Antimicrobial resistance

Question 1

How do you carry out a disk diffusion antimicrobial test
(7)

Answer 1

Ask forMueller-Hinton agar

Create inoculum using a 0.5 McFarland turbidity standard

Inoculate plate, rotate 60 dergees 3 times

Place appropriate disks on plate

Press down gently with sterile forceps

Incubate at 37 degrees

Measure zone of inhibition

Question 2

What are the two strains you would carry out disk diffusion for?

Answer 2

E. Coli or Staphylococci

Question 3

What five disks are used for staphylococci

Answer 3

Cefoxitin 30ug

Ciproflaxacin 5 ug

Erythromycin 15ug

Gentamicin 10ug

Penicillin 1 ug

Question 4

What five disks are used for E.Coli

Answer 4

Ampicillin
Cefotaxime
Ceftazidine
Gentamicin
Ertapenem

Question 5

What three results can you have

Answer 5

Susceptible (S)
Susceptible-increased exposure (I)
Resistant (R)

Question 6

What does susceptible mean

Answer 6

Standard dosing regimen - implies a high likelihood of therapeutic success using a standard dosing regimen of the agent

Question 7

What does increased exposure mean

Answer 7

Implies a high likelihood of therapeutic success because exposure to the agent is increased by adjusting the dosing regimen or by its concentration at the site of infection

Question 8

What does resistant mean

Answer 8

Implies there is a high likelihood of therapeutic failure even when there is increased exposure

Question 9

What does MIC stand for

Answer 9

Minimum inhibitory concentration

Question 10

What does MIC measure

Answer 10

It measures an organisms susceptibility against different concentrations of antibiotics

Question 11

What is MIC carried out on?

Answer 11

E. Coli

Question 12

How do you carry out an MIC

Answer 12

Apply lawn inoculum of 0.5 McFarland standard to MH agar

Lawn inoculum, turn 60 degrees three times

Place E test in centre of plate

Incubate and check for growth

Question 13

List the three classifications of B-lactams

Answer 13

Penicilins

Cephalosporin

Carbapenems

Question 14

List the penicillins

Answer 14

Penicillin
Ampicillin
Augmentin
Methicillin

Question 15

List the cephalosporins

Answer 15

Cefotaxime
Ceftazidime
Cefpodoxine

Question 16

List the carbapenems

Answer 16

Meropenem

Question 17

What is ESBL-mediated resistance

Answer 17

Extended spectrum beta-lactam mediated resistance

Question 18

What group of organisms express ESBL-mediated resistance

Answer 18

Enterobacterales

Prevalent in Klebsiella pneumoniae and E.Coli

Question 19

How does ESBL-mediated resistance work

Answer 19

Resistance arose due to the production of B-lactamase enzymes with the ability to hydrolyse broad spectrum B-lactams i.e. cefotaxime and ceftazidime

Question 20

What test results would make you want to investigate ESBL-mediated resistance

Answer 20

Resistance to B-lactams such as cefotaxime and ceftazidime

Question 21

How do you test for ESBL-mediated resistance?
(4)

Answer 21

MH agar

Lawn inoculum

Ceftaxidime and ceftazidime-plus-clavulanic acid discs are added

Measure zone diameters

Question 22

What does clavulanic acid do?
(3)

Answer 22

Clavulanic acid inhibites ESBL-mediated resistance

It should make the organism now susceptible to the antibiotics

Used to ID ESBL

Question 23

How do you read your clavulanic acid result

Answer 23

If the zone size of the combination disc is increased by 5mm compared to the zone size of the cephalosporin alone

Question 24

What should you do if your bacteria is ESBL positive

Answer 24

Investigate CPE-mediated resistance

Question 25

What are CPEs?

Answer 25

Carbapenemase producing enterobacterales (CPEs)

Question 26

What are CPEs so dangerous?

Answer 26

Carbapenems were considered a last line treatment for multi-drug resistant bacterial infections Up to 50% mortality rate with these infections

Question 27

What are the five major groups of CPEs

Answer 27

The big five; KPC- variant enzymes IMP- variant enzymes VIM- variant enzymes NDM- variant enzymes OXA - variant enzymes

Question 28

What is notable about the KPCs

Answer 28

The Klebsiella pneumoniae carbapenemases are the most widespread mediating resistance to all B-lactam antibiotics

Question 29

How do we detect CPEs?

Answer 29

Lateral-flow immunochromatography assays are used The RESIST-5 O.O.K.N.V lateral flow assay

Question 30

How does the RESIST-5 O.O.K.N.V lateral flow assay work

Answer 30

This assays incorporates monoclonal anti-carbapenemase antibodies which act as specific capture probes for the direct detection of KPC, OXA-like, NDM and VIM CPEs

Question 31

How do you use a RESIST-5 test

Answer 31

Add 12 drops of LY-A buffer in the tube provided Re-suspend one test colony in the buffer Stir thoroughly and insert the dropper tightly Vortex until suspension is fully homogenised Invert the test tube and slowly add 3 drops of suspension into the sample well of the cassettes Allow to react for 15 mins max and read the result