The Pasteurallaceae member Gallibacterium anatis is a major cause of salpingitis and peritonitis in poultry, resulting in decreased egg production and increased mortality worldwide. The bacterium show high antigenic diversity and a high level of antibiotic resistance, which makes prevention and control of disease by traditional vaccines and treatments insufficient.
Outer membrane vesicles (OMVs) are produced by virtually all Gram negative bacteria and show an enormous functional diversity in both host-interactions and virulence factor delivery. OMVs contain outer membrane proteins and periplasmic contents and several studies have shown their potential as vaccine candidates. We have shown that G. anatis produce OMVs and that their protein contents are influenced by their surroundings. This indicates a highly regulated function and release of the OMVs, which might aid in survival and virulence of the bacteria (Bager et al. 2013. Infect. Immun. 81, 1964-73), while on the other hand OMVs may serve as a multipotent vaccine prototype. To explore this possibility further, a ∆tolR mutant of G. anatis was engineered and shown to release large quantities of OMVs compared to the wild type and preliminary in vivo studies indicated a protective potential of these ∆tolR OMVs. The TolR protein belongs to the Tol-Pal pathway, which is important for membrane integrity. The mutant could therefore represent a cost-effective alternative to traditional vaccines. Current experiments aim at further elucidating this potential by looking at the presence of a selected panel of putative universal antigens within the OMVs. Furthermore, we are working on antigen enrichment of the OMVs by targeting universal antigens to the periplasma through a signal sequence from the outer membrane protein OmpA. Hopefully this will result in OMVs capable of offering increased and serotype-independent protection against Gallibacterium anatis.