Phenotypic antimicrobial susceptibilities are particularly valuable for P. aeruginosa due to the complexity of resistance mechanisms this organism can harbor.…

BackgroundThe Clinical and Laboratory Standards Institute (CLSI) updated fluoroquinolone breakpoints in 2019 in response to evolving resistance and new outcome data. The performance of updated antimicrobial susceptibility testing (AST) algorithms for ciprofloxacin with the 2019 breakpoints for Enterobacteriaceae and Pseudomonas aeruginosa was evaluated using the Accelerate Pheno™ system with contrived positive blood culture samples compared with broth microdilution (BMD).MethodsA total of 294 clinical isolates (100 P. aeruginosa, 82 Klebsiella spp., 56 E. coli, 24 Citrobacter spp., 14 Enterobacter spp., 15 Proteus spp., and 3 S. marcescens) were tested with ciprofloxacin. Aliquots of BD BACTEC™ Standard Aerobic media containing healthy donor blood were seeded with 10–100 bacterial cells and incubated until positivity. Aliquots of the positive blood cultures were run using the Accelerate PhenoTest™ BC kit on the Accelerate Pheno™ system according to the manufacturer instructions for use. Results were obtained using an updated ciprofloxacin algorithm and compared with CLSI standard reference BMD. Only samples with valid results with both the Accelerate Pheno™ system and reference BMD were included in analysis. Essential agreement (EA), categorical agreement (CA), very major error (VME), major error (ME) and minor error (mE) rates were calculated using 2019 CLSI breakpoints.ResultsEA and CA for all antimicrobial/organism combinations were >94%. There were 2 MEs (1 K. pneumoniae, 1 C. freundii) and no VMEs.ConclusionResults with the new research use only (RUO) algorithms are very good and meet FDA acceptance criteria for AST performance. These data will be submitted to the FDA for clearance, once FDA recognizes the CLSI breakpoints. Disclosures All authors: No reported disclosures.

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