Characterization and Vaccine Potential of Outer Membrane Vesicles from Photobacterium damselae subsp. piscicida

Abstract

Photobacterium damselae subsp. piscicida (Phdp) is a Gram-negative fish pathogen with worldwide distribution and broad host specificity that causes heavy economic losses in aquaculture. Although Phdp was first identified more than 50 years ago, its pathogenicity mechanisms are not completely understood. In this work, we report that Phdp secretes large amounts of outer membrane vesicles (OMVs) when cultured in vitro and during in vivo infection. These OMVs were morphologically characterized and the most abundant vesicle-associated proteins were identified. We also demonstrate that Phdp OMVs protect Phdp cells from the bactericidal activity of fish antimicrobial peptides, suggesting that secretion of OMVs is part of the strategy used by Phdp to evade host defense mechanisms. Importantly, the vaccination of sea bass (Dicentrarchus labrax) with adjuvant-free crude OMVs induced the production of anti-Phdp antibodies and resulted in partial protection against Phdp infection. These findings reveal new aspects of Phdp biology and may provide a basis for developing new vaccines against this pathogen.

Marine Delivery Vehicles: Molecular Components and Applications of Bacterial Extracellular Vesicles

“…To be sure that a bacterium produces membrane vesicles methods for their visualization are necessary (Figure 2). The large majority of marine BEVs have been visualised by negative stained TEM (Transmission Electron Microscopy) [37,40,47,57,77,78,[101][102][103][104][105][106]] SEM (Scansion Electron Microscopy), epifluorescence microscopy, Atomic Force Microscopy (AFM). FE-SEM (Field Emission-Scanning Electron Microscopy) analysis has been used for Shevanella vesiculosa HM13 for observing the surface morphology of the cells secreting BEVs thus demonstrating the absence of cell lysis while producing vesicles [47].…”