etest reading 2

7/29/2019 Etest Reading 2

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Etest Reading


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EtestReading

AB bioMrieux 2008


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2

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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MIC 32 g/mL

BactericidalREAD macrocolonies,microcolonies and

trailing


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MIC 0.032 g/mL

BacteriostaticIGNORE trailing and

microcolonies


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MIC 0.75 g/mL


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MIC 0.094 g/mL

Read microcoloniesbetween 0.064-0.094

Bactericidal


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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