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

• Published in: Fish & shellfish immunology Vol. 42; no. 1; pp. 50 - 57
• Main Authors: Brudal, Espen, Lampe, Elisabeth O., Reubsaet, Léon, Roos, Norbert, Hegna, Ida K., Thrane, Ida Marie, Koppang, Erling O., Winther-Larsen, Hanne C.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2015
• Subjects: Animals; Bacterial Outer Membrane Proteins - immunology; Bacterial Vaccines - pharmacology; Chromatography, Liquid; Danio rerio; Electrophoresis, Polyacrylamide Gel; Francisella; Francisella - immunology; Francisella - ultrastructure; Freshwater; Gram-Negative Bacterial Infections - prevention & control; Immunity, Humoral - drug effects; Immunity, Humoral - immunology; Kaplan-Meier Estimate; Microscopy, Atomic Force; Microscopy, Electron, Transmission; Outer membrane vesicles; Tandem Mass Spectrometry; Transport Vesicles - immunology; Transport Vesicles - ultrastructure; Vaccination - methods; Vaccine; Zebrafish; LAV; Outer membrane vesicles; Zebrafish; Vaccine; CFU; Francisella; F.n.n; d.p.i; F.n.o; w.p.i; qPCR; F.t.n; OMVs; GE; gDNA
• ISSN: 1050-4648; 1095-9947
• DOI: 10.1016/j.fsi.2014.10.025

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. •Isolation of Outer membrane vesicles from Francisella noatunensis.•Establishment of an adult zebrafish infection model for F. noatunensis ssp. noatunensis.•Outer membrane vesicles protect fish against francisellosis.