Prevalence of AmpC β-lactamase in Clinical Isolates of Escherichia coli, Klebsiella spp., and Proteus mirabilis in a Tertiary Hospital in Tehran, Iran
Background: AmpC β-lactamase confers resistance to a variety of β-lactam agents, and all plasmid-mediated AmpC genes are considered clinically significant. The transfer of the AmpC gene to plasmid has resulted in dissemination among the Enterobacteriaceaefamily, including Escherichia coli, Klebsiella spp., and Proteus mirabilis.Objectives: The prevalence of plasmid-mediated AmpC genes was determined in isolates of E. coli, Klebsiella spp., and P. mirabiliswith reduced susceptibility to cefoxitin or extended-spectrum cephalosporins by the multiplex PCR method.Methods: A total of 310 consecutive non-duplicate isolates of E. coli, Klebsiella spp., and P. mirabilis were obtained from various clinical specimens. Isolates with positive screening test results were subjected to further molecular evaluation.Results: Fifty isolates were positive on the screening test. Among them, positive PCR reactions were identified in 35/221 and 12/77 isolates of E. coli and Klebsiella spp., respectively, including 16 (34.0%) for CIT only, 7 (14.8%) for DHA only, and 24 (51.0%) for both DHA and CIT. No isolate was positive for FOX or MOX. No Proteus organism was positive for AmpC genes.Conclusions: Currently, phenotypic tests are unable to accurately and reliably recognize plasmid-mediated AmpC β-lactamase-producing organisms. Although not possible for routine testing, clinical laboratories, especially in referral centers, should employ molecular testing for surveillance studies.