Expert rules and expected phenotypes

Expert rules and expected phenotypes

EUCAST expert rules (see below) are a tabulated collection of expert knowledge on interpretive rules, expected resistant phenotypes and expected susceptible phenotypes which should be applied to antimicrobial susceptibility testing in order to reduce testing, reduce errors and make appropriate recommendations for reporting particular resistances.


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. Grade A required clinical studies supporting the rule.

B. Evidence is weak or based on only a few case reports or on experimental data. Animal studies were accepted as experimental data.

C. There is no clinical evidence, but in vitro microbiological data suggest that the rule should be applied. 


For question and comments on EUCAST expert rules and expected phenotypes, open the EUCAST subject related contact form and choose subject.




Expected phenotypes (follow link)


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 (30 June, 2024); Enterobacterales (January, 2023); Enterobacterales (June, 2019)


Salmonella spp.


Pseudomonas aeruginosa 


Stenotrophomonas maltophilia


Acinetobacter spp.


Staphylococcus spp. (February, 2023)


Enterococcus spp (30 June, 2024); Enterococcus spp. (January, 2023); Enterococcus spp. (June, 2019)


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 v 3.2 (February, 2020)


EUCAST Expert rules v 3.1 (September, 2016)


EUCAST Expert rules (version 2.0 October, 2011)


EUCAST Expert rules (version 1.0 )