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MIC and Zone Distributions, ECOFFs

Visit MIC EUCAST

The database of MIC and zone diameter distributions was created by Gunnar Kahlmeter for EUCAST from 2002 and onwards. More data is regularly added and all data is curated by Gunnar Kahlmeter and John Turnidge. 

The website gives MIC distributions and inhibition zone diameter distributions for individual micro-organisms (bacteria and fungi) and antimicrobial agents in tables and histograms.

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MIC distributions

The distributions are based on collated data from an increasing total of more than 30 000 MIC distributions from worldwide sources. Unless otherwise specifically stated, the data are representative of results obtained with MIC methods performed by or calibrated to reference broth microdilution using ISO-20776-2. Different methods do not give exactly the same results, but the results rarely vary by more than one doubling dilution step. In this way the aggregated MIC distributions encompass the variation between different investigators, laboratories, geographic locations and time periods.

Inhibition zone diameter distributions

The website gives inhibition zone diameter distributions for individual organisms and antimicrobial agents in tables and histograms. The distributions are based on collated data from an increasing number of sources worldwide. The data are representative of results obtained with the EUCAST disk diffusion method (launched in 2009).

Epidemiological cut-off values (ECOFF) and tentative epidemiological cut-off values (TECOFF)

ECOFFs (and TECOFFs) distinguish microorganisms without (wild type) and with phenotypically detectable acquired resistance mechanisms (non-wild type) to the agent in question. The epidemiological cut-off value is shown in the tables and the bottom left-hand corner of each MIC and zone diameter graph. TECOFFs (ECOFFs in parentheses) are based on 3 or 4 distributions and ECOFFs on at least 5 and up to 100 or more distributions.

Limitations

  • The database is being curated in accordance with EUCAST SOP 10.
  • Different studies often use different MIC concentration ranges.
  • Distributions truncated at the lower end of the scale within the putative wild-type distribution have been excluded. The accepted distributions include studies from a wide variety of sources and time periods and some, on purpose, include high and others low, proportions of resistant organisms, so the distributions must not be used to represent rates of resistance to any agent and cannot be used to compare resistance rates among agents, resistance over time or resistance in different geographic locations.

Contributions of MIC and Zone diameter distributions

Contributions of MIC and Zone diameter distributions are welcomed by EUCAST and can be made using the following Excel file templates: 

The curators of the database are currently Gunnar Kahlmeter, Erika Matuschek, Jenny Åhman and John Turnidge.

Submit your contributions to Gunnar Kahlmeter or Erika Matuschek.

Frequently asked questions

  • reference material for committees involved in decisions on clinical breakpoints
  • reference material for epidemiological cut-off values for antimicrobial resistance surveillance
  • reference MIC ranges of wild type organisms for a wide spectrum of species and antimicrobials
  • international reference for calibration of antimicrobial susceptibility testing methods. If your distribution indicate a different wild type and ECOFF value than that in the database, as evidenced by a putative wild-type modal 2 or more two-fold dilutions different from the mode of the website’s aggregated distributions, you probably made a mistake, used inadequate material or have used a method that is neither the reference method or one calibrated to it
  • ECOFFs can be used for antimicrobial resistance surveillance purposes, especially when other breakpoints are poorly defined or change over time

The distributions include data from national and international studies and resistance surveillance programs, as well as MIC distributions from published articles, the pharmaceutical industry, veterinary programs and individual laboratories.

The MIC distributions represent MIC values primarily determined with methods described by EUCAST and CLSI using ISO 20776-1 (ISO 16256 for fungi). Other MIC-determination methods clearly calibrated to any of the reference methods using ISO-20776-2 are also included. Where no internationally agreed reference method exists, the distributions are labelled according to the method used.

The zone diameter distributions are based on inhibition zones generated through the EUCAST disk diffusion method only.

For MIC data, no specific method has been excluded. Contributions are screened by the EUCAST Subcommittee on Wild Type distributions and ECOFFs and typically 10 - 20% have been excluded from the aggregated distributions, the most common reason being "lower end truncation". However, all data are held in the database and are accessible for discussion.

For inhibition zone diameter data, only data generated with quality-controlled EUCAST disk diffusion methodology have been included. Thus, the upper part, representing organisms without acquired resistance, can be used to calibrate methodology. The wild-type distribution generated in individual laboratories should match the wild type distributions on the EUCAST website (mode within one two-fold dilution).

The data are from bacteria and fungi collected from man and animals, of any geographic origin and over a period of 70 years.

For some of the antimicrobials in the pull-down list no data is available for public view ("No Data available"). The process of harmonizing clinical breakpoints across Europe and of defining the epidemiological cut-off values is co-ordinated with the collection of relevant MIC data. As decisions on breakpoints are made and the quality of data have been assessed for each group of antimicrobials the data are released for public use.

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