Correlation of Vitek 2 and Agar dilution for levofloxacin susceptibility testing and clinical outcomes of Enterobacterales bacteremia with 2019 CLSI breakpoints

Abstract

In 2019, the CLSI lowered the susceptible levofloxacin breakpoints for Enterobacterales from a MIC of ≤2 μg/mL to ≤0.5 μg/mL. The study evaluated the correlation between the susceptibility profiles obtained by the Vitek 2 and agar dilution (AD) methods in levofloxacin MIC ≤2 μg/mL isolates and its clinical impacts. Two hundred fifty-three Enterobacterales isolates and 222 patients treated with levofloxacin for Enterobacterales bacteremia were enrolled for analysis. There was 86.2% categorical agreement, 5 very major errors, and 30 minor errors based on the 2019 CLSI breakpoints. Higher levofloxacin MICs (1 or 2 μg/mL) determined using Vitek 2 or AD predicted early clinical failure (P < 0.001 for Vitek 2 and P = 0.001 for AD). In conclusion, Vitek 2 performance for levofloxacin susceptibility testing of Enterobacterales declined according to the 2019 CLSI criteria compared with the pre-2019 criteria. Although discrepant results were obtained, the MICs measured by Vitek 2 could still predict treatment outcomes.

Keywords: CLSI breakpoints; Enterobacterales; Levofloxacin susceptibility; Vitek 2; agar dilution.