In vitro study of virulence potential of Acinetobacter baumannii outer membrane vesicles

Acinetobacter baumannii has emerged as an important opportunistic pathogen mostly causing nosocomial infections. The virulence factors of this important pathogen are largely unknown. Outer membrane vesicles (OMV) are naturally secreted by many gram negative and gram positive bacteria. These vesicles contain outer membrane proteins, lipids, periplasmic proteins, DNA and RNA. Their role in intracellular and intercellular signaling, transfer of virulence factors and eliciting immune response in host cells has been established in many pathogens. In this study, we investigated OMVs from three multi-drug resistant (MDR) clinical isolates and a non-MDR reference strain of A. baumannii for virulence potential. A. baumannii OMVs showed phospholipase C, hemolytic and leukotoxic activities. We found large variations in virulence potential between OMVs of MDR clinical isolates and non-MDR reference strain. These effector molecules were concentrated in OMVs than whole cell bacterial culture and cell-free supernatant. OMV-mediated phospholipase, hemolytic and leucotoxic activities may have a key role in pathogenicity of A. baumannii infection and may be future targets for therapeutic and preventive strategies. This is, to the best of our knowledge, the first report showing virulence potential of A. baumannii OMVs.