EUCAST have developed standardised disk diffusion methods for both aerobic and anaerobic bacteria.
EUCAST antimicrobial susceptibility testing is performed with phenotypic methods, reference broth microdilution or standardised disk diffusion. The basis of all susceptibility testing is the minimum inhibitory concentration (MIC). Clinical MIC breakpoints determine whether the organism is categorised as susceptible at normal dosing (S), susceptible at increased exposure (I) or resistant (R) to the agent in question. Derivative methods are calibrated to the reference broth microdilution method at the responsibility of the manufacturer. However, the clinical microbiological laboratory takes full responsibility for the final susceptibility report.
Users of EUCAST breakpoints should use the EUCAST disk diffusion methods below or other susceptibility testing systems calibrated to EUCAST breakpoints and terminology in accordance with EUCAST breakpoint tables.
Quality control document for disk diffusion of aerobic and anaerobic bacteria.
Routine and extended internal quality control for MIC determination and disk diffusion as recommended by EUCAST.
Changes between old and new versions are described in the QC table introduction and marked in the tables.
For previous versions of documents, see the document archive.
In collaboration with the World Health Organisation (WHO), EUCAST publishes instruction videos on how to perform antimicrobial susceptibility testing (AST) using EUCAST recommended methods and interpretation.
The videos are published on Youtube™ and have an English speaker voice and subtitles in different languages. Since not all countries may access Youtube™, videos in some languages are made available directly on this page below.
1. Preparation of inoculum
2. Inoculation
3. Application of disk and incubation
4. Reading of zones
5. Guidance on breakpoint table
6. Storage and handling of media and disks
7. Quality control
1. Preparation of inoculum
2. Inoculation
3. Application of disk and incubation
4. Reading of zones
5. Guidance on breakpoint table
The instruction videos from EUCAST on how to perform antimicrobial susceptibility disk diffusion testing was produced by a project team from EUCAST and WHO:
The following are acknowledged for translations of subtitles into languages other than English:
German
Sören Gatermann, Michael Kresken and Axel Hamprecht, all German NAC.
Russian
Roman Kozlov, Marina Sukhorukova, Mikhail Edelstein, all Institute of Antimicrobial Chemotherapy (IAC), Smolensk State Medical University (SSMU).
Turkish
ADTS working Group (Turkish NAC for EUCAST).
French
Luc Dubreuil, Université de Lille, France.
Spanish
Luis Martinez-Martinez and Antonio Oliver, both Spanish Committee of the Antibiogram (Coesant).
Portuguese/Brazilian
Ana Gales and Jorge Sampaio, Brazilian Committee on Antimicrobial Susceptibility Testing (BrCAST).
Arabic
Magda Rakha, Consultant Public Health laboratories and Humayun Asghar, WHO EMRO.
Czech
Pavla Urbaskova, Helena Zemlickova and Vladislav Jakubu, all members of the Czech NAC.
Chinese
Yu Qing Liiu, member of the Chinese NAC, and Hong Yin, clinical microbiology, Falun, Sweden.
Romanian
Olga Burduniuc (Chair of Moldovan NAC)
In some of the informational videos colleagues are advised to categorise the susceptibility of bacteria without breakpoints using the PK/PD breakpoints (previously available from the EUCAST breakpoint tables). This is no longer acceptable since the current opinion is that the PK/PD cut-off values may vary between species and EUCAST has therefore removed the PK/PD tab from the breakpoint table 14.0 (1 January, 2024). Instead we refer the EUCAST user to the guidance document “When there are no breakpoints” among the guidance documents.
The EUCAST Development Laboratory has systematically investigated the quality of MH-powders, antibiotic disks and of pre-poured MH plates for disk diffusion.
Letter To European laboratories
How the IVDR affects users of EUCAST recommendations
Alternative media for fastidious organisms in EUCAST disk diffusion testing
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