Rapid antimicrobial susceptibility testing by VITEK®2 directly from blood cultures in patients with Gram-negative rod bacteremia.

OBJECTIVE: Optimizing therapy for bacteremia is currently limited by the 1-2-day turnaround time required for antimicrobial susceptibility testing (AST). Here, we assess a rapid AST method with VITEK®2 (bioMérieux, France) directly from positive blood cultures.

METHODS: Patient-derived positive blood cultures with Gram-negative rods identified as Enterobacteriaceae and Pseudomonas aeruginosa were prospectively tested, and other blood culture bottles were spiked with carbapenem-resistant Enterobacteriaceae (CRE). Positive cultures were subjected to red blood cell lysis and centrifugation, and setup on VITEK®2.

RESULTS: A total of 109 patient blood cultures and 52 spiked blood cultures were tested. Overall, essential agreement was 97.7% [95% confidence interval (CI) 96.4-99.0], and categorical agreement was 96.8% (95% CI 95.0-98.6). Mean turnaround time from setup to susceptibility results for Enterobacteriaceae in the clinical cultures was 9.0 (±1.3) h.

CONCLUSIONS: Direct susceptibility testing of blood cultures by VITEK®2 for Enterobacteriaceae is an accurate, practical, and inexpensive diagnostic strategy for rapid automated AST.