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MIC and Inhibition zone diameter distributions of microorganisms without and with phenotypically evident resistance mechanisms

MIC and inhibition zone diameter distributions

Distributions are shown as "aggregated distributions" and as "aggregated weighted distributions". For aggregated distributions all accepted distributions (as defined in SOP 10) were added to form one common distribution. For aggregated weighted distributions each individual distribution was converted to contribute equally to the common aggregated distribution. In this way large distributions are prevented from drowning out smaller distributions.

1. MIC distributions

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

2. 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 - see www.eucast.org).

Clinical MIC and Zone diameter breakpoints

These are not shown on this website – please consult the EUCAST breakpoint tables for bacteria and fungi on www.eucast.org.

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.

To cite data from the EUCAST program

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

To contribute MIC- or zone diameter distribution data

Please send data to gunnar.kahlmeter@eucast.org or Jenny.ahman@eucast.org. We propose you download from the EUCAST website (https://www.eucast.org/mic_distributions_and_ecoffs/) and use one of the Excel files for bacteria or fungi and follow the instructions in the spreadsheet.

Frequently asked questions

What is the purpose of the MIC distributions?

• 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

What is the source of the data?

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.

Which MIC determination and disk diffusion methods are represented?

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.

Have data obtained with a specific method been excluded?

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).

What is the origin of the organisms included in the data?

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

What does "No Data available" imply?

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.

Where can I get more information?

Contact EUCAST via the EUCAST Contact form. In addition, email addresses and further information can be obtained through the EUCAST website at https://www.eucast.org.