ala-D-ala
- VanA ligase = ester bond between D-ala and D-lac
Explain macrolide and beta-lactam resistance by target replacement/modification
- Macrolides = ribosomal protection protein blocking binding on R plasmids, transposons, integrons, eg TetM
- Methicillin resistance = low affinity PBP on R plasmids, transposons, integrons, eg S aureus MecA
How are R plasmids spread and what is their general structure incl the specific plasmid as the basic building block
- conjugation or vertical transfer
- conjugation or compound transposon with resistance marker
- IncW conjugative plasmid building block
Explain how mobilisible transposons are related/co-exist with R plasmids for resistance
- mobilise transposon by mob region on plasmid with relaxosome genes (plasmid transfer)
- Co-existing transposon and plasmid by opposite Inc groups
- both mobilisible plasmid and R plasmid nicked during conjugation
What are integrons and their key enzyme?
- modified transposons which capture and integrate then move with plasmid/transposon
- Integrase = phage enzyme to capture genes, flexible size = flexible no. of genes, 70 resistance cassettes
What is the structure of an integron
- Integrase int1 with recombo attL site
- variable cargo
- 3 open reading frames downstream of promoter = sulfonamide resistance, free circular gene cassette with recombo attC site and no ori
Describe the 4 step process of gene movement into an integron
- Integrase = recombo @ attL and attC = insert cassette downstream of P
- Transcribe gene 1 = feature phenotype
- Integrase = recombo @ attL and attC sites = excision or rearrangement
- Repeat
What are the 2 key features of genes in integrons that are unique to integrons
- no ori within genes = must be in integron for expression via P
- retain attC and attL sites for reshuffling
Where do integrons come from and why are they a resistance concen?
Unknown origin but widespread and coevolving with R plasmids to increase resistance
How do mutations contribute to resistance? Explain using an example
-Mutation of target site = less binding
- Eg. Methionine mutated in DNA gyrase B subunit = same function but less binding of novobiocin antibiotic
