title: The Acinetobacter Outer Membrane Contains Multiple Specific Channels for Carbapenem β-Lactams as Revealed by Kinetic Characterization Analyses of Imipenem Permeation into Acinetobacter baylyi Cells.
abstract: The number and type of outer membrane (OM) channels responsible for carbapenem uptake inAcinetobacterare still not well defined. Here, we addressed these questions by usingAcinetobacter baylyias a model species and a combination of methodologies aimed to characterize OM channels in their original membrane environment. Kinetic and competition analyses of imipenem (IPM) uptake byA. baylyiwhole cells allowed us to identify different carbapenem-specific OM uptake sites. Comparative analyses of IPM uptake byA. baylyiwild-type (WT) cells and ΔcarOmutants lacking CarO indicated that this OM protein provided a carbapenem uptake site displaying saturable kinetics and common binding sites for basic amino acids compatible with a specific channel. The kinetic analysis uncovered another carbapenem-specific channel displaying a somewhat lower affinity for IPM than that of CarO and, in addition, common binding sites for basic amino acids as determined by competition studies. The use ofA. baylyigene deletion mutants lacking OM proteins proposed to function in carbapenem uptake inAcinetobacter baumanniiindicated that CarO and OprD/OccAB1 mutants displayed low but consistent reductions in susceptibility to different carbapenems, including IPM, meropenem, and ertapenem. These two mutants also showed impaired growth on l-Arg but not on other carbon sources, further supporting a role of CarO and OprD/OccAB1 in basic amino acid and carbapenem uptake. A multiple-carbapenem-channel scenario may provide clues to our understanding of the contribution of OM channel loss or mutation to the carbapenem-resistant phenotype evolved by pathogenic members of theAcinetobactergenus.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina.
authors.forename: Jorgelina
authors.initials: J
authors.lastname: Morán-Barrio
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina.
authors.forename: María M
authors.initials: MM
authors.lastname: Cameranesi
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina.
authors.forename: Verónica
authors.initials: V
authors.lastname: Relling
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina.
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Limansky
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina.
authors.forename: Luciano
authors.initials: L
authors.lastname: Brambilla
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, CONICET, Universidad Nacional de Rosario (UNR), Rosario, Argentina viale@ibr-conicet.gov.ar.
authors.forename: Alejandro M
authors.initials: AM
authors.lastname: Viale
mesh_terms: D000150:Acinetobacter / Q000235:genetics / Q000378:metabolism*; D040981:Acinetobacter baumannii / Q000235:genetics / Q000378:metabolism; D024361:Amino Acids, Basic / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D000077727:Ertapenem; D019143:Evolution, Molecular; D017353:Gene Deletion; D015870:Gene Expression; D015378:Imipenem / Q000378:metabolism*; D007700:Kinetics; D000077731:Meropenem; D018272:Porins / Q000172:deficiency* / Q000235:genetics; D013845:Thienamycins / Q000378:metabolism; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D024361:Amino Acids, Basic; D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D018272:Porins; D013845:Thienamycins; D047090:beta-Lactams; D015378:Imipenem; D000077731:Meropenem; D000077727:Ertapenem
keywords: Acinetobacter; Gram-negative bacteria; antibiotic resistance; basic amino acid channels; carbapenem outer membrane channels; carbapenem resistance; outer membrane proteins