667. Multicenter Assessment of Enterobacterales, Salmonella spp. and Pseudomonas aeruginosa Using Updated CLSI Levofloxacin Breakpoints on MicroScan Dried Gram Negative MIC Panels

Abstract Background Data from a multicenter clinical study with Enterobacterales, Salmonella spp. and P. aeruginosa on a MicroScan Dried Gram-negative MIC (MSDGN) Panel was evaluated with updated US FDA/CLSI levofloxacin breakpoints. MIC results were compared to results obtained with frozen broth microdilution panels prepared according to CLSI methodology. Methods A total of 839 Enterobacterales, Salmonella spp. and P. aeruginosa clinical isolates were tested at three clinical sites in efficacy and challenge combined. MSDGN panels were evaluated with turbidity and Prompt® methods of inoculation. MIC values obtained from the MSDGN panels were compared to MICs utilizing a CLSI broth microdilution reference panel. To assess reproducibility, a subset of 15 organisms were tested on MSDGN panels at each site. MSDGN panels were incubated at 35 ± 1ºC and read on the WalkAway System, the autoSCAN-4 instrument, and visually. Read times for the MSDGN panels were at 16-20 hours. Frozen reference panels were prepared and read according to CLSI methodology. FDA and CLSI breakpoints (µg/mL) used for interpretation of MIC results were: Enterobacterales ≤ 0. 5 S, 1 I, ≥ 2 R; Salmonella spp. ≤ 0.12 S, 0.25-1 I, ≥ 2 R; P. aeruginosa ≤ 1 S, 2 I, ≥ 4 R. Results Essential and categorical agreement were calculated compared to frozen reference panel results. Results for isolates tested during efficacy and challenge with Prompt inoculation and manual read are as follows: Conclusion Levofloxacin MIC results for Enterobacterales, Salmonella spp., and P. aeruginosa obtained with the MSDGN panel correlate well with MICs obtained using frozen reference panels using updated FDA/CLSI interpretive criteria in this multicenter study. * PROMPT® is a registered trademark of 3M Company, St. Paul, MN USA. BEC, the stylized logo and the BEC product and service marks mentioned herein are trademarks or registered trademarks of Beckman Coulter, Inc. in the US and other countries. Disclosures Omai Garner, PhD, D(ABMM), Beckman Coulter (Scientific Research Study Investigator) Maria M. Traczewski, BS MT (ASCP), Beckman Coulter (Scientific Research Study Investigator) Denise Beasley, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Amanda Harrington, PhD, Beckman Coulter (Scientific Research Study Investigator) Sharon DesJarlais, BS, Beckman Coulter (Other Financial or Material Support, Research personnel) Christine Hastey, PhD, Beckman Coulter (Employee) Regina Brookman, BS, Beckman Coulter (Employee) Zabrina Lockett, MS, Beckman Coulter (Employee) Jennifer Chau, PhD, Beckman Coulter (Employee)