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

MORAN BARRIO J; CAMERANESI MM; RELLING V; LIMANSKY AS; BRAMBILLA L; VIALE AM

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2017

0066-4804

The number and type of outer membrane (OM) channels responsible of carbapenem uptake in Acinetobacter are still not well defined. Here, we addressed these questions using Acinetobacter baylyi as 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 by A. baylyi whole cells allowed us to identify different carbapenem-specific OM uptake sites. Comparative analyses of IPM uptake by A. baylyi wild-type (WT) cells and carO mutants 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 somewhat lower affinity for IPM as compared to CarO, and common binding sites also for basic amino acids as judged by competition studies. The use of A. baylyi gene deletion mutants lacking OM proteins proposed to function in carbapenem uptake in A. baumannii indicated that CarO and OprD/OccAB1 mutants displayed low but consistent reductions in the susceptibility to different carbapenems including IPM, meropenem, and ertapenem. These two mutants also showed impaired growth on L-Arg but not in 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 the Acinetobacter genus.