The spv genes on the Salmonella dublin virulence plasmid are required for severe enteritis and systemic infection in the natural host

Abstract

The pathogenic role of the spv (Salmonella plasmid virulence) genes of Salmonella dublin was determined in the natural, bovine host. Since the lack of overt signs of enteritis or enterocolitis due to Salmonella infections in mice has limited the development of a convenient experimental system to study enteric disease, we used calves to study the contribution of the spv genes to S. dublin-induced salmonellosis. Since the SpvR transcriptional regulator is required for expression of the spvABCD operon, we constructed an spvR knockout mutation in a calf-virulent strain of S. dublin. Calves were infected with the wild-type strain, an spvR mutant, and an spvR mutant containing a complementing plasmid. Calves that were infected with the wild type or the complemented spvR mutant rapidly developed severe diarrhea and became moribund. Calves that were infected with the spvR mutant showed little or no clinical signs of systemic salmonellosis and developed only mild diarrhea. The survival and growth of the wild-type strain and the spvR mutant were determined by using blood-derived bovine monocytes. Wild-type S. dublin survived and grew inside cells, while the spvR mutant did not proliferate. These results suggest that the spv genes of S. dublin promote enhanced intracellular proliferation in intestinal tissues and at extraintestinal sites in the natural host.

Exploratory cohort study to determine if dry cow vaccination with aSalmonellaNewport bacterin can protect dairy calves against oralSalmonellachallenge

“…The next morning, a volume with the expected concentration of Salmonella Typhimurium was mixed with 1 L of milk replacer and 2.5 g of sodium bicarbonate, 2.5 g of magnesium trisilicate, and 2.5 g magnesium hydroxide to alkalinize the abomasum. 10 Slight differences in inoculum dose occurred based on variability in the overnight growth of the isolate. The inoculum in milk was fed to the calf at the morning feeding on day 0.…”

The Salmonella virulence plasmid spv genes are required for cytopathology in human monocyte-derived macrophages

“…To demonstrate that the macrophage phenotype de®ned for the spv locus in S. typhimurium is not speci®c to that serovar, we tested wild-type S. dublin SL2260 and the corresponding spvR mutant SL2403 (Libby et al, 1997) in the human macrophage assay. The results of a time course experiment, shown in Fig.…”

“…The ®ve Salmonella spvRABCD genes were originally discovered on large plasmids present in certain serovars belonging to the S. enterica subspecies I lineage Guiney et al, 1994;. The plasmid-encoded spv locus was shown to be required for progressive systemic infection by strains pathogenic for mice and for the virulence of host-adapted serovars in their corresponding animal hosts (Chikami et al, 1985;Gulig and Curtiss, 1987;Barrow et al, 1987;Heffernan et al, 1987;Danbara et al, 1992;Wallis et al, 1995;Libby et al, 1997). Recently, the spv genes have been found to have a wide distribution among ancestral lineages of S. enterica, being present on the chromosome in subspecies II, IIIa and VII, as well as in some isolates of subspecies IV (Boyd and Hartl, 1998).…”

“…However, attempts to de®ne a phenotype in vitro for the spv genes during infection of mouse macrophages or murine cell lines have been unsuccessful (Gulig and Curtiss, 1987;Rijkonen et al, 1992). Recently, an spvR mutant of S. dublin was found to have a slower growth rate than the wild-type parent strain in bovine monocyte-derived macrophages (Libby et al, 1997). These encouraging results led us to develop an assay for the spv phenotype in human monocyte-derived macrophages.…”

The Salmonella spvB virulence gene encodes an enzyme that ADP‐ribosylates actin and destabilizes the cytoskeleton of eukaryotic cells

“…Evidence obtained in vivo suggests that the spv genes act to enhance bacterial replication in macrophages (Fields et al, 1986;Gulig and Doyle, 1993). Recently, studies of Salmonella infection in bovine monocyte-derived macrophages have indicated that the spv genes are required for bacterial growth (Libby et al, 1997). Furthermore, expression of the spv genes is required for Salmonella strains to induce cytotoxicity in infected human monocyte-derived macrophages, characterized by cell detachment and eventual apoptosis (Libby et al, 2000).…”