HCAI 3 - Epidemiology

Question 1

Way to compare bacterial genomes

Answer 1

With Single Nucleotide Polymorphisms (SNPs)

Question 2

Phylogenetics

Answer 2

Inferring phylogeny from a set of taxa

Estimates evolutionary relationships between groups of taxa

Question 3

Enterococcus faecium

Answer 3

Normal commensal organism
Intrinsically resistant to cephalosporins and aminoglycosides
Acquired glycopeptide resistance

Question 4

Example of a glycopeptide antibiotic

Answer 4

Vancomycin

Question 5

Factor transforming VSE to VRE

Answer 5

Enterococci acquire a transposon with a vancomycin resistance loci on it

Question 6

Most common vancomycin-resistance loci in Australia

Answer 6

VanB

Question 7

Effect of VanB

Answer 7

Encodes for a ligase

Ligase modifies peptidoglycan wall so that vancomycin can’t bind - D-ala-D-ala to D-ala-D-lac

Question 8

Transposon with VanB locus

Answer 8

TN1549

Question 9

Size of TN1549

Answer 9

33kb

Question 10

E test

Answer 10

A strip of antibiotic-impregnated paper is placed on a bacterial colony.
Progressively lower concentration

Question 11

Model A of transmission

Answer 11

Patient enters hospital with VRE, spreads it to other patients
Counter with handwashing, screening patients as they enter hospital

Question 12

Alternative model of VanB transmission

Answer 12

VRE exist in gut as commensal flora
Transfer TN1549 to VSE
TN1549 is selected for when vancomycin is introduced into gut

Question 13

Situation where vancomycin resistance can arise de novo

Answer 13

Broad-spectrum antibiotics are used
Lateral gene transfer is selected for (TN1549)
TN1549 transferred from bowel anaerobes to colonising VSE

Question 14

Dominant lineage of E. faecium

Answer 14

ST203

Question 15

How can we tell how TN1549 has been acquired?

Answer 15

Use flanking sequences to see whether it has been inserted backwards or forwards

Question 16

Is the insertion of VanB into TN1549 random?

Answer 16

No. There are some sites where VanB is more common

Question 17

Number of VRE likely to have arisen by se novo evolution

Answer 17

18/36

Question 18

Ways to control spread of VRE

Answer 18

Test for both VRE and VSE

Control antibiotic use - A patient receiving antibiotics could become a source of VRE