Only one of the two type VI secretion systems encoded in the Salmonella enterica serotype Dublin genome is involved in colonization of the avian and murine hosts

Abstract

The type VI secretion system (T6SS) is a virulence factor for many Gram-negative bacteria. Salmonella genus harbors five phylogenetically distinct T6SS loci encoded in Salmonella Pathogenicity Islands (SPIs) SPI-6, SPI-19, SPI-20, SPI-21 and SPI-22, which are differentially distributed among serotypes. The T6SSs encoded in SPI-6 and SPI-19 contribute to pathogenesis of serotypes Typhimurium and Gallinarum in mice and chickens, respectively. Salmonella Dublin is a pathogen restricted to cattle where it causes a systemic disease. Also, it can colonize other hosts such as chickens and mice, which can act as reservoirs of this serotype. Salmonella Dublin harbors the genes for both T6SSSPI-6 and T6SSSPI-19. This study has determined the contribution of T6SSSPI-6 and T6SSSPI-19 to host-colonization by Salmonella Dublin using avian and murine models of infection. Competitive index experiments showed that, a mutant strain lacking both T6SSs (∆T6SSSPI-6/∆T6SSSPI-19) presents a strong colonization defect in cecum of chickens, similar to the defect observed for the ∆T6SSSPI-6 mutant, suggesting that this serotype requires a functional T6SSSPI-6 for efficient colonization of the avian gastrointestinal tract. Colonization of mice was also defective, although to a lesser extent than in chickens. In contrast, the T6SSSPI-19 was not necessary for colonization of either chickens or mice. Transfer of T6SSSPI-6, but not T6SSSPI-19, restored the ability of the double mutant to colonize both animal hosts. Our data indicate that Salmonella Dublin requires only the T6SSSPI-6 for efficient colonization of mice and chickens, and that the T6SSSPI-6 and T6SSSPI-19 are not functionally redundant.

The SPI-19 encoded type-six secretion-systems (T6SS) of Salmonella enterica serovars Gallinarum and Dublin play different roles during infection

“…Typhimurium (Sana et al, 2016), however, only in vivo data with CFU counts from the intestine of infected animals would allow a firm conclusion in this matter . The result is in contrast to previous reporting, where only the T6SS of S. Dublin encoded in SPI6 was shown to affect virulence, while the SPI19/T6SS was dispensable (Pezoa et al, 2014). The T6SS consists of 13 highly conserved T6SS core proteins each of which belongs to a specific COG (Boyer et al, 2009).…”

Relevant Genes Linked to Virulence Are Required for Salmonella Typhimurium to Survive Intracellularly in the Social Amoeba Dictyostelium discoideum

“…Salmonella mutants harboring deletions of clpV or T6SS loci present defects in intracellular survival in macrophages (Haneda et al, 2009; Mulder et al, 2012; Blondel et al, 2013) and systemic colonization in mice and chicken (Mulder et al, 2012; Pezoa et al, 2013, 2014). It has been reported that bacterial pathogens like Vibrio cholerae and Burkholderia cenocepacia require specific T6SS to survive predation by D. discoideum (Pukatzki et al, 2006; Aubert et al, 2008; Zheng et al, 2011).…”

H-NS Silencing of the Salmonella Pathogenicity Island 6-Encoded Type VI Secretion System Limits Salmonella enterica Serovar Typhimurium Interbacterial Killing

“…Indeed, the SPI-6 T6SS was first identified as a modulator of intracellular proliferation in macrophages (46,49). Recent studies further revealed that the SPI-6 T6SS is an important actor for virulence toward mice and for chicken gastrointestinal colonization (50)(51)(52). The undetectable level of T6SS expression under in vitro conditions suggests that these genes are silenced and that this silencing might be counteracted in vivo.…”