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Characterisation, recombinant expression and immunogenicity of BHLP29.7, an outer membrane lipoprotein of Brachyspira hyodysenteriae

La, Tom (2006) Characterisation, recombinant expression and immunogenicity of BHLP29.7, an outer membrane lipoprotein of Brachyspira hyodysenteriae. PhD thesis, Murdoch University.

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Swine dysentery (SD) is an important endemic infection in many piggeries, and control can be problematic. In this study, the gene encoding a 29.7 kDa outer membrane lipoprotein of the causative intestinal spirochaete Brachyspira hyodysenteriae, was identified and sequenced. An 816 bp hypothetical open reading frame (ORF) was identified, with a potential ribosome binding site, and putative -10 and -35 promoter regions upstream from the start of the ORF. The 29.7 kDa outer membrane lipoprotein was designated Bhlp29.7 and the encoding gene named bhlp29.7.

The amino acid sequence of Bhlp29.7 included a 19 residue hydrophobic signal peptide, incorporating a potential signal peptidase cleavage site and membrane lipoprotein lipid attachment site. In silico analysis of this protein together with lipidation studies further supported its probable outer membrane localisation. Comparison of the Bhlp29.7 sequence with public sequence databases showed that it had up to 40% similarity with the D-methionine substrate-binding outer membrane lipoprotein (MetQ) of a number of bacterial pathogens. The Bhlp29.7 gene was detected in all 48 strains of B. hyodysenteriae examined, and in Brachyspira innocens strain B256T, but not in 10 other strains of B. innocens or in 42 strains of other Brachyspira spp. The gene was sequenced from B. innocens strain B256T and from 11 strains of B. hyodysenteriae. The B. hyodysenteriae genes shared 97.9-100% nucleotide sequence identity and had 97.5-99.5% identity with the gene of B. innocens strain B256T. The Bhlp29.7 gene was subsequently cloned and expressed as a histidine fusion protein in an Escherichia coli expression system.

An ELISA test using recombinant his-tagged Bhlp29.7 (His6-Bhlp29.7) as the detecting antigen was developed and evaluated. The threshold value of the test was chosen to provide a highly stringent assessment of the disease status of a herd. The sensitivity and specificity of the test was 100%. When the test was applied to sera from eight herds with suspected SD, four gave ELISA values indicating that the herds were diseased. The remaining four herds gave ELISA values below the threshold value. These results indicated that the Bhlp29.7-ELISA was useful as an indirect test for exposure of a herd to B. hyodysenteriae and may be a helpful complement to current methods of SD diagnosis.

Recombinant His6-Bhlp29.7 was evaluated as a vaccine subunit for prevention of SD. The His6-Bhlp29.7 was shown to be immunogenic in mice following two intramuscular injections. Vaccination of mice with His6-Bhlp29.7 provided full protection after oral challenge with B. hyodysenteriae. In two experiments, intramuscular and oral vaccination of pigs with the His6-Bhlp29.7 resulted in a 50% reduction in incidence of SD compared to unvaccinated control pigs (P=0.047). This is the first subunit vaccine shown to provide pigs with protection from SD. Further work is needed to optimise delivery routes and adjuvants for commercial development of the vaccine.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Biomedical Sciences
Supervisor(s): Hampson, David
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