Susceptibility Testing Systems

CLSI versus EUCAST

The ISO Reference Standard

Desirable Features of a Susceptibility Testing System

• Methods – Reliability

• Reproducibility, intra- and inter-laboratory

• Accuracy

• Precision

• International reference standard – To which it has been calibrated

• High predictive value – patient outcome – Driven by breakpoint selection

Broth or Disc Method?

• Broth methods – Basis of semi-automated systems which are

calibrated to ISO standard

– More readily comparable to the reference method

– Can generate MIC values (if on scale) which can be directly plugged into PK-PD parameters

• Disk methods – Much more flexible

– Requires good correlation with MIC breakpoints.

So what choices are there?

System Calibrated to

ISO reference

Breakpoint Setting

CLSI: Clinical and Laboratory Standards

Institute [www.clsi.org] Yes

Micro + PK/PD + Clinical

Outcome

EUCAST: European Committee on AST

[www.eucast.org] Yes

Micro + PK/PD + Clinical

Outcome

BSAC: British Society for Antimicrobial

Chemotherapy [bsac.org.uk/susceptibility] No Micro + PK/PD

CDS: Calibrated Dichomotous System

[web.med.unsw.edu.au/cdstest/] No Wild-type cutoffs

So what choices are there?

System Calibrated to

ISO reference

Breakpoint Setting

CLSI: Clinical and Laboratory Standards

Institute [www.clsi.org] Yes

Micro + PK/PD + Clinical

Outcome

EUCAST: European Committee on AST

[www.eucast.org] Yes

Micro + PK/PD + Clinical

Outcome

BSAC: British Society for Antimicrobial

Chemotherapy [bsac.org.uk/susceptibility] No Micro + PK/PD

CDS: Calibrated Dichomotous System

[web.med.unsw.edu.au/cdstest/] No Wild-type cutoffs

Most media the same except… Species/Group EUCAST CLSI

Streptococcus spp. Mueller-Hinton F MH + 5% sheep (disk)

MH + 2.5-5% LH (BMD) = ISO

Haemophilus influenzae(+para) Mueller-Hinton F Haemophilus Test Medium

Listeria monocytogenes Mueller-Hinton F MH + 2.5-5% LH (BMD) = ISO

M. catarrhalis Mueller-Hinton F MHB and MHA

Pasteurella multocida (spp.) Mueller-Hinton F MH + 5% sheep (disk)

MH + 2.5-5% LH (BMD) = ISO

Campylobacter jejuni/coli Mueller-Hinton F MH + 5% sheep (disk)

MH + 2.5-5% LH (BMD) = ISO

Most media the same except… Species/Group EUCAST CLSI

Corynebacterium spp. Mueller-Hinton F MH + 2.5-5% LH (BMD) = ISO

N. gonorrhoeae (MIC method) GC Agar + suppl.

N. meningitidis (MIC method) MH + 5% sheep (disk)

MH + 2.5-5% LH (BMD) = ISO

Helicobacter pylori (MIC method) MH + 5% sheep aged (disk)

Anaerobes (MIC method) Brucella + haemin + Vit K

(agar dilution, add LHB for BMD)

Difference in tests available for…

Species EUCAST v5 CLSI M100-S25 CLSI M45-A2

Pseudomonas spp.

Other Non-Enterobacteriaceae

S. maltophilia only 1 agent

H. parainfluenzae ()

N. gonorrhoeae disk

N. meningitidis disk

Gram-positive anaerobes

Gram-negative anaerobes

C. difficile specific

M. catarrhalis

Difference in tests available for…

Species EUCAST v5 CLSI M100-S25 CLSI M45-A2

H. pylori MIC

L. monocytogenes

P. multocida

C. jejuni and coli

Corynebacterium spp.

Abiotrophia spp., Granulicatella spp., Aeromonas spp., P. shigelloides, Bacillus spp., E. rhusiopathiae, HACEK group, Lactobacillus spp., Leuconostoc spp., Pediococcus spp., Vibrio spp., B. anthracis, Y. pestis, B. pseudomallei, B. mallei, F. tularensis, Brucella spp.

Difference in tests available for…

Species EUCAST v5 CLSI M100-S25

Cefazolin No

Cefoperazone-sulbactam No No

Cephalexin ( CZL - UTI)

Fosfomycin IV No

Fusidic acid Maybe soon?

Teicoplanin

Telavancin January 2016

Tigecycline FDA only

Tetracyclines unrevised

Older (uncommon) cephalosporins ( unrevised)

Older (uncommon) fluoroquinolones ( unrevised)

Older (uncommon) aminoglycosides ( unrevised)

Difference in Use of “Intermediate”

• CLSI uses “I” liberally, EUCAST sparingly – Buffer zone to prevent “S” “R“ (main reason) – Implies “S” where drug is concentrated

• EUCAST applies when only dose escalation is possible and widely used

• Questions that have vexed many over the years include – Should it be reported as such? – What will the clinician do with it? – Are our tests reproducible enough to rarely require its

use?

Differences in Disk Strengths Agent Species CLSI EUCAST

Ampicillin Enterococcus spp. H. influenzae P. multocida

10µg 2µg

Amoxycillin-clavulanate

H. influenzae M. catarrhalis P. multocida

20-10µg 2-1µg

Piperacillin Enterobacteriaceae Pseudomonas spp.

100µg 30µg

Piperacillin-tazobactam

Enterobacteriaceae Pseudomonas spp.

100-10µg 30-6µg

Cefotaxime Enterobacteriaceae Viridans Streptococcus spp. H. influenzae

30µg 5µg

Ceftazidime Enterobacteriaceae Pseudomonas spp.

30µg 10µg

Differences in Disk Strengths Agent Species CLSI EUCAST

Ceftaroline Enterobacteriaceae S. aureus

30µg 5µg

Netilmicin Enterobacteriaceae Staphylococcus spp.

30µg 10µg

Benzylpenicillin Staphylococcus spp. β-haem & viridans Streptococcus spp.

10 units 1 unit

Linezolid Staphylococcus spp. Enterococcus spp. β-haem Streptococcus spp.

30µg 10µg

Nitrofurantoin Enterobacteriaceae Staphylococcus spp. Enterococcus spp.

300µg 100µg

Vancomycin Enterococcus spp. β-haem Streptococcus spp. S. pneumoniae

30µg 5µg

Documentation

Feature EUCAST CLSI

METHODS

Disk diffusion V3: Manual, Slides, Reading Guide M2-A11

Dilution Refer ISO 20776-1 and website M7-A9

MEDIA PREPARATION Media prep document (V4) M2-A11 and M7-A9

QUALITY CONTROL TABLES QC Tables (V5.0) M100-S24

SOPs 7 documents M23-A3

ADDITIONAL TESTS Resistance Detection (V1) M100-S24

EXPERT RULES Expert Rules (V2) M100-S24

RATIONALE DOCUMENTS 39 documents 3 documents

GUIDANCE DOCUMENTS 5 documents M100-S24

FOREIGN LANGUAGES 8 languages By local arrangement

WILD-TYPE DISTRIBUTIONS MICs and Zone diameters None

Breakpoint Differences

Group Set Lower Same Higher

“S” TOTALS All in common 135 95 37

> 1 dilution 54 7

Commentary • EUCAST generally more conservative

• >50% are lower • When EUCAST is higher, it is mainly to avoid

splitting the wild-type • “Intermediate” EUCAST much more sparingly

• CLSI usually want to factor in test error

Business Practices

Feature EUCAST CLSI

Organization Co-operative between ESCMID and ECDC

Not-for-profit membership based NGO

History Since 1999 really Started 1968

Funding ESCMID and ECDC Memberships, Sales and some grant funds

Professional involvement Clinicians, Laboratorians, Academics

Academics, Industry, Government (esp. FDA)

Focus Antimicrobial Susceptibility Testing only

Laboratory standards of all types (+ some clinical)

Committees Steering Committee General Committee

Consensus Committee AST Subcommittee AFST Subcommittee VAST Subcommittee

Frequency of meetings 5 times per year 2 times per year

Business Practices

Feature EUCAST CLSI

Consensus process Steering Committee At the meetings, plus check by Consensus Committee

Public consultation Via email and NACs At the meetings

Response to feedback Rapid Rapid

Local representation National AST Committees None specific

Relationship to regulators MOU with EMA Complex: indirect and direct involvement

Relationship to industry Similar to that of the regulator

Complex: indirect and direct involvement

Breakpoints All based on PK-PD wherever possible

PK-PD included only from 2003 – lots await revision

The most notable difference

EUCAST CLSI

$=€=£=0 Minimum $170 USD

per year (For M100)