Lecture 25 - Molecular Epidemiology of HCAI Flashcards Preview

MIIM20002 - Microbes, Infections, Responses > Lecture 25 - Molecular Epidemiology of HCAI > Flashcards

Flashcards in Lecture 25 - Molecular Epidemiology of HCAI Deck (20)
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1
Q

What are we detecting when we do PFGE?

A

SNPs within the bacterial population

Create a phylogeny

Can determine relatedness and thus common source

2
Q

How do we differentiate bacterial in the population?

A

Sequencing

  • compare whole genomes
  • SNPs
3
Q

Describe E. faecium resistance

A

Intrinsic:

  • cephalosporins
  • aminoglycasides

Acquired:

  • glycopeptide antibiotics
  • VRE
4
Q

How does E. faecium get resistance to vancomycin?

A

Transposon Tn1549
with the VanB locus

Changes the peptidoglycan so that vancomycin can no longer bind

5
Q

Describe the transmission models of VRE

A

Model A:
- VRE spread from patient to patient in hospital

Alternative model:

  • people have gut anaerobe commensals with vanB locus, as well as VSE
  • in hospital, treatment with vancomycin selects for VRE
6
Q

What were the surprising findings about our gut commensal?

A

50% of gut commensals have vanB

7
Q

What was the French experiment with the mice?

A
  • Mice with gut commensals with vanB and VSE
  • Mice treated with vancomycin
  • Tn1549 transferred to VSE
  • VRE now selected for
8
Q

Is VSE commonly found in the gut microflora?

A

Yes

9
Q

Describe the process of genome sequencing

A
  1. Bacteria grown up
  2. DNA extracted
  3. Sequenced
  4. Analysed
10
Q

Describe the sequencing stage

A

Machines:

  • illumina
  • ion torrent

‘Reads’ read against reference genomes

11
Q

In the study, there were 61 …

A

invasive E. faecium isolated studied

12
Q

What is the phylogeny on slide 26?

A

Relatedness of the 61 isolates

  • core genomes of 61 were sequenced
  • many SNPs analysed
  • relatedness gave us the tree
13
Q

What is the phylogeny on slide 28?

What does it tell us?

A

Analysis of the sequence of the Tn1549
(resistance transposon)

  • two different types of the transposon
  • some other bacterial species have this transposon
14
Q

What are the different parameters to do with the transposon that can be analysed?

A
  • sequence of transposon
  • orientation of transposon
  • position of insertion
  • coupling sequence
15
Q

What would be observed when all the information about the transposon is overlayed on the core genome phylogeny if model A were correct?

Why?

A

Clonal spread

Closely related bacteria have similar transposon features

The transposon has been passed on from a common ancestor

16
Q

What would be observed when all the information about the transposon is overlayed on the core genome phylogeny if the alternative model were correct?

Why?

A

De Novo formation

Closely related bacteria have differe transposon features

Because the transposon has arisen de novo, not been passed on from common ancestors

17
Q

What conclusions have been made from this new study?

A

VRE arises by de novo evolution
(not clonal)

Gut anaerobes are potential sources of Tn1549

18
Q

What is the transposon that conferrs vancomycin resistance?

A

Tn1549

19
Q

What is vanB?

A

This is a single locus (gene) on the Tn1549 transposon

20
Q

What are the implications of the study for infection control?

A
  • patients being treated with vancomycin are potential sources of VRE
  • identification and isolation of patients with VSE also required
  • need antibiotic control policies
  • universal precautions still warranted