c Gram-negative bacteremia is highly fatal, and hospitalizations due to sepsis have been increasing worldwide. Molecular tests that supplement Gram stain results from positive blood cultures provide specific organism information to potentially guide therapy, but more clinical data on their real-world impact are still needed. We retrospectively reviewed cases of Gram-negative bacteremia in hospitalized patients over a 6-month period before (n ‫؍‬ 98) and over a 6-month period after (n ‫؍‬ 97) the implementation of a microarray-based early identification and resistance marker detection system (Verigene BC-GN; Nanosphere) while antimicrobial stewardship practices remained constant. Patient demographics, time to organism identification, time to effective antimicrobial therapy, and other key clinical parameters were compared. The two groups did not differ statistically with regard to comorbid conditions, sources of bacteremia, or numbers of intensive care unit (ICU) admissions, active use of immunosuppressive therapy, neutropenia, or bacteremia due to multidrug-resistant organisms. The BC-GN panel yielded an identification in 87% of Gram-negative cultures and was accurate in 95/97 (98%) of the cases compared to results using conventional culture. Organism identifications were achieved more quickly post-microarray implementation (mean, 10.9 h versus 37.9 h; P < 0.001). Length of ICU stay, 30-day mortality, and mortality associated with multidrug-resistant organisms were significantly lower in the postintervention group (P < 0.05). More rapid implementation of effective therapy was statistically significant for postintervention cases of extended-spectrum beta-lactamase-producing organisms (P ‫؍‬ 0.049) but not overall (P ‫؍‬ 0.12). The Verigene BC-GN assay is a valuable addition for the early identification of Gram-negative organisms that cause bloodstream infections and can significantly impact patient care, particularly when resistance markers are detected. Bloodstream infection remains one of the deadliest and costliest conditions in the United States, more than doubling between 2000 and 2008 and becoming the sixth most common reason for hospitalization (1). Gram-negative bacteremia has become an ever more pressing public health concern, as numbers across the globe continue to rise (2, 3). Although Gram-negative organisms are only responsible for ϳ30% of cases of hospitalacquired infections, they account for 70% of such cases in intensive care units (ICU) in the United States (4). These organisms, including multidrug-resistant (MDR) Pseudomonas aeruginosa and extended-spectrum beta-lactamase (ESBL) or carbapenemresistant Enterobacteriaceae (CRE), are associated with higher mortality rates (1, 3, 4).A timely and appropriate antimicrobial therapy selection is of particular importance. Delays in effective therapy and ineffective empirical therapy are associated with increased patient mortality (4-7). Growing evidence suggests that appropriate, early antibiotic therapy can improve patient outcomes (3,4,6,8). New rapid m...