title: Comparison of 3 Etest(®) methods and time-kill assay for determination of antimicrobial synergy against carbapenemase-producing Klebsiella species.
abstract: Increasing global antibiotic resistance has resulted in more use of antibiotic combinations. There is a lack of a gold standard for in vitro testing of these combinations for synergy or antagonism. Time-kill assay (TKA) may be used but is labor intensive and not practical for clinical use. Etest® synergy methods are more rapid and easier to perform, but there is no agreement regarding which method is best. We tested 31 clinical genetically unique Klebsiella pneumoniae carbapenemase-producing Klebsiella isolates with the combination of meropenem and polymyxin B by TKA and 3 Etest methods, each in triplicate: Method 1, MIC:MIC; Method 2, direct overlay; and Method 3, cross. Overall, testing with Etest synergy methods showed the following agreement with TKA: Method 1: 25/31 (80.6%), Method 2: 7/31 (22.6%), and Method 3: 8/31 (25.8%). The MIC:MIC method had the highest agreement (80.6%, κ = 0.59, P < 0.001) and should be evaluated more extensively.
authors.affiliation: Infectious Disease Research, Ochsner Clinic Foundation, New Orleans, LA, USA. Electronic address: gpankey@ochsner.org.
authors.forename: George A
authors.initials: GA
authors.lastname: Pankey
authors.forename: Deborah S
authors.initials: DS
authors.lastname: Ashcraft
authors.forename: Adriana
authors.initials: A
authors.lastname: Dornelles
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism*; D004357:Drug Synergism; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests / Q000379:methods*; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001618:beta-Lactamases; C063912:carbapenemase
keywords: Etest; Klebsiella; Synergy