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Abstract
The Gram-negative anaerobic bacterium Dichelobacter nodosus (Dn) causes footrot in ruminants, a debilitating and highly contagious disease that results in necrotic hooves and significant economic losses in agriculture. Vaccination with crude whole-cell vaccine mixed with multiple recombinant fimbrial proteins can provide protection during species-specific outbreaks, but subunit vaccines containing broadly cross-protective antigens are desirable. We have investigated two D. nodosus candidate vaccine antigens. Macrophage Infectivity Potentiator Dn-MIP (DNO_0012, DNO_RS00050) and Adhesin Complex Protein Dn-ACP (DNO_0725, DNO_RS06795) are highly conserved amongst ~170 D. nodosus isolates in the https://pubmlst.org/dnodosus/ database. We describe the presence of two homologous ACP domains in Dn-ACP with potent C-type lysozyme inhibitor function, and homology of Dn-MIP to other putative cell-surface and membrane-anchored MIP virulence factors. Immunization of mice with recombinant proteins with a variety of adjuvants induced antibodies that recognised both proteins in D. nodosus. Notably, immunization with fimbrial-whole-cell Footvax vaccine induced anti-Dn-ACP and anti-Dn-MIP antibodies. Although all adjuvants induced high titre antibody responses, only antisera to rDn-ACP-QuilA and rDn-ACP-Al(OH)3 significantly prevented rDn-ACP protein from inhibiting lysozyme activity in vitro. Therefore, a vaccine incorporating rDn-ACP in particular could contribute to protection by enabling normal innate immune lysozyme function to aid bacterial clearance.
Highlights
Dichelobacter nodosus is a rod shaped, gram negative, obligate anaerobe, non-spore forming bacterium that causes footrot in ruminants[1,2]
We present a study on i) the antigenicity of monovalent recombinant (r)Dichelobacter nodosus (Dn)-MIP and rDn-ACP proteins, using a wide variety of adjuvants, in comparison with commercial Footvax vaccine; ii) describe putative structural features of both proteins based on sequence comparison and structure prediction; iii) characterize Dn-ACP, which has two homologous domains to Neisseria spp. lysozyme inhibitor molecules[29,30], as the first lysozyme inhibitor protein to be reported in D. nodosus
For dn-mip 25 alleles were identified that grouped into 9 non-redundant alleles for 166 isolates; no allele could be defined for 6 isolates (Supplementary Table 2, Supplementary Fig. 2A)
Summary
Dichelobacter nodosus (formerly Bacteroides nodosus and Fusiformis nodosus) is a rod shaped, gram negative, obligate anaerobe, non-spore forming bacterium that causes footrot in ruminants[1,2]. Vaccination against D. nodosus reduces disease prevalence[6] and monovalent whole-cell[7,8] and mono-, bi- or multi-valent recombinant fimbrial vaccines[9,10,11] can provide protection during footrot outbreaks[12,13]. We present a study on i) the antigenicity of monovalent recombinant (r)Dn-MIP and rDn-ACP proteins, using a wide variety of adjuvants, in comparison with commercial Footvax vaccine; ii) describe putative structural features of both proteins based on sequence comparison and structure prediction; iii) characterize Dn-ACP, which has two homologous domains to Neisseria spp. lysozyme inhibitor molecules[29,30], as the first lysozyme inhibitor protein to be reported in D. nodosus
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