A-273 Multicenter Assessment of the Accuracy of MIC Results for Piperacillin/Tazobactam with MicroScan Dried Gram-Negative MIC Panels using CLSI Breakpoints

Abstract Background MIC data from MicroScan Dried Gram-negative MIC (MSDGN) Panels with piperacillin/tazobactam were evaluated with CLSI-M100-ED32 breakpoints for Acinetobacter, Enterobacterales, Other-Non-Enterobacterales, and proposed CLSI breakpoints for Pseudomonas aeruginosa from a multicenter clinical study. MIC results were compared to results obtained with CLSI frozen broth microdilution panels. Materials/Methods The study included a total of 683 clinical isolates tested using Prompt and turbidity during efficacy and challenge phases. MSDGN panels were evaluated at three clinical sites, comparing MIC values obtained using MSDGN panels to MICs utilizing CLSI reference panel. MSDGN panels were incubated at 35 ± 1°C and read on WalkAway System, autoSCAN-4 instrument, and read visually at 16–20 h. Frozen reference panels were prepared according to CLSI methodology, incubated for 16–20 h for Enterobacterales, Other Non-Enterobacterales, and Pseudomonas aeruginosa and for 20–24 h for Acinetobacter and read visually. CLSI breakpoints(mg/L) used for interpretation of MIC results were: ≤16/4 S, 32/4–64/4 I, ≥128/4 R for Acinetobacter and Other Non Enterobacterales, ≤8/4 S, 16/4 SDD, ≥32/4 R for Enterobacterales, and ≤16/4 S, 32/4 I, >64/4 R for Pseudomonas aeruginosa. Results When compared to frozen reference panel results, essential and categorical agreements for all isolates tested are as follows with these recommendations: Due to elevated major error rates for S. marcescens and WalkAway reads with Prompt, results should be confirmed visually prior to reporting. Due to performance with P. rettgeri and S. liquefaciens complex, do not report drug, therapy, or MIC. Conclusion Piperacillin/tazobactam MIC results for gram-negative clinical isolates obtained with the MSDGN panel correlate with MICs obtained using frozen reference panels with updated CLSI interpretive criteria.