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2.2 Microbiology > Antimicrobial resistance > Flashcards

Antimicrobial resistance Flashcards

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1
Q

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

A

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

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2
Q

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

A

E. Coli or Staphylococci

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3
Q

What five disks are used for staphylococci

A

Cefoxitin 30ug

Ciproflaxacin 5 ug

Erythromycin 15ug

Gentamicin 10ug

Penicillin 1 ug

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4
Q

What five disks are used for E.Coli

A

Ampicillin
Cefotaxime
Ceftazidine
Gentamicin
Ertapenem

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5
Q

What three results can you have

A

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

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6
Q

What does susceptible mean

A

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

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7
Q

What does increased exposure mean

A

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

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8
Q

What does resistant mean

A

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

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9
Q

What does MIC stand for

A

Minimum inhibitory concentration

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10
Q

What does MIC measure

A

It measures an organisms susceptibility against different concentrations of antibiotics

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11
Q

What is MIC carried out on?

A

E. Coli

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12
Q

How do you carry out an MIC

A

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

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13
Q

List the three classifications of B-lactams

A

Penicilins

Cephalosporin

Carbapenems

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14
Q

List the penicillins

A

Penicillin
Ampicillin
Augmentin
Methicillin

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15
Q

List the cephalosporins

A

Cefotaxime
Ceftazidime
Cefpodoxine

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16
Q

List the carbapenems

A

Meropenem

17
Q

What is ESBL-mediated resistance

A

Extended spectrum beta-lactam mediated resistance

18
Q

What group of organisms express ESBL-mediated resistance

A

Enterobacterales

Prevalent in Klebsiella pneumoniae and E.Coli

19
Q

How does ESBL-mediated resistance work

A

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

20
Q

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

A

Resistance to B-lactams such as cefotaxime and ceftazidime

21
Q

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

A

MH agar

Lawn inoculum

Ceftaxidime and ceftazidime-plus-clavulanic acid discs are added

Measure zone diameters

22
Q

What does clavulanic acid do?
(3)

A

Clavulanic acid inhibites ESBL-mediated resistance

It should make the organism now susceptible to the antibiotics

Used to ID ESBL

23
Q

How do you read your clavulanic acid result

A

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

24
Q

What should you do if your bacteria is ESBL positive

A

Investigate CPE-mediated resistance

25
Q

What are CPEs?

A

Carbapenemase producing enterobacterales (CPEs)

26
Q

What are CPEs so dangerous?

A

Carbapenems were considered a last line treatment for multi-drug resistant bacterial infections

Up to 50% mortality rate with these infections

27
Q

What are the five major groups of CPEs

A

The big five;

KPC- variant enzymes

IMP- variant enzymes

VIM- variant enzymes

NDM- variant enzymes

OXA - variant enzymes

28
Q

What is notable about the KPCs

A

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

29
Q

How do we detect CPEs?

A

Lateral-flow immunochromatography assays are used

The RESIST-5 O.O.K.N.V lateral flow assay

30
Q

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

A

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

31
Q

How do you use a RESIST-5 test

A

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

2.2 Microbiology (60 decks)

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