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EUCAST version 5.13

Antimicrobial wild type distributions of microorganisms

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

MIC distributions

The website gives MIC distributions for individual organisms and antimicrobial agents in tables and histograms. The distributions are based on collated data from an increasing total of more than 20000 MIC distributions from worldwide sources. Unless otherwise specifically stated, the 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.

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 breakpoints

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

Clinical zone diameter breakpoints

These are shown to the right of the distribution in the tables and the bottom right-hand corner of each histogram in the form S>X/R<Ymm.

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 or WT>Y mm.

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 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@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 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.

What is the source of the data?

The distributions include data 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.

Which MIC determination and disk diffusion methods are represented?

The MIC 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.

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

Has data obtained with a specific method been excluded?

For MIC data 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).

For inhibition zone diameter data, only data generated with quality controlled EUCAST disk diffusion methodology has been included. Thus, the upper part, representing organisms without acquired resistance, can be used to calibrate methodology. The corresponding part of distributions from different laboratories should coincide.   

What is the origin of the organisms included in the 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 breakpoints are made for each group of antibiotics the data are released for public use.

Where can I get more information?

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