Impact of Plasmids, Including Those EncodingVirB4/D4 Type IV Secretion Systems, on Salmonella enterica serovar Heidelberg Virulence in Macrophages and Epithelial Cells

Abstract

Salmonella enterica serovar Heidelberg (S. Heidelberg) can cause foodborne illness in humans following the consumption of contaminated meat and poultry products. Recent studies from our laboratory have demonstrated that certain S. Heidelberg isolated from food-animal sources harbor multiple transmissible plasmids with genes that encode antimicrobial resistance, virulence and a VirB4/D4 type-IV secretion system. This study examines the potential role of these transmissible plasmids in bacterial uptake and survival in intestinal epithelial cells and macrophages, and the molecular basis of host immune system modulation that may be associated with disease progression. A series of transconjugant and transformant strains were developed with different combinations of the plasmids to determine the roles of the individual and combinations of plasmids on virulence. Overall the Salmonella strains containing the VirB/D4 T4SS plasmids entered and survived in epithelial cells and macrophages to a greater degree than those without the plasmid, even though they carried other plasmid types. During entry in macrophages, the VirB/D4 T4SS encoding genes are up-regulated in a time-dependent fashion. When the potential mechanisms for increased virulence were examined using an antibacterial Response PCR Array, the strain containing the T4SS down regulated several host innate immune response genes which likely contributed to the increased uptake and survival within macrophages and epithelial cells.

Identification of a novel plasmid-mediated colistin-resistance gene, mcr-2, in Escherichia coli, Belgium, June 2016

“…enterica serovar Heidelberg plasmid pSH146_32 (GenBank accession number JX258655), with 98% identity and 90% query coverage. Several Salmonella-associated virulence genes were found on pKP37-BE, including virB/D4 that encodes a type 4 secretion system [11].…”

“…IncX4 plasmids have also been previously shown to harbour mcr-1 [21] as well as extended spectrum beta-lactamase genes, bla CTX-M [20]. Interestingly, the pKP37-BE backbone, which likely originated from Salmonella spp., harboured a battery of virulence genes including the virB4/D4 genes encoding a type-IV secretion system that has been shown to mediate downregulation of host innate immune response genes and an increased bacterial uptake and survival within macrophages and epithelial cells [11]. Outer membrane modifications leading to colistin resistance have been shown to attenuate virulence [22]: whether these co-harboured virulence genes are able to compensate the pathogenic abilities of colistin-resistant E. coli remains to be explored.…”

An Inducible and Secreted Eukaryote-Like Serine/Threonine Kinase of Salmonella enterica Serovar Typhi Promotes Intracellular Survival and Pathogenesis

“…Other secretory systems reported for eSTKs include Legionella pneumophila Dot/Icm, a T4SS for the secretion of LegK1 to LegK4, and SecA2 for M. tuberculosis PknG (14). The Salmonella enterica serovar Heidelberg plasmid-encoded T4SS enhances the ability to invade and survive within intestinal epithelial and macrophage cell lines, perhaps through the suppression of innate host immune responses (31). In addition, the T6SS gene cluster of S. Typhimurium is required for optimal virulence in mice, perhaps due to its role in macrophage survival and replication (32).…”

Cytotoxic Mechanism ofCytolethal Distending Toxinin NontyphoidalSalmonellaSerovar (SalmonellaJaviana) During Macrophage Infection

“…Javiana were cultured overnight in LB broth at 37°C. On the day of infection, bacteria were subcultured, harvested upon reaching an OD 600 = 0.600-0.800, and were resuspended in culture media for infection (multiplicity of infection = 1:200) with a slight modification in the method described earlier (Raffatellu et al, 2005;Gokulan et al, 2013;Han et al, 2013). In brief, bacteria were added to the macrophage monolayer (three sets of macrophages in duplicate for adherence, invasion, and persistence).…”