title: Performance of EUCAST and CLSI approaches for co-amoxiclav susceptibility testing conditions for clinical categorization of a collection of Escherichia coli isolates with characterized resistance phenotypes.
abstract: OBJECTIVE
  There are different methodological recommendations for in vitro testing of the co-amoxiclav combination. Performance of co-amoxiclav MIC testing for Escherichia coli by the standard ISO microdilution method (ISO 20776-1) was compared using EUCAST (fixed 2 mg/L clavulanate concentration) and CLSI (2 : 1 ratio) interpretive criteria.
  
  
  METHODS
  MICs were determined by broth microdilution using a 2 : 1 ratio and fixed clavulanate concentrations (2 and 4 mg/L) for 160 clinical E. coli isolates with characterized resistance mechanisms. Essential agreements, categorical agreements and relative errors were determined.
  
  
  RESULTS
  For all isolates, essential agreement between microdilution using 2 mg/L clavulanate and a 2 : 1 ratio was 25.6%. For ESBL-producing isolates, considering EUCAST breakpoints, 55% of isolates tested with 2 mg/L clavulanate were classified as resistant; conversely, 95% of isolates tested with 4 mg/L clavulanate were susceptible. When using CLSI breakpoints and a 2 : 1 ratio, 90% of isolates were susceptible and 10% were intermediate.
  
  
  CONCLUSIONS
  Variation in the clavulanate concentration gave different susceptibility testing results, particularly among ESBL-producing E. coli isolates. The in vitro concentration of clavulanate that better correlates with clinical outcome is still under debate and should be established.
authors.affiliation: Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Díez-Aguilar
authors.affiliation: Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: María-Isabel
authors.initials: MI
authors.lastname: Morosini
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología, Hospital Universitario Virgen Macarena and Departamento de Microbiología, Universidad de Sevilla, Sevilla, Spain.
authors.forename: Lorena
authors.initials: L
authors.lastname: López-Cerero
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología, Hospital Universitario Virgen Macarena and Departamento de Microbiología, Universidad de Sevilla, Sevilla, Spain.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Pascual
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología, Hospital Universitario Marqués de Valdecilla-IDIVAL, Santander, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Calvo
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología, Hospital Universitario Marqués de Valdecilla-IDIVAL, Santander, Spain Departamento de Biología Molecular, Universidad de Cantabria, Santander, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Martínez-Martínez
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología Clínica, Hospital Clínic, Facultad de Medicina and Centro de Investigación en Salud Internacional de Barcelona (CRESIB), Barcelona, Spain.
authors.forename: Francesc
authors.initials: F
authors.lastname: Marco
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Servicio de Microbiología Clínica, Hospital Clínic, Facultad de Medicina and Centro de Investigación en Salud Internacional de Barcelona (CRESIB), Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Vila
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Laboratorio de Antibióticos, Bacteriología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Adriana
authors.initials: A
authors.lastname: Ortega
authors.affiliation: Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain Laboratorio de Antibióticos, Bacteriología, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Oteo
authors.affiliation: Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain Red Española de Investigación en Patología Infecciosa (REIPI) Instituto de Salud Carlos III, Madrid, Spain rafael.canton@salud.madrid.org.
authors.forename: Rafael
authors.initials: R
authors.lastname: Cantón
mesh_terms: D019980:Amoxicillin-Potassium Clavulanate Combination / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D010641:Phenotype
chemical_list: D000900:Anti-Bacterial Agents; D019980:Amoxicillin-Potassium Clavulanate Combination
keywords: E. coli; MICs; amoxicillin/clavulanate