Fecal Colonization with Extended-Spectrum Beta-Lactamase and AmpC-Producing Escherichia coli

Background. Extended-spectrum beta-lactamases (ES beta Ls) and AmpC beta-lactamases cause beta-lactam resistance in Escherichia coli. Fecal colonization by ES beta L- and/or AmpC-positive E. coli is a source of nosocomial infections. Methods. In order to investigate inpatient fecal colonization by ES beta Ls and AmpC, antibiotic sensitivity tests were conducted and minimum inhibitory concentrations (MICs) were determined using the disk diffusion method and E-test, respectively. Characterization of ES beta L and AmpC was performed using E-test strips, and a set of PCRs and DNA sequence analyses were used to characterize the ES beta L and AmpC genes. Results. The whole collection of E. coli isolates (n = 50) was sensitive to imipenem, tigecycline, colistin, and fosfomycin, while 26% of the isolates showed reduced susceptibility to ceftazidime (MIC >= 4 mu g/mL). ES beta L was phenotypically identified in 26% (13/50) of cases, while AmpC activity was detected in two ES beta L-producing E. coli isolates. All ES beta L-producing E. coli were positive for the CTX-M gene, eleven isolates carried bla(CTX-M-15), and two isolates carried bla(CTX-M-14) gene. Two CTX-M-positive E. coli isolates carried bla(CMY-2). Conclusions. The alimentary tract is a significant reservoir for ES beta L- and/or AmpC-producing E. coli, which may lead to nosocomial infection.