Interaction of Salmonella serotypes with porcine macrophages in vitro does not correlate with virulence

Abstract

The interaction between Salmonella serotypes and macrophages is potentially instrumental in determining the outcome of infection. The nature of this interaction was characterized with respect to virulence and serotype-host specificity using pigs as the infection model. Experimental infection with Salmonella typhimurium , Salmonella choleraesuis or Salmonella dublin resulted in enteric, systemic or asymptomatic infection, respectively, which correlates well with the association of S. choleraesuis with systemic disease in pigs in epidemiological studies. Persistence within porcine alveolar macrophages in vitro did not directly correlate with virulence since S. typhimurium persisted in the highest numbers, and S. choleraesuis in the lowest. Comparison to other studies revealed that the relatively high persistence of S. typhimurium in macrophages correlates with its virulence in a broad range of animals : this could be a virulence mechanism for broad-hostrange serotypes. There were little or no significant differences in the induction of pro-inflammatory cytokines by macrophages infected with the three serotypes. S. typhimurium and S. dublin, but not S. choleraesuis, damaged porcine macrophages, and the mechanism of damage did not resemble apoptosis. In conclusion, the virulence of Salmonella serotypes in pigs did not directly correlate with their interaction with porcine macrophages in vitro. The interaction of Salmonella and macrophages in vitro may not accurately model their interaction in vivo, and this will form the basis of further study.

Net Replication ofSalmonella entericaSerovars Typhimurium and Choleraesuis in Porcine Intestinal Mucosa and Nodes Is Associated with Their Differential Virulence

“…Serovar Typhimurium 4/74 and serovar Choleraesuis A50 have been described previously, and their virulence in pigs is well defined (53). The behavior of these strains in cultured cells and animals is comparable to that of other strains of the same serovar (3,34,53), and the clinical symptoms they elicit are typical of field isolates.…”

“…Serovar Typhimurium 4/74 and serovar Choleraesuis A50 have been described previously, and their virulence in pigs is well defined (53). The behavior of these strains in cultured cells and animals is comparable to that of other strains of the same serovar (3,34,53), and the clinical symptoms they elicit are typical of field isolates. Plasmid pHSG422 (23) was kindly provided by T. Hashimoto-Gotoh, Kyoto, Japan, and was electroporated into the Salmonella strains with selection for resistance to ampicillin (100 g/ml) and kanamycin (50 g/ml) at 25°C.…”

“…Indeed, strains of serovars that are systemically avirulent in these hosts following oral inoculation, including serovar Typhimurium, exhibited increased invasion (9,34,47) and elicited greater enteropathogenic responses (34,47). Furthermore, although the natural resistance-associated macrophage protein is important in the control of systemic serovar Choleraesuis infection in pigs (48), strains of serovar Choleraesuis do not exhibit an ability to survive better in porcine primary alveolar macrophages compared to serovar Typhimurium and no significant differences in the induction of proinflammatory cytokines in cultured porcine alveolar macrophages by the serovars could be detected (53). It has been noted that host-restricted serovars persist better in mesenteric lymph nodes, indicating that bacterial net growth at intestinal sites may be an important determinant of systemic virulence (34,47).…”

Molecular insights into farm animal and zoonoticSalmonellainfections

“…The systemic virulence of S. enterica serovar Dublin (S. Dublin) in cattle cannot be attributed to survival in primary macrophages, macrophage lysis (Watson et al 2000a), damage to intestinal epithelia (Bolton et al 1999), enteritis (Paulin et al 2002) or to the magnitude of invasion of the ileal mucosa (Bolton et al 1999;Paulin et al 2002). Broadly, the same applies to the systemically virulent serovars Abortusovis in sheep (Uzzau et al 2001), Choleraesuis in pigs (Watson et al 2000b) and Gallinarum in chickens (Chadfield et al 2003), compared with the broad host-range serovar Typhimurium.…”

Antigen selection based on expression levels during infection facilitates vaccine development for an intracellular pathogen

“…Quantitative gene expression analysis of intracellular pathogens in infected tissues is generally hampered by the large excess of host RNA and protein. As an approximation, pathogen transcriptomes (6) and proteomes (7) have been analyzed in cell culture infection models, but such in vitro models imperfectly reproduce conditions in infected animals (8)(9)(10)(11). Various reporter genes such as chloramphenicol acetyltransferase and GFP can be used to qualitatively detect gene expression in infected animals, and this permitted identification of several in vivo expressed genes of Salmonella and other pathogens (12,13).…”