Expert rules and intrinsic resistance

Expert rules and intrinsic resistance

EUCAST expert rules are a tabulated collection of expert knowledge on intrinsic resistances, exceptional resistance phenotypes and interpretive rules that may be applied to antimicrobial susceptibility testing in order to reduce errors and make appropriate recommendations for reporting particular resistances.


For question and comments on EUCAST expert rules and intrinsic resistance, use the EUCAST subject related contact form. 

EUCAST advice on intrinsic resistancde and exceptional phenotypes v 3.3 (4 January, 2022). The revised version 3.3 corrects a few errors discovered in the document published on 18 October, 2021).

Rules are graded according to A, B and C:

A. There is good clinical evidence for the rule, i.e., applying the rule likely improves patient care.
B. Evidence is weak or based on only a few case reports or on experimental data. 
C. There is no clinical evidence, but in vitro microbiological data suggest that rule should be applied. 


The  previous version (v 3.2) (from February, 2020).is available for comparison.
The previous version (v 3.1) (from September, 2016) is available for comparison.  

Expert rules, all documents revised 2019. Following the revision and a period of public consultation, the revised rules are now published as separate documents, each corresponding to a tab in the breakpoint table. Species listed without a link to a document lack expert rules. Documents may be updated separately why dates may eventually differ between documents.


Enterobacterales (June, 2019; typographical corrections October, 2021)

Salmonella spp.

Pseudomonas aeruginosa 

Stenotrophomonas maltophilia

Acinetobacter spp.

Staphylococcus spp. (June, 2019)

Enterococcus spp. (June, 2019; correction May, 2020):

Streptococcus A, B, C and G  (June, 2019)

Streptococcus pneumoniae  (June, 2019)

Viridans Group Streptococci (June, 2019)

Haemophilus influenzae (June, 2019)

Moraxella catarrhalis (June, 2019)

Neisseria gonorrhoeae

Neisseria meningitidis

Anaerobes, grampositive

Clostridium difficile

Anaerobes, gramnegative

Helicobacter pylorii

Listeria monocytogenes

Pasteurella multocida 

Campylobacter jejuni and C.coli (June, 2019)

Corynebacterium spp. (June, 2019)

Aerococcus sanguinicola and urinae

Kingella kingae

Aeromonas spp.

Mycobacterium spp.


For Stenotrophomonas maltophilia and Burholderia cepacia complex, see Guidance documents 



EUCAST Expert rules, intrinsic resistance and exceptional phenotypes v 3.1 (Sept 27, 2016)

EUCAST Expert rules (version 2.0 valid until Sept 10, 2016)

EUCAST Expert rules (version 1.0 valid until 29 Oct, 2011)