Abstract
BackgroundEnterobacter spp. possess chromosomal AmpC beta-lactamases that may be expressed at high levels. Previous studies have demonstrated a risk of relapsed bacteraemia following therapy with third generation cephalosporins (3GCs). What additional factors predict microbiological failure in Enterobacter bacteraemia is unclear. We aimed to determine factors associated with microbiological failure in Enterobacter bacteraemia.MethodsWe retrospectively identified cases of bacteraemia caused by Enterobacter spp. occurring in four hospitals. Using a case–control design, we determined clinical risk factors for persistence or relapse defined as repeated positive blood cultures collected between 72 hours and up to 28 days post initial positive blood culture.ResultsDuring the study period a total of 922 bacteraemia events caused by Enterobacter spp. in adults were identified. The overall risk of relapsed or persisting bacteraemia at 28 days was low (31 of 922, 3.4%), with only 2 patients experiencing emergent resistance to 3GCs. A total of 159 patients were included in the case–control study. Using multivariate logistic regression, independent predictors for relapse were a line-associated source of infection (OR 3.87; 95% CI 1.56-9.60, p = 0.004) and the presence of immunosuppression (OR 2.70; 95% CI 1.14-6.44, p = 0.02). On univariate analysis definitive therapy with a broad-spectrum beta-lactam-beta-lactamase inhibitor (BLBLI, e.g. piperacillin-tazobactam) was not associated with relapse (OR 1.83; 95% CI 0.64-5.21, p = 0.26) although the proportion of patients receiving a BLBLI as definitive therapy was relatively small (21/159, 13.2%).ConclusionsThe risk of relapsed or persistent Enterobacter bacteraemia appears to be low in Australia. A line-associated source of infection and immunocompromise were significant independent predictors for relapse. Larger, preferably randomized, studies are needed to address whether BLBLIs represent an effective carbapenem-sparing option for Enterobacter bacteraemia.
Highlights
Enterobacter spp. possess chromosomal AmpC beta-lactamases that may be expressed at high levels
During the study periods for each location, a total of 922 positive blood cultures growing Enterobacter spp. were identified, after excluding polymicrobial infections, individuals aged
In a cohort of patients with bacteraemia caused by Enterobacter species, the overall risk of relapsed bacteraemia was low
Summary
Enterobacter spp. possess chromosomal AmpC beta-lactamases that may be expressed at high levels. Bacteria belonging to the genus Enterobacter spp. are Gram-negative Proteobacteria of the family Enterobacteriaceae and currently comprise 22 species [1] They represent a diverse group which are widely distributed in nature [2] and possess multiple mechanisms to allow survival in a variety of environmental niches [3]. The annual incidence of bacteraemia caused by Enterobacter spp. has been reportedly increasing in some parts of the world [6] This bacterial genus presents particular challenges for the selection of optimal therapy due to the presence of chromosomally encoded AmpC beta-lactamase enzymes [7]. [2] Such variants are usually present at low levels (e.g. between 10−5 to 10−7 of the total bacterial population) but may be rapidly selected during antibiotic therapy [2] This phenomenon has been best described with the use of third generation cephalosporins (3GCs).
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