Methods: The study isolates included 125 Enterobacteriaceae (12 species as shown in the table), which were chosen to include a range of plazomicin MICs and isolates with known resistant mechanisms. Each isolate was tested for PLZ MIC by broth microdilution (BMD; LSI prepared frozen panels) and by PLZ MTS on 100 mm Mueller Hinton agar (MHA) plates (Becton Dickinson, Sparks, MD) and a subset of 20 strains was also tested on MHA plates from two additional manufacturers (Hardy, Santa Maria, CA and Remel, Lenexa, KA). Quality control (QC) strains (E. coli ATCC 25922 and P. aeruginosa ATCC 27853) were tested on each day of testing and results compared to CLSI expected ranges.
Results: As shown in the table, PLZ MTS and BMD results were within +/- one doubling dilution (essential agreement) for 99.2% of all study isolates. The category agreement rate was 91.2% (based on proposed susceptible/intermediate/resistant breakpoints of ≤4/8/≥16 µg/mL) and there were no very major or major errors observed. The QC results were within CLSI published ranges. PLZ results for MTS tested on Remel and Hardy MHA for the subset of 20 isolates were similar to BD MHA results (equivalent or 1 dilution lower).
Table: Comparison of Plazomicin MIC results (frequency
distribution of dilution difference, MTS MIC–BMD MIC)
|Organism||Dilution Difference by Organism|
Conclusion: This initial evaluation of the plazomicin MTS showed good correlation to BMD MIC. Further testing with additional isolates and media at multiple test sites is warranted.
A. W. Serio, None