Evaluation of an antimicrobial susceptibility testing system for Aerococcus urinae using DPS192iX

Abstract

In this study, we evaluated the clinical usefulness of an automated antimicrobial susceptibility testing system (DPS192iX, Eiken Chemical Co. Ltd.) for Aerococcus urinae. MICs for nine antimicrobial agents, whose breakpoints were defined in CLSI M45 3rd Edition, were measured using DPS192iX for 38 A. urinae strains isolated and stored in the University of the Ryukyus Hospital between 2014 and 2020 and two ATCC strains, Streptococcus pneumoniae ATCC49619 and A. urinae ATCC51268. Results were compared with MICs determined by a reference method using frozen plates (Eiken Chemical Co., Ltd.). Overall, the ±1 essential agreement (±1 EA) and category agreement (CA) were 94.3% and 97.1%, respectively, whereas the ±1 EA or CA for several agents was less than 90% (±1 EA for ceftriaxone was 85.7%, that for linezolid was 88.6%, and CA for levofloxacin was 85.7%). The minor errors for ciprofloxacin and levofloxacin were 8.6% and 14.3%, respectively, but we did not observe a major error or a very major error. From these observations, the antimicrobial susceptibility testing system DPS192iX is considered useful for A. urinae, although further evaluation is required for several antimicrobial agents such as fluoroquinolones, ceftriaxone, and linezolid.