Recruitment of the OXA-58 carbapenemase in outer membrane vesicles of Acinetobacter baumannii

SÁNCHEZ RI; VIALE AM; CAMERANESI MM; MORAN BARRIO J; LIMANSKY AS

Paraná

Congreso; LIV Reunión Anual SAIB 2018; 2018

SAIB

Acinetobacter baumannii constitutes a worrisome problem in health-care institutions, displaying carbapenem resistance due to the overproduction of OXA-type class-D carbapenemases (CHDLs) (1). Part of this resistance is mediated by the production of outer membrane vesicles (OMV), with postulated roles in cell protection, pathogenicity, and polymicrobial co-infections. However, the detailed mechanisms of OMV production and selection of cargo proteins remains largely unknown. We studied here the biogenesis and secretion of OXA-58 carbapenemase in A. baumannii, using as a model ATCC 17978 (Ab17978) cells transformed with plasmid pOXA-58 which directs high-level expression of the blaOXA-58 gene. OXA-58 production was evaluated by immunoblot and carbapenemase activity in different subcellular fractions of wild-type Ab17978 or ΔcarO mutants lacking the outer membrane protein (OMP) CarO. We found that OXA-58 is a membrane-associated lipoprotein, and that this post-translational modification is essential for its recruitment into OMV since mutant OXA-58 lacking the Cys residue subjected to lipidation was excluded from the OMV. The absence of the OMP CarO in the cells disrupted the selection process of recruitment of OXA-58, allowing the secretion of the non-lipidated carbapenemase. Moreover, CarO also interacts with OmpA, another OMP having pivotal roles in OMV composition. Overall these results indicated that CarO represents an important regulatory component in the selection of proteins recruited for secretion in OMV and in the biogenesis of these entities in A. baumannii.