Etest Reading 2
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Transcript of Etest Reading 2
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Etest Reading
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EtestReading
AB bioMrieux 2008
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Etest Reading
Endpoint criteria relates to: Technical issues
Drug specific
Organism specific
Resistance mechanisms
Consult technical documents
Etest Reading Guides (ERG 001, 002)
Customer Information Sheets (CIS 006, CIS 007)
Etest Technical Guide (ETG 006) Mycobacteria
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Small molecule, larger ellipse Large molecule, smaller ellipse
Molecule Size
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Basic Etest Reading
Read MIC where growth intersects the strip
If between markings, read upper MIC value
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Between Markings
Read the upper value
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First Reading Step Sharp Endpoints
Is it a sharp endpoint?
YES: then read MIC where
growth intersects the strip.VA, MIC 1.0 g/mL
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Second Reading Step Not a Sharp Endpoint
Is it a sharp endpoint? NO: Is the drug bacteriostatic or
bactericidal?
Rule:
CIDAL DRUGS: Read at completeinhibition of ALL GROWTH (haze,micro- and macrocolonies), Read 100%inhibition. MIC 0.064 g/mL
STATIC DRUGS: Read at the firstsignificant inhibition of growth. Ignoretrailing and microcolonies. Read the so-called 80% inhibition. MIC 0.032 g/mL
staticcidal
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Macrocolonies
Always readmacrocolonies forboth static and cidaldrugs.
MIC 256 g/mL
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Sharp or Hazy Endpoint?
MIC 1.5 g/mL
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Sharp or Hazy Endpoint?
MIC 32 g/mL
BactericidalREAD macrocolonies,microcolonies and
trailing
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Sharp or Hazy Endpoint?
MIC 0.032 g/mL
BacteriostaticIGNORE trailing and
microcolonies
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Sharp or Hazy Endpoint?
MIC 0.75 g/mL
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Sharp or Hazy Endpoint?
MIC 0.094 g/mL
Read microcoloniesbetween 0.064-0.094
Bactericidal
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Sharp or Hazy Endpoint?
MIC 0.25 g/mL
Read first significantinhibition of growth,80% rule
Bacteriostatic
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Avoid too heavy an inoculum
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Ignore tunnel of growth along strip
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If uneven intersection - read upper value if 1 dilution
If > 1 dilution, test must
be repeated
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Proteus - dont read the swarm!
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Dont read haemolysis
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Bactericidal Drugs
-lactams
Carbapenems
Cephalosporins
Ethambutol
Glycopeptides
Fosfomycin
Isoniazide
Aminoglycosides
Quinolones
Metronidazole
Rifampicin
Amphotericin B
Read at complete inhibition
Look for hazes, micro- and macrocolonies
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Pneumo - Pen G
Obtain good confluentgrowth
Look formicrocolonies andhazes
MIC: 4.0 g/mL
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Look for colonies in the dip
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Observe microcolonies from 8 to 32
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Paradoxical effect - beta-lactams
Induction of regrowth athigher concentrations of the
antimicrobial
Read the highest value
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Bacteriostatic Drugs
Tetracyclines
Streptogramins
Oxazolidinones
Macrolides
Azoles
Lincomycins
Chloramphenicol
Sulfonamides
Trimethoprim
Echinocandins
Read at 80% inhibition i.e. first point of significantchange as judged by the naked eye (CIS 007).
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80% for Bacteriostatic Drugs
Bacteriostatic drugs
Endpoint rule:
80% inhibition
MIC: 0.032 g/mL
Comment:
Read at the first point
of significant inhibitionas judged by the
naked eye
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Linezolid
Static endpoint at 90%
inhibition
MIC: 1 g/mL
Trailing: 0.5 2 g/mL
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MRSA - low level heteroresistance
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Other Reading Rules
Pipercillin/tazobactam
Ticarcillin/clavulanic acid
Ignore the inhibition of growthcaused by the activity of the inhibitor(tazobactam, clavulanic acid) andextrapolate the ellipse to give theMIC of pipercillin or ticarcillin.
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Echinocandins
Ignore regrowth athigher concentrations(paradoxical effect)
for echinocandins
MIC: 0.125 g/mL
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Distorted ellipse
Wet surface, repeat test
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Interpretation ofPOSITIVEEtest ESBL
Cephalosporin with Clavulanic acid shows 3 log dilution lower thancephalosporin without Clavulanic acid; ratio ofCT /CTL 8
Deformation of the ellipse
Phantom zone
All are Positive for ESBL
See Etest ESBL Package Insert
ESBL POSITIVE CT 0.5 and CT/CTL 8or
TZ 1 and TZ/TZL 8
or
PM 0.25 and PM/PML 8
or
Phantom zone or
deformation of the CT, TZor PM ellipse
Report:
ESBL producer and
resistant to all penicillins,
Cephalosporins
and aztreonam (CLSI
M100-S series).
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ESBL
MIC: CT 1.5 & CTL 0.047
CT/CTL 1.5/0.047= 32 = ESBL+
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ESBL +
Deformation of ellipse = ESBL +
Phantom zone = ESBL +
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Categorisation of S, I, R
Use MIC breakpoints from most recent CLSIM100-S or own regulatory body (eg. EUCAST,BSAC)
If not available, consult the litterature
Etest gives values in-between 2-fold dilutions
Round-up to next upper dilution before S, I, R
Report the exact MIC and S, I, R
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Interpreting 1/2 Dilution
S: 0.064
I: 0.125 - 1
R: 2
MIC 1.5 becomes 2 g/mL
Category = R
R
I
S
T h i l D t
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Technical Documents
Consult technical documents
Etest Reading Guides
ERG 001 antimicrobials ERG 002 - antifungals
Customer Information Sheets
CIS 006 list of static/cidal drugs
CIS 007 reading of sharp and hazy endpoints
Etest Technical Guide (ETG 006) Mycobacteria
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Etest Reading Practice
AB bioMrieux 2008
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FX code for:
Cefoxitin
Endpoint rule:
100% inhibition
MIC: 16 g/mL
Comment:
Dont over-read
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FX code for:
Cefoxitin
Endpoint rule:
100% inhibition
MIC: 32 g/mL
Comment:
Macro-colonies =resistant subpopulation
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CM code for:
Clindamycin
Endpoint rule:
80% inhibition
MIC: 256 g/mL
Comment:
Lawn of
macrocolonies indiscernable ellipse
means resistant
subpopulation
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MZ code for:
Metronidazole
Endpoint rule:
100% inhibition
MIC: 0.75 g/mL
Comment:
Wide ellipse, sharp
endpoint
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IP code for:
Imipenem
Endpoint rule:
100% inhibition
MIC: 0.064 g/mL
Comment:
Wide ellipse, slight
haze at endpoint
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AK code for:
Amikacin
Endpoint rule:
100% inhibition
MIC: 0.75 g/mL
Comment:
Sharp endpoint
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CH code for:
Clarithromycin
Endpoint rule:
80% inhibition
MIC: 1 g/mL
Comment:
Ignore hazes between
1-2
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TZ code for:
Ceftazidime
Endpoint rule:
100% inhibition
MIC: 32 g/mL
Comment:
Read allmicrocolonies (SCVs)
6 - 32
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VA code for:
Vancomycin
Endpoint rule:
100% inhibition
MIC: 1g/mL
Comment: Read all
growth
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EM code for:
Erythromycin
Endpoint rule:
80% inhibition
MIC: 0.064 g/mL
Comment:
Ignore hazes bet.
0.064- 0.19
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CO code for:
Colistin
Endpoint rule:
100% inhibition
MIC: 0.19 g/mL
Comment: Ellipse
tapers/ dips towards
the endpoint
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IP code for:
Imipenem
Endpoint rule:
100% inhibition
MIC: 8 g/mL
Comment:
Macrocolonies within
ellipse, ignore line of
growth along the strip
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OX code for:
Oxacillin
Endpoint rule:
100% inhibition
MIC: 32 g/mL
Comment:
Read all growth(colonies in ellipse =
mecA hetero-
resistance)
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LZ code for:
Linezolid
Endpoint rule:
90% inhibition
MIC: 1 g/mL
Comment: Ignore
hazes between 1-2
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CD code for:
Cefdinir (or other-lactam)
Endpoint rule:
100% inhibition
MIC: 256 g/mL
Comment:
Paradoxical effect, re-
growth 2- >256
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AT code for:Aztreonam
Endpoint rule:
100% inhibition
MIC: 3 g/mL
Comment: Sharp
endpoint
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MM code for:
Mecillinam
Endpoint rule:
100% inhibition
MIC: 256 g/mL
Comment:
Macrocolonies in ellipse
= resistantsubpopulation
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CE code for:
Cephalothin
Endpoint rule:
100% inhibition
MIC: 96 g/mL
Comment: Small
ellipse at high MIC
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TLc code for:
Ticarcillin/clavulanic acid (2 g/ mL)
Endpoint rule:
100% inhibition
MIC: 2 g/mL
Comment: Deformation of ellipse to
straight dip 4 0.023 due to
clav.acid activityExtrapolate ellipse curve to strip
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TLc code for:
Ticarcillin/clavulanicacid
Endpoint rule:
100% inhibition
MIC: 256 g/mL
Comment:
Resistance induced
by clavulanic acid
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DPC code for:
Daptomycin (overlaidwith constant level of
calcium)
Endpoint rule:
100% inhibition
MIC: 1.5 g/mL
Comment:Sharp endpoint
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FL code for:
Fluconazole
Endpoint rule:
80% inhibition
MIC: 0.19 g/mL
Comment:
Lawn of microcolonies indiscernable ellipse,
morphology change from
0.19
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FL code for:Fluconazole
Endpoint rule:
80% inhibition
MIC: 1 g/mL
Comment:
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IT code for:Itraconazole
Endpoint rule:
80% inhibition
MIC: 0.125 g/mL
Comment:Clear endpoint
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AP code for:
Amphotericin B
Endpoint rule:
100% inhibition
MIC: 0.38 g/mL
Comment:
Read all growthcarefully!
(microcolonies 0.125-
0.38)
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FC code for:
Flucytosine
Endpoint rule:
90% inhibition
MIC: 2 g/mL
Comment:
Ignore trailing, minute
colonies above 2
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FC code for:
Flucytosine
Endpoint rule:
90% inhibition
MIC: 0.094 g/mL
Comment:
Wide ellipse,ignore minute
colonies above
0.094
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CS code for:Caspofungin
Endpoint rule:
80% inhibition
MIC: 0.032 g/mL
Comment:
Sharp endpoint
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CS code for:
Caspofungin
Endpoint rule:
80% inhibition
MIC: 0.125 g/mL
Comment:
Sharp at 0.125, ignoreregrowth of
microcolonies 0.75 - 32