Prospective Evaluation of Accelerate Pheno™ System (AXDX) Version 1.1 for Reducing Turn-Around-Time (TAT) in Identification/Antimicrobial Susceptibility Testing (ID/AST) of Gram-Negative Bacilli (GNB) from Positive Blood Cultures (+BC) using AXDX PhenoTest™ BC Kits

Abstract

BackgroundThis study evaluated AXDX (uses FISH/real-time microscopy to obtain ID/AST direct from +BC in <7h) for accuracy against reference mass spectrometry (MS, VITEK® MS, bioMérieux) and broth microdilution (BMD), respectively. AXDX TAT was timed against current reporting for ID using MS and VITEK®2 (VT2, bioMérieux) for AST (VT2 data not presented).MethodsBlood from 173 semi-consecutive +BC tested in BacT/Alert® (bioMérieux) with GNB on Gram were tested in AXDX. Susceptible/intermediate/resistant (S/I/R) interpretations were as per CLSI-M100-S27 for cefazolin (CFZ), ceftriaxone (CRO), ceftazidime (CAZ), piperacillin/tazobactam (TZP), ertapenem (ETP), meropenem (MEM), ciprofloxacin (CIP), gentamicin (GM), tobramycin (TOB), and amikacin (AN). ID and AST results were combined across GNB-genera for assessment as per Cumitech 31A for ≥90% agreements [identificatoin, essential (EA); categorical (CA)] and errors [very major (VME) <3%; combined major/minor (ME/mE) <7%].Results142 (82.1%) AXDX results were evaluable (ID-agreed/AST-reported) for 78 Escherichia coli, 27 Klebsiella species, 17 Pseudomonas aeruginosa, 5 Enterobacter cloacae, 8 Serratia marcescens, 3 Proteus mirabilis, 2 Acinetobacter baumannii and 2 Citrobacter freundii as seen tabulated below. Limits were exceeded for underlined values but 95% confidence intervals (CI) overlapped acceptable limits except in values marked with asterisks [EA (CAZ: 68.7–82.7), ME/mE (CFZ: 5.1–16.8; CAZ: 10–21.9; TZP: 9.2–20.8)]. VME were not evaluable (NE) for TZP, ETP, MEM, or AN due to insufficient numbers of GNB resistant to these agents.ID/AST TAT means (ranges) for AXDX were 1:21h (1:19–1:24h)/6:38h (6:30–6:59h) conmpared to MS/VT2 of 8:49h (2:49–76:48h)/38:23h (19:44–64:22h), respectively; paired t-tests, P < 0.0001/P < 0.0001; difference of means: 8:17h (95% CI:6:55–9:38h)/28:41h (95% CI:26:53–30:29h)].ConclusionThese data suggest AXDX will significantly reduce ID/AST TAT in GNB bacteremia (ID: 8:49h to 1:21h; AST: 38:23h to 6:38h) with potential to significantly improve patient outcomes. Acceptable accuracy was achieved for ID and AST for most agents. A limitation was the lack of GNB causing bacteremia with resistance to AN, TZP, ETP or MEM in during evaluation.Disclosures B. M. Willey, Mount Sinai Hospital: Investigator, Educational support S. M. Poutanen, Accelerate Diagnostics: Research Contractor and Scientific Advisor, Consulting fee and Research support