Efficacy of bacteriophage Lysed Pasteurella marker vaccine in laboratory animal models with a novel DIVA for haemorrhagic septicaemia

OBJECTIVE: The present study aimed at evaluating the efficacy of an improved phage lysate marker vaccine for haemorrhagic septicaemia in mice and rabbit model and development of a DIVA ELISA based on iron restricted outer membrane protein (IROMP). METHOD: The experimental vaccine was prepared by lysing P. multocida B:2 grown under iron restricted conditions with a Pasteurella bacteriophage and addition of an alum adjuvant to enhance the immunogenicity. The vaccine was administered in mice and rabbits divided into two group each. Phage lysate vaccine (PL-VacI) was administered to group I mice and rabbits whereas group II mice and rabbits received alum precipitated HS vaccine (HS-VacII). Antibody titres were monitored 0, 30, 60, 90, 210 and 240 dpv. An IROMP (130 kDa) based indirect ELISA was also developed to differentiate between infected and vaccinated animals. The Pasteurella phage isolated in present study was sequenced at Georgia Genomic Facilty, Georgia. RESULT: The sequence of PMP-GAD-IND (Pasteurella bacteriophage) was deposited in GenBank under no KY203335. The group I mice and rabbits vaccinated with Phage lysate vaccine (PL-VacI) group revealed significantly higher antibody titres than group II mice and rabbits receiving alum-precipitated bacterin (HS-VacII) by MAT, IHA and ELISA (P < 0.05 and P < 0.001). The peak log (10) values (3.46) in case of group I mice by ELISA were attained at 90DPI whereas in group II mice the peak values at 90DPI were 2.82. Mean log(10) titres by ELISA in group I and II rabbits were 2.43 and 2.35 respectively at 30DPI whereas at 120DPI the titres were 3.29 and 2.75, respectively. The DIVA ELISA detected presence of a novel 137 kDa IROMP/siderophore antibody in sera of group I mice and rabbits (PL-VacI) absent in sera of mice and rabbits given HS-VacII. CONCLUSION: The bacteriophage based marker vaccine (PL-VacI) had a more effective and longer immune response against HS in mice and rabbit in comparison to the widely used alum precipitated HS vaccine (HS-VacII). Moreover, the development of a recombinant IROMP based indirect ELISA could serve as an excellent tool to differentiate between infected and vaccinated cattle and buffaloes for effective control of HS.