Methods: Starting in August 2017, patients with blood cultures positive for Gram-negative rods were prospectively included. In addition, aerobic and anaerobic blood culture bottles were spiked with a standardized inoculum of enteric Gram-negative rods from a repository of frozen samples. Positive blood cultures were processed using a newly-developed protocol based on red blood cell lysis and differential centrifugation of bacteria, followed by VITEK®2 card set-up. VITEK®2 results from the direct method were compared to a reference method (VITEK®2 results using a 24-hour colony).
Results: In the prospective study, a total of 109 non-duplicate samples were collected, with E. coli (n=54) and Klebsiella pneumoniae (n=51) the main pathogens detected. In addition, a total of 52 blood culture bottles were spiked with resistant Gram-negative rods. Overall weighted essential agreement was 98.8%, and categorical agreement was 97.9% between the direct and reference methods. Accurate results were produced for the main antibiotics used to treat enteric Gram-negative bacteremia, including ceftriaxone, piperacillin-tazobactam and meropenem. Mean turnaround time to susceptibility results for Enterobacteriaceae in the prospective study was 9.0 (±1.3) hours.
Conclusion: Preliminary data from direct antimicrobial susceptibility testing by VITEK®2 for enteric Gram-negative rod bacteremia suggest this technique is accurate, practical, easily integrated in the laboratory workflow, and substantially cheaper than its competitor technology. The next phase of this study will assess the impact of faster antimicrobial susceptibility turnaround time on patient outcomes and antimicrobial stewardship targets.
N. Watz, None
N. Banaei, None