Performance evaluation of plazomicin susceptibility testing of Enterobacterales on VITEK 2 and VITEK 2 Compact Systems.

The objective of the present study was to evaluate the VITEK 2 antimicrobial susceptibility test (AST) for Gram-negative (GN) plazomicin performance using the VITEK 2 and VITEK 2 Compact Systems in clinical settings and to demonstrate its equivalence to the Clinical and Laboratory Standards Institute (CLSI) broth microdilution (BMD) technique. The clinical study conducted at four external sites followed the requirements detailed in the US Food and Drug Administration (FDA) and International Standards Organization (ISO) guidance documents and included clinical, challenge, quality, and reproducibility studies. In this multisite study, a total of 979 Enterobacterales isolates were tested. The VITEK 2 card minimum inhibitory concentration (MIC) results were compared with the reference BMD MIC results. The performance following ISO criteria indicated Essential Agreement (EA) = 97.8% and showed that VITEK 2 plazomicin MIC results for Enterobacterales tend to be in exact agreement when compared with the CLSI BMD reference method, except for Escherichia coli, when MICs tend to be in exact agreement or at least one doubling dilution lower. The analysis was also performed following the FDA criteria using the breakpoints defined by the FDA: ≤2 susceptible (S), 4 intermediate (I), and ≥8 resistant (R) for Enterobacterales. The analysis showed the following performance: EA = 98.7%, category agreement (CA) = 99.4%, and major errors (ME) = 0.1%, with no very major errors (VME) present. There are three species, Klebsiella pneumoniae, Escherichia coli, and Serratia marcescens, for which the trend is ≥ 30% and therefore addressed as a note in the US label. The plazomicin test met the ISO and FDA criteria of ≥95% reproducibility and ≥95% quality control (QC) results within acceptable ranges for QC organisms.IMPORTANCEThe VITEK 2 AST-GN plazomicin test is a new, automated alternative to the BMD reference method for determining minimum inhibitory concentrations (MIC) of Enterobacterales, expanding the range of automatic AST testing.