MIC and zone diameter distributions

The website gives MIC and zone diameter distributions for individual organisms and antimicrobial agents in tables and wild type distributions in histograms. The MIC distributions are based on collated data from an increasing total of close to 20000 MIC distributions from worldwide sources. From December 2009 zone diameter distributions will be added and will be expanded rapidly. Unless otherwise specifically stated, the MIC data are representative of results obtained with a variety of MIC methods. 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 and between different methods. Zone diameter distributions are all based on the standardised EUCAST disk diffusion method (http://www.eucast.org/eucast_disk_diffusion_test/disk_diffusion_methodology/).

Clinical MIC and zone diameter breakpoints

These are shown to the right of the MIC or zone diameter distribution in the tables and the bottom right-hand corner of each histogram in the form S<X/R>Y mg/L for MICs or S>X/R<Y mm for zone diameters.

The epidemiological cut-off value (ECOFF)

This separates microorganisms without (wild type) and with 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 histogram in the form WT<X mg/L for MICs or WT>X mm for zone diameters.

Limitations

Different studies use different MIC ranges, which may particularly affect the upper part of the MIC ranges. Distributions with severely truncated MIC distributions are not included. Also the collated distributions include studies from a wide variety of sources and time periods and some include high 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.

To cite data from the EUCAST program

We suggest the format "European Committee on Antimicrobial Susceptibility Testing. Data from the EUCAST MIC and zone diameter distribution website, last accessed Day Month Year”. http://www.eucast.org"

To contribute MIC distribution data

Please send data to gunnar.kahlmeter@ltkronoberg.se. It is much appreciated if you download and use one of the Excel files for bacteria or fungi, following the instructions in the spreadsheet.

Frequently asked questions

What is the purpose of the MIC and zone diameter distributions?

• reference material for committees involved in decisions on clinical breakpoints

• reference material for epidemiological cut-off values for antimicrobial resistance surveillance

• reference MIC and zone diameter ranges of wild type organisms for a wide spectrum of species and antimicrobials

• international reference for calibration of antimicrobial susceptibility testing methods.

What are the sources of the data?

The distributions include MICs from national and international studies such as the BSAC, NORM, SENTRY, MYSTIC and GENARS resistance surveillance programmes, as well as MIC distributions from published articles, the pharmaceutical industry, veterinary programmes and individual laboratories. Zone diameter distributions are from studies in reference laboratories using the standardised EUCAST disk diffusion method.

Which MIC determination methods are represented?

The distributions represent MIC values determined with methods described by ISO, EUCAST, BSAC (UK), CA-SFM (France), CRG (The Netherlands), DIN (Germany), NWGA (Norway), SRGA (Sweden) and CLSI (USA). Commercial MIC determination methods standardized to any of the recognised methods are also included.

Has data obtained with a specific MIC method been excluded?

No specific method has been excluded. Contributions are screened by the EUCAST Steering Committee and less than 10% have been excluded from the aggregated distributions. However, all data are held in the database and are accessible to the Steering Committee. The most common reason for exclusion has been that the MIC ranges were truncated (not full-range) so that a significant proportion of MICs were outside the tested range (especially when at the low end of the distribution).

What is the origin of the organisms included in the MIC and zone diameter data?

The data are from tests on bacteria and fungi collected from man and animals, of any geographic origin and over a wide timeframe.

What does "Data not released for public use" imply?

Some of the antimicrobials in the pull-down list are followed by the text "data not released for public use". 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 MIC breakpoints are made for each group of antibiotics the data are released for public use. Zone diameter distributions are released as EUCAST zone diameter breakpoints are released.

Where can I get more information?

Contact EUCAST – email addresses and information can be obtained through the EUCAST website at http://www.eucast.org.