Epidemiology and risk factors for infections due to AmpC β-lactamase-producing Escherichia coli

Objectives: To describe the prevalence and risk factors for infection due to AmpC beta-lactamase-producing Escherichia coli (AmpC-EC). Methods: For the prevalence study, all clinical isolates of E. coli with reduced susceptibility to third-generation cephalosporins were prospectively included from June 2010 to November 2011. For risk factor analysis, a case-control study was conducted. Cases were patients with an infection due to AmpC-EC. Controls were patients infected with cephalosporin-susceptible E. coli, matched 1: 2. Detection of bla(AmpC) genes was done with a multiplex AmpC-PCR, and hyperproduction of E. coli chromosomal bla(AmpC) by quantitative RT-PCR. Alteration of the bla(AmpC) promoter was studied by PCR and sequencing. Results: We identified 243 (1.1%) AmpC-EC strains out of 21563 clinical isolates. Three cases with strains carrying ESBLs, 18 strains that were considered due to colonization and 8 cases lost to clinical follow-up were excluded. Finally, 214 cases were included in the analysis. Ninety-one cases (42.5%) and 269 (62.8%) controls were strictly community acquired (P<0.001). Thirty-five (16.3%) cases and 186 controls (43.5%) did not have any identifiable risk factor (P<0.001). Among cases, 158 (73.8%) were found to harbour an acquired AmpC (73.4% CMY-2). Previous use of fluoroquinolones [OR 2.6 (95% CI 1.12-3.36); P = 0.008] was independently associated with AmpC-EC in the multivariate analysis. Conclusions: Prevalence of AmpC in E. coli remains low in our area. Plasmid acquisition (CMY type) represents the main mechanism of AmpC production. A high proportion of community-acquired isolates and patients with no identifiable risk factors were found. Previous use of fluoroquinolones was identified as a risk factor.