Rapid detection of gram-negative antimicrobial resistance determinants directly from positive blood culture broths using a multiplex PCR system.

Abstract

Currently available rapid blood culture diagnostics detect few gram-negative resistance determinants, limiting their clinical utility. We prospectively evaluated the prototype BIOFIRE FILMARRAY Antimicrobial Resistance (AMR) Panel, a rapid multiplex PCR test that detects 31 AMR genes, on residual positive blood culture broths from patients with gram-negative bacteremia due to five target organisms at a New York City hospital. Predicted antimicrobial resistance based on the AMR Panel was compared to results from broth microdilution testing of bloodstream isolates recovered in culture. A simulated stewardship study assessed opportunities for the optimization of therapy if the AMR Panel results had been available for patient care in real time. We enrolled 148 patients with gram-negative bacteremia (Escherichia coli, n = 75; Klebsiella pneumoniae, n = 44; Pseudomonas aeruginosa, n = 17; Enterobacter cloacae complex, n = 9; and Acinetobacter baumannii, n = 3). The sensitivity of the AMR Panel for predicting antimicrobial resistance was ≥90% for 10/14 antimicrobial agents in E. coli and for 10/16 agents in K. pneumoniae. Specificity was ≥90% for 15/17 agents in E. coli and for all 16 agents in K. pneumoniae. Performance for other organisms was poor. For E. coli or K. pneumoniae bacteremia, use of the AMR Panel could have led to earlier escalation or de-escalation of β-lactam therapy in a majority of patients compared to what actually occurred. This study demonstrates that a rapid multiplex PCR test with a large menu of AMR genes can be applied to positive blood culture broths to rapidly predict resistance to frontline antimicrobial agents in patients with E. coli or K. pneumoniae bacteremia.IMPORTANCEPatients with gram-negative bacteremia require urgent treatment with antimicrobial agents that are effective against their infecting pathogen. However, conventional laboratory work-up of blood cultures takes days to yield results, and during this time, patients may receive ineffective therapies. We evaluated the prototype BIOFIRE FILMARRAY AMR Panel, an assay that detects 31 genes in gram-negative bacteria that confer resistance to β-lactams, fluoroquinolones, and aminoglycosides in approximately 1 hour, directly from positive blood culture broths, and compared these results to antimicrobial susceptibility testing of isolates recovered in culture. We found that the AMR Panel accurately predicted resistance in Escherichia coli and Klebsiella pneumoniae to most antimicrobials. Moreover, if results from this assay had been used for patient care, there would have been opportunities to optimize antimicrobial prescribing more quickly than using conventional methods. These data demonstrate how novel molecular assays could optimize care for patients with E. coli and K. pneumoniae bacteremia.