title: Evaluation of an Automated System for Reading and Interpreting Disk Diffusion Antimicrobial Susceptibility Testing of Fastidious Bacteria.
abstract: Results of disk diffusion antimicrobial susceptibility testing depend on individual visual reading of inhibition zone diameters. Therefore, automated reading using camera systems might represent a useful tool for standardization. In this study, the ADAGIO automated system (Bio-Rad) was evaluated for reading disk diffusion tests of fastidious bacteria. 144 clinical isolates (68 β-haemolytic streptococci, 28 Streptococcus pneumoniae, 18 viridans group streptococci, 13 Haemophilus influenzae, 7 Moraxella catarrhalis, and 10 Campylobacter jejuni) were tested on Mueller-Hinton agar supplemented with 5% defibrinated horse blood and 20 mg/L β-NAD (MH-F, Oxoid) according to EUCAST. Plates were read manually with a ruler and automatically using the ADAGIO system. Inhibition zone diameters, indicated by the automated system, were visually controlled and adjusted, if necessary. Among 1548 isolate-antibiotic combinations, comparison of automated vs. manual reading yielded categorical agreement (CA) without visual adjustment of the automatically determined zone diameters in 81.4%. In 20% (309 of 1548) of tests it was deemed necessary to adjust the automatically determined zone diameter after visual control. After adjustment, CA was 94.8%; very major errors (false susceptible interpretation), major errors (false resistant interpretation) and minor errors (false categorization involving intermediate result), calculated according to the ISO 20776-2 guideline, accounted to 13.7% (13 of 95 resistant results), 3.3% (47 of 1424 susceptible results) and 1.4% (21 of 1548 total results), respectively, compared to manual reading. The ADAGIO system allowed for automated reading of disk diffusion testing in fastidious bacteria and, after visual validation of the automated results, yielded good categorical agreement with manual reading.
authors.affiliation: Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
authors.forename: Evgeny A
authors.initials: EA
authors.lastname: Idelevich
authors.affiliation: Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Becker
authors.affiliation: Institute of Hygiene, University Hospital Münster, Münster, Germany.
authors.forename: Janne
authors.initials: J
authors.lastname: Schmitz
authors.affiliation: Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Knaack
authors.affiliation: Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Peters
authors.affiliation: Institute of Medical Microbiology, University Hospital Münster, Münster, Germany.
authors.forename: Robin
authors.initials: R
authors.lastname: Köck
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D016123:Campylobacter jejuni / Q000187:drug effects; D006193:Haemophilus influenzae / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000379:methods*; D001936:Moraxella catarrhalis / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents