Abstract
Poultry are the main source of human infection by Salmonella. As infected poultry are asymptomatic, identifying infected poultry farms is difficult, thus controlling animal infections is of primary importance. As cell tropism is known to govern disease, our aim was therefore to identify infected host-cell types in the organs of chicks known to be involved in Salmonella infection and investigate the role of the three known invasion factors in this process (T3SS-1, Rck and PagN). Chicks were inoculated with wild-type or isogenic fluorescent Salmonella Typhimurium mutants via the intracoelomic route. Our results show that liver, spleen, gall bladder and aortic vessels could be foci of infection, and that phagocytic and non-phagocytic cells, including immune, epithelial and endothelial cells, are invaded in vivo in each organ. Moreover, a mutant defective for the T3SS-1, Rck and PagN remained able to colonize organs like the wild-type strain and invaded non-phagocytic cells in each organ studied. As the infection of the gall bladder had not previously been described in chicks, invasion of gall bladder cells was confirmed by immunohistochemistry and infection was shown to last several weeks after inoculation. Altogether, for the first time these findings provide insights into cell tropism of Salmonella in relevant organs involved in Salmonella infection in chicks and also demonstrate that the known invasion factors are not required for entry into these cell types.
Highlights
Salmonella spp. are among the most important foodborne pathogens
Mutant strains defective for the T3SS-1 or the three known invasion factors inoculated by the intracoelomic route colonize chicks more effectively than their wild-type parent strain
Previous work has shown that a ΔinvA::kan mutant (ΔinvA) mutant strain (T3SS-1 defective strain) and a strain deleted for the three known invasion factors (3Δ) remained invasive for several eukaryotic cell lines compared to the wild-type strain [31]
Summary
Salmonella spp. are among the most important foodborne pathogens. From a public health perspective, according to the World Health Organization, Salmonella spp. are among the 31 diarrhoeal and/or invasive agents (viruses, bacteria, protozoa, helminths and chemicals) displaying the highest capability of triggering intestinal or systemic diseases in humans. The two most commonly reported non-typhoïdal serovars Salmonella enterica subsp. Enterica serovar Enteritidis and Salmonella enterica subsp. Enterica serovar Typhimurium (including its monophasic variant) account for almost 80% of human cases occurring in the EU [2]. Depending on host factors and serovars, Salmonella can induce a wide range of diseases ranging from systemic to asymptomatic infections and gastroenteritis [3]. In humans, localized infections can be followed by bacteraemia in 3–10% of cases [4]
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