title: Phenotypic screening of carbapenemases and associated β-lactamases in carbapenem-resistant Enterobacteriaceae.
abstract: Dissemination of carbapenem resistance among Enterobacteriaceae poses a considerable threat to public health. Carbapenemase gene detection by molecular methods is the gold standard but is available in only a few laboratories. The aim of this study was to test phenotypic methods for the detection of metallo-β-lactamase (MBL)- or Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae and associated mechanisms of β-lactam resistance against a panel of 30 genotypically characterized carbapenem-resistant Enterobacteriaceae : 9 MBL, 7 KPC, 6 OXA-48, and 8 extended-spectrum β-lactamase (ESBL) or AmpC β-lactamases associated with decreased permeability. We used carbapenemase inhibitor-impregnated agar to test for carbapenem-resistant strains. Differences in the inhibition zone sizes of the meropenem, imipenem, ertapenem, and doripenem disks were measured between control and inhibitor (EDTA or phenylboronic acid [PBA] with or without cloxacillin)-impregnated Mueller-Hinton agar with a cutoff of 10 mm. All 9 MBL- and 7 KPC-producing Enterobacteriaceae were identified from the differences in zone size in the presence and absence of specific inhibitors, regardless of the carbapenem MICs and including isolates with low-level resistance to carbapenems. We also detected their associated β-lactam resistance mechanisms (11 ESBL-type and 5 class A β-lactamase 2b). No differences in zone size were observed for OXA-48-producing strains or other carbapenem resistance mechanisms such as ESBL and decreased permeability. We propose a new strategy to detect carbapenemases (MBL- and KPC-type) and associated mechanisms of β-lactam resistance (ESBL or class A β-lactamase 2b) by the use of inhibitor-impregnated agar. A rapid phenotypic detection of resistance mechanisms is important for epidemiological purposes and for limiting the spread of resistant strains by implementing specific infection control measures.
authors.affiliation: Laboratoire de Microbiologie, Hôpital Robert Debré, Assistance Publique des Hôpitaux de Paris, Paris, France.
authors.forename: André
authors.initials: A
authors.lastname: Birgy
authors.forename: Philippe
authors.initials: P
authors.lastname: Bidet
authors.forename: Nathalie
authors.initials: N
authors.lastname: Genel
authors.forename: Catherine
authors.initials: C
authors.lastname: Doit
authors.forename: Dominique
authors.initials: D
authors.lastname: Decré
authors.forename: Guillaume
authors.initials: G
authors.lastname: Arlet
authors.forename: Edouard
authors.initials: E
authors.lastname: Bingen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D015780:Carbapenems / Q000494:pharmacology*; D052978:Disk Diffusion Antimicrobial Tests; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D010641:Phenotype; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015780:Carbapenems; D001618:beta-Lactamases; C063912:carbapenemase