Membrane Vesicles Derived from Bordetella bronchiseptica: Active Constituent of a New Vaccine against Infections Caused by This Pathogen (2017)

<i>Bordetella bronchiseptica</i>, a Gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including humans (albeit rarely). We recently designed <i>Bordetella pertussis</i> and <i>Bordetella parapertussis</i> experimental vaccines based on outer membrane vesicles (OMVs) derived from each pathogen, and we obtained protection against the respective infections in mice. Here, we demonstrated that OMVs derived from virulent-phase <i>B. bronchiseptica</i> (OMVBbvir<sup>+</sup>) protected mice against sublethal infections with different <i>B. bronchiseptica</i> strains, two isolated from farm animals and one isolated from a human patient. In all infections, we observed that the <i>B. bronchiseptica</i> loads were significantly reduced in the lungs of vaccinated animals; the lung-recovered CFU were decreased by ≥4 log units, compared with those detected in the lungs of nonimmunized animals (<i>P</i> < 0.001). In the OMVBbvir<sup>+</sup>-immunized mice, we detected IgG antibody titers against <i>B. bronchiseptica</i> whole-cell lysates, along with an immune serum having bacterial killing activity that both recognized <i>B. bronchiseptica</i> lipopolysaccharides and polypeptides such as GroEL and outer membrane protein C (OMPc) and demonstrated an essential protective capacity against <i>B. bronchiseptica</i> infection, as detected by passive <i>in vivo</i> transfer experiments. Stimulation of cultured splenocytes from immunized mice with OMVBbvir<sup>+</sup> resulted in interleukin 5 (IL-5), gamma interferon (IFN-γ), and IL-17 production, indicating that the vesicles induced mixed Th2, Th1, and Th17 T-cell immune responses. We detected, by adoptive transfer assays, that spleen cells from OMVBbvir<sup>+</sup>-immunized mice also contributed to the observed protection against <i>B. bronchiseptica</i> infection. OMVs from avirulent-phase <i>B. bronchiseptica</i> and the resulting induced immune sera were also able to protect mice against <i>B. bronchiseptica</i> infection.<b>IMPORTANCE</b><i>Bordetella bronchiseptica</i>, a Gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including humans (albeit rarely). Several vaccines aimed at preventing <i>B. bronchiseptica</i> infection have been developed and used, but a safe effective vaccine is still needed. The significance and relevance of our research lie in the characterization of the OMVs derived from <i>B. bronchiseptica</i> as the source of a new experimental vaccine. We demonstrated here that our formulation based on OMVs derived from virulent-phase <i>B. bronchiseptica</i> (OMVBbvir<sup>+</sup>) was effective against infections caused by <i>B. bronchiseptica</i> isolates obtained from different hosts (farm animals and a human patient). <i>In vitro</i> and <i>in vivo</i> characterization of humoral and cellular immune responses induced by the OMVBbvir<sup>+</sup> vaccine enabled a better understanding of the mechanism of protection necessary to control <i>B. bronchiseptica</i> infection. Here we also demonstrated that OMVs derived from <i>B. bronchiseptica</i> in the avirulent phase and the corresponding induced humoral immune response were able to protect mice from <i>B. bronchiseptica</i> infection. This realization provides the basis for the development of novel vaccines not only against the acute stages of the disease but also against stages of the disease or the infectious cycle in which avirulence factors could play a role.