Background: Knowledge of the clinical features of infections caused by Escherichia coli strains that produce plasmid-mediated AmpC beta-lactamase is limited. Of the several groups of plasmid-mediated AmpC beta-lactamases, CMY-type beta-lactamase is the most common in the United States.
Methods: We prospectively identified patients infected or colonized with E. coli strains that produce CMY-type beta-lactamase, and we collected clinical data over a 7-month period. A retrospective cohort study was performed to identify features associated with these cases. Patients with extended-spectrum beta-lactamase-producing E. coli were used as a control group. Pulsed-field gel electrophoresis, plasmid analysis, and phylogenetic typing were performed.
Results: Twenty-two patients with infection or colonization due to CMY-type beta-lactamase-producing E. coli and 25 patients with infection or colonization due to extended-spectrum beta-lactamase-producing E. coli were identified. The demographic characteristics of the patients were similar in both cohorts. Patients with CMY-type beta-lactamase-producing E. coli were significantly more likely to have symptomatic infection than were patients with extended-spectrum beta-lactamase-producing E. coli (P = .028). The CMY-type beta-lactamase was identified as CMY-2 or its variants. Ninety-four percent of the CMY-type beta-lactamase-producing isolates belonged to E. coli phylogenetic groups B2 and D, which are associated with virulence. Many of the isolates shared similar plasmid profiles, whereas the pulsed-field gel electrophoresis profiles were diverse. Co-resistance to non-beta-lactam antimicrobials was common.
Conclusion: In Pittsburgh, Pennsylvania, CMY-type beta-lactamase-producing E. coli strains are almost as common as extended-spectrum beta-lactamase-producing E. coli strains, and they cause symptomatic infection in the majority of cases.