IV Jornadas Latinoamericanas de Bacteriófagos

Bacteriophages are increasingly explored as vaccine platforms due to their stability, intrinsic immunogenicity, and capacity to display antigens. In mycobacterial diseases such as paratuberculosis (caused by Mycobacterium avium subsp. paratuberculosis, MAP), the identification of protective antigens remains challenging. The use of antibody-selected phages allows the identification of immunogenic epitopes. The aim of this project was to evaluate a phage-based vaccine composed of bacteriophages and to compare its protective performance with that of a conventional inactivated MAP vaccine, in a murine challenge model. Three bacteriophages were selected from a commercial phage display library (#E8100S, New England Biolabs) by biopanning, using pooled sera from MAP-immunized cattle, and formulated as a vaccine containing a total of 1X1012 PFU. BALB/c mice (n=38) received two immunizations three weeks apart. Control groups included mice inoculated with PBS, a non-selected phage, or heat-inactivated MAP. Three weeks after the second immunization, mice were challenged intraperitoneally with either 10⁸ or 10⁹ CFU of a bovine MAP isolate and followed during 6–7 weeks (CICUAL #2024/26). Protection was assessed by histopathological scoring and quantification of viable MAP recovered from liver tissue. Mice that received the antibody-selected phage vaccine showed reduced hepatic bacterial burden and predominantly mild granulomatous lesions compared with animals vaccinated with inactivated MAP, which frequently developed moderate to severe lesions associated with high bacterial recovery. Mice receiving a non-selected phage showed heterogeneous outcomes: although hepatic MAP recovery was consistently lower than in mice vaccinated with selected phages, histopathological scores were slightly higher when animals were challenged with the lower MAP dose (10⁸ CFU). Taken together, our results would support the potential use of bacteriophages enriched by host-derived antibody recognition, for the development of targeted vaccines against paratuberculosis.