Antimicrobial resistance Flashcards
How do you carry out a disk diffusion antimicrobial test
(7)
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
What are the two strains you would carry out disk diffusion for?
E. Coli or Staphylococci
What five disks are used for staphylococci
Cefoxitin 30ug
Ciproflaxacin 5 ug
Erythromycin 15ug
Gentamicin 10ug
Penicillin 1 ug
What five disks are used for E.Coli
Ampicillin
Cefotaxime
Ceftazidine
Gentamicin
Ertapenem
What three results can you have
Susceptible (S)
Susceptible-increased exposure (I)
Resistant (R)
What does susceptible mean
Standard dosing regimen - implies a high likelihood of therapeutic success using a standard dosing regimen of the agent
What does increased exposure mean
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
What does resistant mean
Implies there is a high likelihood of therapeutic failure even when there is increased exposure
What does MIC stand for
Minimum inhibitory concentration
What does MIC measure
It measures an organisms susceptibility against different concentrations of antibiotics
What is MIC carried out on?
E. Coli
How do you carry out an MIC
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
List the three classifications of B-lactams
Penicilins
Cephalosporin
Carbapenems
List the penicillins
Penicillin
Ampicillin
Augmentin
Methicillin
List the cephalosporins
Cefotaxime
Ceftazidime
Cefpodoxine
List the carbapenems
Meropenem
What is ESBL-mediated resistance
Extended spectrum beta-lactam mediated resistance
What group of organisms express ESBL-mediated resistance
Enterobacterales
Prevalent in Klebsiella pneumoniae and E.Coli
How does ESBL-mediated resistance work
Resistance arose due to the production of B-lactamase enzymes with the ability to hydrolyse broad spectrum B-lactams i.e. cefotaxime and ceftazidime
What test results would make you want to investigate ESBL-mediated resistance
Resistance to B-lactams such as cefotaxime and ceftazidime
How do you test for ESBL-mediated resistance?
(4)
MH agar
Lawn inoculum
Ceftaxidime and ceftazidime-plus-clavulanic acid discs are added
Measure zone diameters
What does clavulanic acid do?
(3)
Clavulanic acid inhibites ESBL-mediated resistance
It should make the organism now susceptible to the antibiotics
Used to ID ESBL
How do you read your clavulanic acid result
If the zone size of the combination disc is increased by 5mm compared to the zone size of the cephalosporin alone
What should you do if your bacteria is ESBL positive
Investigate CPE-mediated resistance
What are CPEs?
Carbapenemase producing enterobacterales (CPEs)
What are CPEs so dangerous?
Carbapenems were considered a last line treatment for multi-drug resistant bacterial infections
Up to 50% mortality rate with these infections
What are the five major groups of CPEs
The big five;
KPC- variant enzymes
IMP- variant enzymes
VIM- variant enzymes
NDM- variant enzymes
OXA - variant enzymes
What is notable about the KPCs
The Klebsiella pneumoniae carbapenemases are the most widespread mediating resistance to all B-lactam antibiotics
How do we detect CPEs?
Lateral-flow immunochromatography assays are used
The RESIST-5 O.O.K.N.V lateral flow assay
How does the RESIST-5 O.O.K.N.V lateral flow assay work
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
How do you use a RESIST-5 test
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
