221. Newly-Named Klebsiella aerogenes Is Associated with Poor Clinical Outcomes Relative to Enterobacter cloacae Complex in Patients with Bloodstream Infection

BACKGROUND: Whole-genome-based comparative bacterial phylogenetics led to Enterobacter aerogenes being renamed Klebsiella aerogenes. It is unclear how infections with K. aerogenes differ from Enterobacter cloacae complex (Ecc) regarding clinical characteristics, antibiotic resistance, patient outcomes, and bacterial virulence genes. METHODS: Adult inpatients with K. aerogenes or Ecc bloodstream infection (BSI) were prospectively enrolled at Duke from 2002–2015. Whole-genome bacteria sequencing was performed. Chi-squared, Fisher’s exact, Mann–Whitney U, t-tests, and multivariable logistic regression models identified risk factors for infection and clinical outcomes. PanOCT algorithm identified flexible genomic islands (fgi). Multidrug resistance (MDR) was defined as resistance to ≥3 drug classes and poor clinical outcome as death before discharge and/or BSI complication (septic shock, acute kidney injury, acute lung injury/acute respiratory distress syndrome, disseminated intravascular coagulation). RESULTS: We identified 104 (69%) patients with Ecc BSI and 46 (31%) with K. aerogenes BSI (N = 150). Patients with Ecc BSI more often required hemodialysis (23% vs. 9%, P = 0.04). MDR was similar between Ecc and K. aerogenes (30% vs. 33%; P = 0.85). Total (21% vs. 28%; P = 0.3) and attributable in-hospital mortality (12% vs. 20%; P = 0.3) did not differ between the two genera. Poor clinical outcome was more common with K. aerogenes BSI (70% vs. 40%, P = 0.001) and remained significant after adjusting for age, source of BSI, site of acquisition (e.g., hospital), days to appropriate antibiotic, and chronic APACHE-II score (odds ratio 2.8, 95% CI 1.2–6.4, P = 0.001). Ecc and K. aerogenes isolates formed 14 and 3 phylogenetic clades, respectively (Fig 1A). K. aerogenes contained 983 core genes, grouped within 324 fgi, that were not present in Ecc (Fig 1B). These included homologs to virulence genes involved in iron acquisition, flagella synthesis, and fimbriae production. CONCLUSION: Patients with BSI due to K. aerogenes had poor clinical outcomes relative to Ecc. Multiple unique K. aerogenes genes homologous to virulence factors may contribute to this difference. [Image: see text] DISCLOSURES: All authors: No reported disclosures.