Fecal Colonization with Extended-Spectrum Beta-Lactamase and AmpC-ProducingEscherichia coli

Abstract

Background. Extended-spectrumβ-lactamases (ESβLs) and AmpCβ-lactamases causeβ-lactam resistance inEscherichia coli. Fecal colonization by ESβL- and/or AmpC-positiveE. coliis a source of nosocomial infections.Methods. In order to investigate inpatient fecal colonization by ESβLs and AmpC, antibiotic sensitivity tests were conducted and minimum inhibitory concentrations (MICs) were determined using the disk diffusion method andE-test, respectively. Characterization of ESβL and AmpC was performed usingE-test strips, and a set of PCRs and DNA sequence analyses were used to characterize the ESβL and AmpC genes.Results. The whole collection ofE. coliisolates (n=50) was sensitive to imipenem, tigecycline, colistin, and fosfomycin, while 26% of the isolates showed reduced susceptibility to ceftazidime (MIC ≥ 4 μg/mL). ESβL was phenotypically identified in 26% (13/50) of cases, while AmpC activity was detected in two ESβL-producingE. coliisolates. All ESβL-producingE. coliwere positive for the CTX-M gene, eleven isolates carriedblaCTX-M-15, and two isolates carriedblaCTX-M-14gene. Two CTX-M-positiveE. coliisolates carriedblaCMY-2.Conclusions. The alimentary tract is a significant reservoir for ESβL- and/or AmpC-producingE. coli, which may lead to nosocomial infection.