Bloodstream infections caused by Escherichia coli producing AmpC β-lactamases: epidemiology and clinical features.

The aim of the study was to investigate the epidemiology and clinical features of bloodstream infections due to Escherichia coli producing AmpC β-lactamases (AmpC-Ec-BSI). In a multi-centre case-control study, all third-generation-cephalosporin-resistant Escherichia coli BSI (3GC-Ec-BSI) isolates were analysed. Acquired bla AmpC (bla ac-AmpC ) detection was done by polymerase chain reaction (PCR) and sequencing. Chromosomal bla AmpC (bla c-AmpC ) expression was quantified by real-time PCR. Cases were patients with AmpC-Ec-BSI. Controls were patients with cephalosporin-susceptible E. coli BSI, matched 1:1 by sex and age. Demographics, comorbidities, intrinsic and extrinsic risk factors for antimicrobial resistance, clinical presentation and outcomes were investigated. Among 841 E. coli BSI, 17 were caused by AmpC-Ec (2 %). Eleven isolates (58.8 %) had bla ac-AmpC and six were bla c-AmpC overproducers. The mean age of cases was 66.2 years and 71 % were men. Cases were more frequently healthcare-related (82 vs. 52 % controls, p < 0.05) and presented more intrinsic and extrinsic risk factors. At least one risk factor was present in 94.1 % of cases vs. 41.7 % of controls (p = 0.002). Severity and length of stay (LOS) were higher among cases (mean Pitt Score 2.6 vs. 0.38 in controls, p = 0.03; LOS 17.5 days vs. 6 in controls, p = 0.02). Inappropriate empirical therapy (IET) was administered to 70.6 % of cases and 23.5 % of controls (p < 0.003). No differences were found in terms of cure rate at the 14th day and mortality. Bloodstream infections due to AmpC-Ec (mostly plasmid-mediated) are infrequent in our area. AmpC-Ec-BSI affects mainly patients with intrinsic risk factors and those with previous antibiotic exposure. A high proportion received IET.