Disease Resistance Studies in Pigs

<p>Salmonella-induced macrophage lysis and its significance in pathogenesis/host specificity is unclear. The role of specific virulence genes and the macrophage response to infection is being assessed in Salmonella/macrophage interactions using different Salmonella serotypes and sources of macrophages. Lysis is mediated by factors encoded on both the Salmonella chromosome and virulence plasmid. Two novel loci that influence macrophage lysis have been identified. One locus shows homology to the faeI gene of E. coli that encodes a fimbrial protein. The other locus shows no homology to any sequences on databases. Macrophage lysis is independent of the state of macrophage activation, and not mediated by TNFa. The role of the virulence plasmid in vivo and the significance of macrophage lysis in pathogenesis remain unclear.</p>

<p>We have shown that the plasmid influences the recruitment of inflammatory cells to foci of infection in mice, however the Tn mutants that show reduced macrophage lysis in vitro are fully virulent in mice. Salmonella-induce macrophage lysis is both serotype and host dependent. Strains of S. typhimurium, S. dublin but not S. choleraesuis lyse bovine macrophages, while none of these serotypes efficiently lyse porcine macrophages. Salmonella- induced macrophage lysis is not associated with features characteristic of apoptosis. Salmonella persistence within macrophages and associated differential expression of pro- inflammatory cytokines does not correlate with host specificity. Studies characterising Salmonella/macrophages interactions in vivo are ongoing.</p>