2159. Accurate Carbapenem Susceptibility Testing Within 5–6 Hours

Abstract

BackgroundPatients infected with multi-drug-resistant (MDR) pathogens may experience long delays to targeted therapies due to the incomplete antimicrobial menus and/or breakpoints tested on current commercial antimicrobial susceptibility testing (AST) systems. Detection of carbapenem resistance poses a challenge to rapid, accurate, minimum inhibitory concentrations (MIC) determinations because some resistant organisms may be inhibited by a carbapenem antibiotic until sufficient carbapenemase production has been achieved and traditional AST platforms must wait to make MIC calls. More accurate carbapenem MICs can be determined by implementing a carbapenemase test alongside rapid AST.MethodsWe demonstrate a novel, proprietary test to detect carbapenemase production that enables rapid MIC testing for carbapenem antibiotics. The test is processed in parallel with the Selux next-generation phenotyping (NGP) AST method, enabling rapid, <6-hour, accurate MIC determinations. The carbapenemase assay utilizes high concentrations of intact bacteria. After 3 hours of incubation, a fluorescent pH indicator is read spectroscopically. The solution pH is lowered by carbapenemase-mediated imipenem degradation and is indicative of enzyme activity.ResultsThis assay accurately identifies carabapenemases across multiple enzyme classes and bacterial species. Figure 1 shows the accuracy and speed of NGP AST at determining MICs for representative isolates from the FDA-CDC antimicrobial resistance bank compared with results from overnight broth microdilution (BMD). To date, over 100 challenge strains of Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii have been tested with no very major errors and an average time-to-result of 5.3 hours.ConclusionBy incorporating a rapid, on-board carbapenemase activity assay, the NGP AST platform rapidly delivers accurate carbapenem results. Combined with NGP’s comprehensive antibiotic menus, this platform will therefore ensure prompt delivery of personalized antibiotic therapies for all patients, including those infected with MDROs, and enable streamlined antibiotic stewardship coordination. Disclosures All authors: No reported disclosures.