1051. Increased Mortality in Bacteremia by Enterobacter Species With Discordant Imipenem and Ertapenem Susceptibilities

BACKGROUND: Carbapenem-resistant Enterobacteriaceae (CRE) that are resistant only to one carbapenem have been reported, but the frequency of discordance between ertapenem and imipenem/meropenem is not known for Enterobacter species. We investigated the occurrence of discordant carbapenem susceptibilities in Enterobacter species bacteremia and the potential association with increased mortality. METHODS: We examined all cases of Enterobacter species bacteremia from January 2012 to December 2016 at the Michael E. DeBakey VA Medical Center in Houston, Texas, USA. Clinical and microbiological data were independently extracted by two investigators. Antibiotic susceptibility testing results were interpreted according to current CLSI breakpoints. RESULTS: We found 14/67 (20.9%) isolates had discordance between ertapenem and imipenem susceptibilities. Eight isolates were ertapenem susceptible/imipenem nonsusceptible and six isolates were ertapenem nonsusceptible/imipenem susceptible (table). Bacteremia cleared in 94.5% (52/55) of all patients who had follow-up cultures, including infection by all (13/13) isolates with discordant carbapenem susceptibilities tested. Thirty-day mortality was statistically higher in infection by isolates with discordant carbapenem susceptibilities than by isolates that were susceptible to all tested carbapenems (10% vs. 36%; P = 0.03, Fisher’s exact test). In-hospital mortality was also higher in the discordant cohort as well (12% vs. 36%; P = 0.04, Fisher’s exact test). Acute severity of illness at bacteremia onset did not differ between the groups (median Pitt bacteremia score 2 vs. 3; P = 0.11, Wilcoxon rank-sum test). CONCLUSION: Bacteremia by Enterobacter species with discordant ertapenem and imipenem/meropenem susceptibilities is a relevant clinical issue, occurring in 20.9% of Enterobacter species bacteremias at our institution, and the discordance is associated with increased mortality. Whether such species can be safely treated with one carbapenem but not another is worth further investigation. MIC: minimum inhibitory concentration; S: susceptible; I: intermediate; R: resistant; DISCLOSURES: B. W. Trautner, Paratek: Consultant, Consulting fee. Zambon: Consultant, Consulting fee and Research grant.