Newly Named Klebsiella aerogenes (formerly Enterobacter aerogenes) Is Associated with Poor Clinical Outcomes Relative to Other <i>Enterobacter</i> Species in Patients with Bloodstream Infection

Abstract

<i>Enterobacter aerogenes</i> was recently renamed <i>Klebsiella aerogenes</i> This study aimed to identify differences in clinical characteristics, outcomes, and bacterial genetics among patients with <i>K. aerogenes</i> versus <i>Enterobacter</i> species bloodstream infections (BSI). We prospectively enrolled patients with <i>K. aerogenes</i> or <i>Enterobacter cloacae</i> complex (<i>Ecc</i>) BSI from 2002 to 2015. We performed whole-genome sequencing (WGS) and pan-genome analysis on all bacteria. Overall, 150 patients with <i>K. aerogenes</i> (46/150 [31%]) or <i>Ecc</i> (104/150 [69%]) BSI were enrolled. The two groups had similar baseline characteristics. Neither total in-hospital mortality (13/46 [28%] versus 22/104 [21%]; <i>P</i> = 0.3) nor attributable in-hospital mortality (9/46 [20%] versus 13/104 [12%]; <i>P</i> = 0.3) differed between patients with <i>K. aerogenes</i> versus <i>Ecc</i> BSI, respectively. However, poor clinical outcome (death before discharge, recurrent BSI, and/or BSI complication) was higher for <i>K. aerogenes</i> than <i>Ecc</i> BSI (32/46 [70%] versus 42/104 [40%]; <i>P</i> = 0.001). In a multivariable regression model, <i>K. aerogenes</i> BSI, relative to <i>Ecc</i> BSI, was predictive of poor clinical outcome (odds ratio 3.3; 95% confidence interval 1.4 to 8.1; <i>P</i> = 0.008). Pan-genome analysis revealed 983 genes in 323 genomic islands unique to <i>K. aerogenes</i> isolates, including putative virulence genes involved in iron acquisition (<i>n</i> = 67), fimbriae/pili/flagella production (<i>n</i> = 117), and metal homeostasis (<i>n</i> = 34). Antibiotic resistance was largely found in <i>Ecc</i> lineage 1, which had a higher rate of multidrug resistant phenotype (23/54 [43%]) relative to all other bacterial isolates (23/96 [24%]; <i>P</i> = 0.03). <i>K. aerogenes</i> BSI was associated with poor clinical outcomes relative to <i>Ecc</i> BSI. Putative virulence factors in <i>K. aerogenes</i> may account for these differences.