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):
1

What are we detecting when we do PFGE?

SNPs within the bacterial population

Create a phylogeny

Can determine relatedness and thus common source

2

How do we differentiate bacterial in the population?

Sequencing
- compare whole genomes
- SNPs

3

Describe E. faecium resistance

Intrinsic:
- cephalosporins
- aminoglycasides

Acquired:
- glycopeptide antibiotics
- VRE

4

How does E. faecium get resistance to vancomycin?

Transposon Tn1549
with the VanB locus

Changes the peptidoglycan so that vancomycin can no longer bind

5

Describe the transmission models of VRE

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

What were the surprising findings about our gut commensal?

50% of gut commensals have vanB

7

What was the French experiment with the mice?

- Mice with gut commensals with vanB and VSE
- Mice treated with vancomycin
- Tn1549 transferred to VSE
- VRE now selected for

8

Is VSE commonly found in the gut microflora?

Yes

9

Describe the process of genome sequencing

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

10

Describe the sequencing stage

Machines:
- illumina
- ion torrent

'Reads' read against reference genomes

11

In the study, there were 61 ...

invasive E. faecium isolated studied

12

What is the phylogeny on slide 26?

Relatedness of the 61 isolates

- core genomes of 61 were sequenced
- many SNPs analysed
- relatedness gave us the tree

13

What is the phylogeny on slide 28?

What does it tell us?

Analysis of the sequence of the Tn1549
(resistance transposon)

- two different types of the transposon
- some other bacterial species have this transposon

14

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

- sequence of transposon
- orientation of transposon
- position of insertion
- coupling sequence

15

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

Why?

Clonal spread

Closely related bacteria have similar transposon features

The transposon has been passed on from a common ancestor

16

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?

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

What conclusions have been made from this new study?

VRE arises by de novo evolution
(not clonal)

Gut anaerobes are potential sources of Tn1549

18

What is the transposon that conferrs vancomycin resistance?

Tn1549

19

What is vanB?

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

20

What are the implications of the study for infection control?

- 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