Oral Presentation International Pasteurellaceae Conference 2014

The chameleon effect: Pasteurella multocida lipopolysaccharide polymorphism and its contribution to host mimicry and vaccine escape (#36)

Marina Harper 1 , Frank St Michael 2 , Marietta John 3 , Conny Turni 4 , Pat Blackall 4 , Ben Adler 1 , Andrew D. Cox 2 , John D. Boyce 3
  1. Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, Monash University, Melbourne, VIC, Australia
  2. Institute for Biological Sciences, National Research Council, Ottawa, ON, Canada
  3. Monash University, Clayton, VIC, Australia
  4. Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD, Australia
Pasteurella multocida is the causative agent of a wide range of animal diseases, including bovine haemorrhagic septicaemia, atrophic rhinitis in pigs and fowl cholera. It is widely believed that bacterin vaccines afford excellent protection against strains belonging to the same lipopolysaccharide (LPS) serovar (as determined by Heddleston serotyping). However, the efficacy of serovar-specific protection has never been objectively tested as neither the accuracy of Heddleston serotyping nor the range of LPS glycoforms/structures produced by different P. multocida strains has been known. Using our knowledge of LPS structure and genetics, we have replaced the Heddleston serotyping system with an LPS multiplex PCR that accurately groups P. multocida strains into 8 LPS genotypes. The most common strains isolated from poultry belong to LPS genotype L3 (including Heddleston serovar 3 and 4 strains) and L6 (including Heddleston serovar 10, 11, 12 and 15 strains). LPS structural analyses of over 25 field isolates belonging to genotypes L3 and L6 revealed that many related, but structurally distinct, LPS glycoforms are produced by different isolates from within a single genotype. Moreover, in some L3 field isolates, multiple LPS glycoforms are simultaneously produced by the one strain; many of these glycoforms mimic vertebrate glycosphingolipids. The existence of genetically related field isolates producing a wide range of LPS glycoforms, with some strains producing many glycoforms simultaneously, raises significant questions about the ability of existing P. multocida bacterins to elicit protection against even closely related strains. Indeed, analysis of a persistent fowl cholera outbreak on an Australian poultry farm found that strains isolated before and after vaccination were related but the post-vaccination isolates expressed altered LPS, raising the possibility that mutants expressing altered LPS structures can escape vaccine-induced host immunity.