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Risk Factors for Resistance to Beta-lactam/Beta-lactamase Inhibitors and Carbapenems in Bacteroides spp. Bacteremia

Abstract

Background.   Bacteroides resistant to β-lactam/β-lactamase inhibitors (βL/βLI) and carbapenems are being increasingly recognized but the prevalence and risk factors are unknown. The purpose of this study is to determine the prevalence of Bacteroides resistant to βL/βLIs and carbapenems and identify potential risk factors for the development of resistance to these agents. Methods.  We conducted a single center case-control study of patients with Bacteroides bacteremia from January 1, 2010 to August 31, 2013 at a 1,000-bed tertiary medical center. Cases were defined as patients with Bacteroides bacteremia resistant to carbapenems and/or βL-βLIs. Cases were matched 1:3 to bacteremic patients with susceptible isolates by year of positive blood culture. We determined the prevalence of Bacteroides in the blood resistant or intermediate to βL/βLI and/or carbapenems, risk factors for resistance, and patient outcomes. Cases and controls were compared using Chi square and Wilcoxan rank sum tests. Logistic regression was performed to assess independent predicators of resistance. Results.  159 unique patients with Bacteroides bacteremia were identified. 26 (16%) patients had Bacteroides isolates resistant or intermediate to βL/βLI and/or carbapenems. Amoxicillin/clavulanate was the most common agent to which isolates were resistant or intermediate (11.5%), followed by ertapenem (7.0%) and piperacillin-tazobactam (6.8%). 101 patients were included in the case-control analysis. Duration of therapy with a βL/βLI prior to infection was an independent predictor of resistance (OR 1.25; 95% CI 1.08-2.31). More patients with resistant Bacteroides died prior to discharge (37.5% vs 4.0%; p = <0.001) than patients with susceptible organisms. Conclusion.  We found higher resistance rates among Bacteroides than what has been reported previously. Duration of exposure to βL/βLI was the only independent risk factor for resistance, supporting judicious use of these agents. There was higher mortality with resistant Bacteroides, which is likely confounded by a sicker cohort with a higher percentage in the intensive care unit and longer hospital stay prior to first positive culture. Disclosures.   All authors: No reported disclosures.