title: Evaluation of paper gradient concentration strips for antifungal combination testing of Candida spp.
abstract: In vitro combination testing with broth microdilution chequerboard (CHEQ) method is widely used although it is time-consuming, cumbersome and difficult to apply in routine setting of clinical microbiology laboratory. A new gradient concentration paper strip method, the Liofilchem(®) MIC test strips (MTS), provides an alternative easy and fast method enabling the simultaneous diffusion of both drugs in combination. We therefore tested a polyene+azole and an azole+echinocandin combination against 18 Candida isolates with the CHEQ method based on EUCAST guidelines and the MTS method in research and routine settings. Fractional inhibitory concentration (FIC) indices were calculated after 24 and 48 h of incubation based on complete and prominent (FIC-2) growth inhibition endpoints. Reproducibility and agreement within 1 twofold dilution was assessed. The FICs of the two methods were correlated quantitatively with t-test and Pearson analysis and qualitatively with Chi-squared test. The reproducibility of the CHEQ and MTS method was 88-100% and their agreement was 80% with 62-77% of MTS FICs being higher than the corresponding CHEQ FICs. A statistically significant Pearson correlation (r = 0.86, P = 0.0003) and association (χ(2) = 17.05, df = 4, P = 0.002) was found between MTS FIC and CHEQ FIC-2 after 24 h. Categorical agreement was 63% with no very major or major errors. All MTS synergistic interactions were also synergistic with the CHEQ method.
authors.affiliation: Clinical Microbiology Laboratory, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Siopi
authors.affiliation: Clinical Microbiology Laboratory, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Siafakas
authors.affiliation: Clinical Microbiology Laboratory, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: Loukia
authors.initials: L
authors.lastname: Zerva
authors.affiliation: Clinical Microbiology Laboratory, Attikon University Hospital, Medical School, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: Joseph
authors.initials: J
authors.lastname: Meletiadis
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology; D000935:Antifungal Agents / Q000494:pharmacology*; D001393:Azoles / Q000494:pharmacology; D002175:Candida / Q000187:drug effects* / Q000254:growth & development; D002177:Candidiasis / Q000382:microbiology*; D000077336:Caspofungin; D016009:Chi-Square Distribution; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D054714:Echinocandins / Q000494:pharmacology; D006801:Humans; D055666:Lipopeptides; D008826:Microbial Sensitivity Tests / Q000379:methods*; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D065819:Voriconazole / Q000494:pharmacology
chemical_list: D000935:Antifungal Agents; D001393:Azoles; D054714:Echinocandins; D055666:Lipopeptides; D011933:Reagent Kits, Diagnostic; D000666:Amphotericin B; D000077336:Caspofungin; D065819:Voriconazole
keywords: Candida; chequerboard; combination; gradient concentration strips; in vitro antifungal susceptibility