Poster Presentation The Prato Conference on the Pathogenesis of Bacterial Infections of Animals 2016

Understanding how Pasteurella multocida lipopolysaccharide diversity impacts the efficacy of live and killed fowl cholera vaccines (#60)

Marina Harper 1 , Marietta John 1 , Mark Edmunds 1 , Amy Wright 1 , Mark Ford 2 , Conny Turni 3 , Pat Blackall 3 , Ian Wilkie , Andrew D Cox 4 , Ben Adler 1 , John D Boyce 1
  1. Microbiology , Infection and Immunity Program, Monash Biomedicine Discovery Institute, Monash University, Melbourne, Victoria
  2. CSIRO Livestock industries, Australian Animal Health Laboratory, Geelong, Victoria, Australia
  3. Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia
  4. Vaccine Program, Human Health Therapeutics Portfolio, National Research Council, Ottawa, Ontario, Canada

Pasteurella multocida is a Gram-negative bacterium and the causative agent of many serious animal diseases, including fowl cholera in poultry. Strains have traditionally been differentiated into 16 serological LPS types based on the Heddleston gel diffusion precipitin test developed in the 1970s. Both killed-cell and live attenuated fowl cholera vaccines are available, but a true understanding of how to achieve solid, cross-protective immunity has remained elusive. Strains selected for inclusion into an autologous, killed vaccine are often chosen based on the LPS Heddleston serovar of recent local outbreak strains. However, we have shown that Heddleston serotyping does not accurately predict the LPS structure produced by strains and have developed a multiplex PCR that accurately differentiates P. multocida into eight LPS genotypes based on the outer core LPS loci1. To assess the true cross-protective efficacy of both killed and live P. multocida vaccines we conducted vaccination trials using a range of genetically and structurally defined P. multocida strains belonging to LPS genotypes 1 and 3, each expressing either full length or a truncated LPS structure. Killed-cell vaccines elicted protection only against challenge strains expressing identical or nearly identical LPS. In contrast, a cross-protective immune response was generated by vaccination with the live attenuated P. multocida strains. These data raise significant questions about the ability of existing P. multocida killed-cell vaccines to protect against new outbreak strains or vaccine-induced escape mutants. Furthermore they show that protection mediated by live vaccines is cross-protective and indicate that this immune response is directed against conserved non-LPS components expressed by P. multocida.

1 Harper M et al. Development of a rapid multiplex PCR assay to genotype Pasteurella multocida strains by use of the lipopolysaccharide outer core biosynthesis locus. J. Clin. Microbiol. 2015 53:477-485.