title: Acquisition of Carbapenem Resistance by Plasmid-Encoded-AmpC-Expressing Escherichia coli.
abstract: Although AmpC β-lactamases can barely degrade carbapenems, if at all, they can sequester them and prevent them from reaching their targets. Thus, carbapenem resistance in Escherichia coli and other Enterobacteriaceae can result from AmpC production and simultaneous reduction of antibiotic influx into the periplasm by mutations in the porin genes. Here we investigated the route and genetic mechanisms of acquisition of carbapenem resistance in a clinical E. coli isolate carrying blaCMY-2on a plasmid by selecting for mutants that are resistant to increasing concentrations of meropenem. In the first step, the expression of OmpC, the only porin produced in the strain under laboratory conditions, was lost, leading to reduced susceptibility to meropenem. In the second step, the expression of the CMY-2 β-lactamase was upregulated, leading to resistance to meropenem. The loss of OmpC was due to the insertion of an IS1 element into the ompC gene or to frameshift mutations and premature stop codons in this gene. The blaCMY-2gene was found to be located on an IncIγ plasmid, and overproduction of the CMY-2 enzyme resulted from an increased plasmid copy number due to a nucleotide substitution in the inc gene. The clinical relevance of these genetic mechanisms became evident from the analysis of previously isolated carbapenem-resistant clinical isolates, which appeared to carry similar mutations.
authors: Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, Utrecht, Netherlands.
authors: Ria
authors: R
authors: van Boxtel
authors: Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center Rotterdam, Rotterdam, Netherlands.
authors: Agnes A
authors: AA
authors: Wattel
authors: Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, Utrecht, Netherlands.
authors: Jesús
authors: J
authors: Arenas
authors: Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center Rotterdam, Rotterdam, Netherlands.
authors: Wil H F
authors: WH
authors: Goessens
authors: Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, Utrecht, Netherlands j.p.m.tommassen@uu.nl.
authors: Jan
authors: J
authors: Tommassen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015780:Carbapenems / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D018272:Porins / Q000235:genetics / Q000378:metabolism; D013845:Thienamycins / Q000494:pharmacology; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015780:Carbapenems; D029968:Escherichia coli Proteins; D018272:Porins; D013845:Thienamycins; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; D000077731:Meropenem
keywords: AmpC; CMY-2; Escherichia coli; carbapenem resistance; plasmid-mediated resistance; porins