Abstract
In order to better identify the role of the Salmonella pathogenicity island 2 (SPI-2) type III secretion system (T3SS) in chickens, we used the well-known gentamicin protection assay with activated HD11 cells. HD11 cells are a macrophage-like chicken cell line that can be stimulated with phorbol 12-myristate 13-acetate (PMA) to exhibit more macrophage-like morphology and greater production of reactive oxygen species (ROS). Activated HD11 cells were infected with a wild-type Salmonella enterica subspecies enterica serovar Typhimurium (S. Typhimurium) strain, a SPI-2 mutant S. Typhimurium strain, a wild-type Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) strain, a SPI-2 mutant S. Enteritidis strain, or a non-pathogenic Escherichia coli (E. coli) strain. SPI-2 mutant strains were found to survive as well as their parent strain at all time points post-uptake (PU) by the HD11 cells, up to 24 h PU, while the E. coli strain was no longer recoverable by 3 h PU. We can conclude from these observations that the SPI-2 T3SS of S. Typhimurium and S. Enteritidis is not important for survival of Salmonella in the activated macrophage-like HD11 cell line, and that Salmonella must employ other mechanisms for survival in this environment, as E. coli is effectively eliminated.
Highlights
Infections by Salmonella enterica subspecies enterica are one of the leading causes of food borne gastroenteritis in humans [1]
At 3, 6, 12, and 24 h PU, viable E. coli DH5a were no longer recoverable from the cell monolayer fraction (Figure 3, panels B–E). This observation indicates that even though more viable E. coli DH5a bacteria were recovered 0.5 h PU compared to the Salmonella strains, it is clear that the HD11 cells are able to effectively kill the E. coli strain after the initial infection process
At 0.5 h PU, prior to addition of gentamicin, more E. coli DH5a were recovered from the cell monolayer fraction than the Salmonella strains
Summary
Infections by Salmonella enterica subspecies enterica are one of the leading causes of food borne gastroenteritis in humans [1]. Among those serovars responsible for food poisoning in humans, serovars Typhimurium Enteritidis) are most commonly isolated serovars from both humans and animals in many regions. Typhimurium is the primary serovar isolated from both humans and animals, while S. Enteritidis is the second most common serovar isolated from humans. Enteritidis being the number one isolate from both humans and animals and S. Enteritidis are capable of causing systemic disease in humans, this is not the normal course of infection and only occurs in very young, very old, and immunocompromised individuals [3]
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