Expert rules in susceptibility testing EUCAST-ESGARS-EPASG Educational Workshop Linz, 16 19 September, 2014 Dr. Rafael Cantón Hospital Universitario Ramón y Cajal SERVICIO DE MICROBIOLOGÍA Y PARASITOLOGÍA
Antimicrobial susceptibility testing Clinical categorization (S, I, R) Interpretive reading Application of expert rules Based on clinical breakpoints Based on resistance mechanisms knowledge and wild type distributions Based both on clinical evidence and resistance mechanisms knowledge
Antimicrobial susceptibility testing Clinical breakpoints The ultimate goal of clinical breakpoints is using MIC values to separate strains where there is a high likelihood of treatment success (S) from those where treatment is more likely to fail (R) They are not primarily defined to detect resistant bacteria They are mainly derived from prospective human clinical studies comparing outcomes with the MICs of the infecting pathogen and supported with MIC distributions and Pk/Pd studies If breakpoints are well established no actions (expert rules) are needed beyond MIC interpretation This has not been always the case in the past!
Antimicrobial susceptibility testing During more than twenty years interpretive reading of the antibiogram have been used to: - infer resistance mechanisms behind resistant phenotypes - identify resistant organisms for infection control purposes - apply an expert rule* and modify (when needed!) previous clinical categorization Courvalin P. ASM News 19921992;58:368-75 Livermore et al. J Antimicrob Chemother 2001;48(Suppl 1):87-102 Cantón R. Enferm Infecc Microbiol Clin 2002; 20: 176-86 Cantón R. Enferm Infecc Microbiol Clin 2010; 28:375-85 Leclercq et al. Clin Microbiol infect 2011; Oct 21. This approach was partially needed due to inadequate breakpoints! *Action to be taken (normally S or I to R), based on current clinical or microbiological evidence, in response to specific AST results
Antimicrobial susceptibility testing Interpretative reading: the classical example ESBL positive isolate resistant to all cephalosporins and azthreonam (irrespective of MICs) expert rule
Interpretive reading of the antibiogram 1.- To establish the susceptibility phenotype 2.- To infer the potential resistance mechanism 3.- To predict previously defined phenotype from the resistance mechanisms Courvalin P, ASM News, 1992 Livermore DM et al. J Antimicrob Chemother 2001; 48 (Suppl 1): 87-102 Cantón R. Enferm Infecc Microbiol Clin 2010; 28:375-385
Antibiogram interpretative reading Importance of bacterial identification Antimicrobial MIC (mg/l) Ampicillin >64 Amox/clav >32/16 Ticarcillin >64 Piperacillin 32 Piper/Tazo 16/4 Cefuroxime >64 Cefoxitin >32 Cefotaxime 4 Ceftazidime 8 Cefepime 1 Organisms Potential phenoype E. coli AmpC hyperproduction plasmid AmpC ESBL + porin deficiency K. pneumoniae ESBL + porin deficiency E. cloacae ESBL
AMP PIP CEF CXM CAZ FOX CTX AMC FEP ATM Proteus vulgaris Hyperproduction of chromosomal β-lactamase (Class A) IPM Ampicillin Ticarcillin Piperacillin Piper/Tazo Amox/clav Cefalotin Cefoxitin Cefuroxime Cefotaxime Ceftazidime Cefepime Imipenem MIC >256 8->256 8->256 8-32 4-8 >256 2-4 >256 2-8 0,12-0,5 0,5-2 0,5-2 Interp. R R S/R S/R S/I R S R R S S/I S
Stenotrophomonas maltophilia (L1+ L2 enzymes) CTX CPM AMC CAZ ATM
K. pneumoniae OXA -48 + ESBL + ESBL + porin deficiency
Antimicrobial susceptibility testing Clinical categorization (S, I, R) Interpretive reading Application of expert rules Based on clinical breakpoints Based on resistance mechanisms knowledge and wild type distributions Based both on clinical evidence and resistance mechanisms knowledge
EUCAST expert rules: definition Expert rules in antimicrobial susceptibility testing (AST) - describe actions to be taken on the basis of specific AST results - based on clinical breakpoints & resistance mechanism knowledge - assist clinical microbiologists in the interpretation of AST results - contribute to quality assurance by highlighting anomalous results - should be in agreement with clinical breakpoints Winstanley T, Courvalin P. Clin Microbiol Rev 2011; 24: 515 56 Leclercq R et al. Clin Microbiol Infect 2013; 19: 141-60 http://www.eucast.org
Clin Microbiol Infect, 2013; 19:141-60.
EUCAST expert rules The EUCAST expert rules in antimicrobial susceptibility testing are divided into: - intrinsic resistances - exceptional phenotypes - interpretive rules Leclercq R et al. Clin Microbiol Infect 2013; 19: 141-60. http://www.eucast.org
EUCAST expert rules v2: intrinsic resistance Characteristic of all or almost all isolates of the bacterial species The antimicrobial activity of the drug is clinically insufficient or antimicrobial resistance is innate, rendering it clinically useless Antimicrobial susceptibility is unnecessary ECOFF ECOFF www.eucast.org
EUCAST expert rules v2: intrinsic resistance S R ECOFF www.eucast.org
EUCAST expert rules v2: intrinsic resistance Enterobacteriaceae are also intrinsically resistant to benzylpenicillin, glycopeptides, fusidic acid, macrolides (with some exception), lincosamides, streptogramins, rifampicin, daptomycin, and linezolid
EUCAST expert rules v2 Intrinsic resistances affecting Enterobacteriaceae P. rettgeri (but not P. stuartii) produces a chromosomal AAC(2 )-Ia enzyme and should be considered resistant to all aminoglycosides except amikacin and streptomycin. Some isolates express the enzyme poorly and can appear susceptible to netilmicin in vitro, but should be reported as resistant as mutation can result in overproduction of this enzyme All S. marcescens isolates produce a chromosomal AAC(6 )-Ic enzyme that affects the activity of all clinically available aminoglycosides except streptomycin and gentamicin
EUCAST expert rules v2: intrinsic resistance Non-fermentative Gram-negative bacteria are also intrinsically resistant to benzylpenicillin, cefoxitin, cefamandole, ceforuxime, glycopeptides, fusidic acid, macrolides, lincosamides, streptogramins, rifampicin, daptomycin and linezolid
EUCAST expert rules v2: intrinsic resistance Gram-negative bacteria other than Enterobacteriaceae and non-fermentative Gram-negative are also intrinsically resistant to glycopeptides, lincosamides, daptomycin and linezolid R? v3
EUCAST expert rules v2: intrinsic resistance Gram-positive bacteria are also intrinsically resistant to aztreonam, temocillin, polymyxin B/colistin, and nalidixic acid
The EUCAST breakpoints philosophy MIC (mg/l) brpts* Zone (mm) brpts* Insufficient evidence (Literature: not enough evidence for a breakpoint or no indication ) Inappropriate drug (Literature: poor drug don t use! S 2 R>2 mg/l S 22 R<22 mm IE Can not be substituted. Can be supplemented with an MIC without interpretation. Can be substituted with an automatic R *when numbers are the same = no intermediate category Most are intrinsic resistances!
EUCAST breakpoints, 2014 Should be reported as R, if tested!
EUCAST expert rules v2 Exceptional phenotypes Resistances of some bacterial species to particular antimicrobial agents which have not yet been reported or are very rare They should be checked as they may also indicate an error in identification or susceptibility testing. If they are confirmed locally: - the isolate should be further studied - sent to a reference laboratory for independent confirmation The may change with time as resistance may develop and increase over time There may also be local or national differences. Very rare in one hospital, area or country, may be more common in another
EUCAST expert rules v2: exceptional phenotypes This is not the case anymore!
Carbapenemase producing Enterobacteriaceae Europe Cantón et al. Clin Microbiol Infect 2012; 18:413-31 Endemic Interregional spread Regional spread Independent hospital outbreaks Single hospital outbreaks Sporadic occurrence Not reported / no data KPC VIM NDM OXA-48 Other countries: Israel Luxembourg February, 2012 March, 2013 Glasner et al. Euro Surveillance 2013 ; 18(28) doi:pii: 20525
EUCAST expert rules v2 Actions to be taken on the basis of specific AST results Agents tested Agents affected IF THEN Exceptions, scientific basis and comments www.eucast.org
EUCAST expert rules v2: interpretive rules Evidences of expert rules A. There is good clinical evidence that reporting the test results as susceptible leads to clinical failures B. Evidence is weak and based only on a few case reports or on experimental models. It is presumed that reporting the test result as susceptible may lead to clinical failures C. There is no clinical evidence, but microbiological data suggest that clinical use of the agent should be discouraged Leclercq R et al. Clin Microbiol Infect 2013; 19: 141-60 http://www.eucast.org
EUCAST expert rules v2 Evidences A. There is clinical evidence that reporting the test result as susceptible leads to clinical failures
EUCAST expert rules v2 Evidences B. Evidence is weak and based only on a few case reports or on experimental models. It is presumed that reporting the test result as susceptible may lead to clinical failures
EUCAST expert rules v2 Evidences C. There is no clinical evidence, but microbiological data suggest that clinical use of the agent should be discouraged
Clin Microbiol Infect, 2013; 19:141-60.
EUCAST expert rules v3 Revision and update of intrinsic resistance tables - new antibiotics (e.g. ampicillin/sulbactam, aztreonam) - new microorganisms and/or species Update or deletion of exceptional phenotypes (under discussion) - carbapenemase producers,... Expert rules - avoid the presence of antibiotics no longer recommended for testing - oxacillin and S. aureus) - deletion of expert rules with no clinical evidence or weak evidence ( - S. marcescens and aminoglycoside resistance) - reword of expert rules - MLS b resistance mechanisms in gram-positives - new expert rules - glycopeptides and vancomycin/teicoplanin resistance (VanB)?
Acknowledgements
Expert rules in susceptibility testing EUCAST-ESGARS-EPASG Educational Workshop Linz, 16 19 September, 2014 Dr. Rafael Cantón Hospital Universitario Ramón y Cajal SERVICIO DE MICROBIOLOGÍA Y PARASITOLOGÍA