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.


EUCAST advice on intrinsic resistance and exceptional phenotypes v 3.2 (February, 2020).

The previous version (3.1 from September, 2016) is savailable 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 (Salmonella spp.) (June, 2019)

Pseudomonas aeruginosa 

Stenotrophomonas maltophilia

Acinetobacter spp.

Staphylococcus spp. (June, 2019)

Enterococcus spp. (June, 2019; Correction November, 2019):

"High level resistance reflect production of ANT(6) or other enzymes or of ribosomal mutations. In vitro studies have shown lack of synergy of betalactams and gentamicin (now changed to streptomycin") in such strains." 

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)