Vaccination with outer membrane vesicles from Francisella noatunensis reduces development of francisellosis in a zebrafish model

Abstract

Infection of fish with the facultative intracellular bacterium Francisella noatunensis remains an unresolved problem for aquaculture industry worldwide as it is difficult to vaccinate against without using live attenuated vaccines. Outer membrane vesicles (OMVs) are biological structures shed by Gram-negative bacteria in response to various environmental stimuli. OMVs have successfully been used to vaccinate against both intracellular and extracellular pathogens, due to an ability to stimulate innate, cell-mediated and humoral immune responses. We show by using atomic force and electron microscopy that the fish pathogenic bacterium F. noatunensis subspecies noatunensis (F.n.n.) shed OMVs both in vitro into culture medium and in vivo in a zebrafish infection model. The main protein constituents of the OMV are IglC, PdpD and PdpA, all known Francisella virulence factors, in addition to the outer membrane protein FopA and the chaperonin GroEL, as analyzed by mass spectrometry. The vesicles, when used as a vaccine, reduced proliferation of the bacterium and protected zebrafish when subsequently challenged with a high dose of F.n.n. without causing adverse effects for the host. Also granulomatous responses were reduced in F.n.n.-challenged zebrafish after OMV vaccination. Taken together, the data support the possible use of OMVs as vaccines against francisellosis in fish.

Larva of greater wax moth Galleria mellonella is a suitable alternative host for the fish pathogen Francisella noatunensis subsp. orientalis

“…Moreover, the detection of lethal activity in sterile culture filtrates in this present study suggests the presence of extracellular virulence factors, such as toxins or degradative enzymes, and fish-pathogenic Francisella spp. do produce outer-membrane vesicles embedded with virulence factors [45,58]. Beyond virulence factor discovery and probing of host-pathogen interactions, the G. mellonella system would be useful for Fig.…”

Dissection of Francisella-Host Cell Interactions in Dictyostelium discoideum

“…Expression of iglC is highly upregulated during intracellular growth (38), and intriguingly, IglC is the most abundant protein identified in outer-membrane vesicles (OMVs) secreted by F. noatunensis subsp. noatunensis (39).…”

Larva of greater wax moth Galleria mellonella is a suitable alternative host for the fish pathogen Francisella noatunensis subsp. orientalis

“…Moreover, the detection of lethal activity in sterile culture filtrates in this present study suggests the presence of extracellular virulence factors, such as toxins or degradative enzymes, and fish-pathogenic Francisella spp. do produce outer-membrane vesicles embedded with virulence factors [45,58]. Beyond virulence factor discovery and probing of host-pathogen interactions, the G. mellonella system would be useful for determining the relative virulence of isolates, as such information is useful for identifying particularly problematic (i.e., virulent) strains.…”