Performance of the Accelerate Pheno™ system for identification and antimicrobial susceptibility testing of a panel of multidrug-resistant Gram-negative bacilli directly from positive blood cultures.

Objectives: To evaluate the performance of the Accelerate Pheno™ system for the identification and antimicrobial susceptibility testing (AST) of a panel of Gram-negative bacilli (GNB) with different resistance profiles (e.g. penicillinases, ESBLs, cephalosporinase overproduction, carbapenemases, impermeability) directly from positive blood cultures in <7 h.

Methods: A panel of 105 clinical strains previously characterized for the presence of β-lactamase-encoding genes was tested. Approximately 100 cfu of each isolate was inoculated into sterile blood culture bottles and incubated in a BD BACTEC™ FX automated system (Becton Dickinson, USA). Positive blood cultures were subjected to parallel testing using the Accelerate Pheno™ system and conventional culture methods [identification of isolated colonies by MALDI-TOF and VITEK® 2 system (bioMérieux, France), and AST by disc diffusion and Etest following EUCAST recommendations].

Results: The overall identification agreement between the Accelerate Pheno™ system and conventional culture methods was 100% (105/105). The overall categorical agreement between the system and culture-based AST was 94.9% (1169/1232), with rates for minor errors of 4.1% (51/1232), major errors 0.3% (4/1232) and very major errors 0.7% (8/1232). The Accelerate Pheno™ system produced AST results indicative of third-generation cephalosporinases (26/26) and carbapenem-resistant strains (52/55).

Conclusions: The Accelerate Pheno™ system is an accurate, sensitive and easy-to-use test for the rapid identification and AST of MDR GNB in bloodstream infections. Given the burden of multidrug resistance, its implementation in the microbiology laboratory could be a useful tool for prompt management of sepsis.