title: Meropenem/colistin synergy testing for multidrug-resistant Acinetobacter baumannii strains by a two-dimensional gradient technique applicable in routine microbiology.
abstract: OBJECTIVE
  Precise assessment of potential therapeutic synergy, antagonism or indifference between antimicrobial agents currently depends on time-consuming and hard-to-standardize in vitro chequerboard titration methods. We here present a method based on a novel two-dimensional antibiotic gradient technique named Xact™.
  
  
  METHODS
  We used a test comprising a combination of perpendicular gradients of meropenem and colistin in a single quadrant. We compared test outcomes with those obtained with classical chequerboard microbroth dilution testing in a study involving 27 unique strains of multidrug-resistant Acinetobacter baumannii from diverse origins.
  
  
  RESULTS
  We were able to demonstrate 92% concordance between the new technology and classical chequerboard titration using the A. baumannii collection. Two strains could not be analysed by Xact™ due to their out-of-range MIC of meropenem (>128 mg/L).
  
  
  CONCLUSIONS
  The new test was shown to be diagnostically useful, easy to implement and less labour intensive than the classical method.
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France alex.vanbelkum@biomerieux.com.
authors.forename: Alex
authors.initials: A
authors.lastname: van Belkum
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Diane
authors.initials: D
authors.lastname: Halimi
authors.affiliation: Genomic Research Laboratory, Service of Infectious Diseases, Geneva University Hospital (HUG), Geneva, Switzerland.
authors.forename: Eve-Julie
authors.initials: EJ
authors.lastname: Bonetti
authors.affiliation: Bacteriology Laboratory, Service of Infectious Diseases, Geneva University Hospital (HUG), Geneva, Switzerland.
authors.forename: Gesuele
authors.initials: G
authors.lastname: Renzi
authors.affiliation: Bacteriology Laboratory, Service of Infectious Diseases, Geneva University Hospital (HUG), Geneva, Switzerland.
authors.forename: Abdessalam
authors.initials: A
authors.lastname: Cherkaoui
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Sauvonnet
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Roland
authors.initials: R
authors.lastname: Martelin
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Durand
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Sonia
authors.initials: S
authors.lastname: Chatellier
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Zambardi
authors.affiliation: AB BIODISK Research Laboratories, Solna, Sweden Franchise Identification/Antimicrobial Susceptibility Testing, Microbiology Unit, bioMérieux Inc., St Louis, MO, USA.
authors.forename: Anette
authors.initials: A
authors.lastname: Engelhardt
authors.affiliation: Microbiology R&D, Microbiology Unit, bioMérieux SA, La Balme Les Grottes, France AB BIODISK Research Laboratories, Solna, Sweden.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Karlsson
authors.affiliation: Genomic Research Laboratory, Service of Infectious Diseases, Geneva University Hospital (HUG), Geneva, Switzerland Bacteriology Laboratory, Service of Infectious Diseases, Geneva University Hospital (HUG), Geneva, Switzerland.
authors.forename: Jacques
authors.initials: J
authors.lastname: Schrenzel
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004357:Drug Synergism; D000077731:Meropenem; D008826:Microbial Sensitivity Tests / Q000379:methods*; D013845:Thienamycins / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D013845:Thienamycins; D000077731:Meropenem; D003091:Colistin
keywords: antibiotic resistance; susceptibility testing; two-dimensional Etest