The Homolog of the Gene <i>bstA</i> of the BTP1 Phage from Salmonella enterica Serovar Typhimurium ST313 Is an Antivirulence Gene in Salmonella enterica Serovar Dublin

Abstract

In a previous study, a novel virulence gene, <i>bstA</i>, identified in a <i>Salmonella enterica</i> serovar Typhimurium sequence type 313 (ST313) strain was found to be conserved in all published <i>Salmonella enterica</i> serovar Dublin genomes. In order to analyze the role of this gene in the host-pathogen interaction in <i>S</i> Dublin, a mutant where this gene was deleted (<i>S</i> Dublin Δ<i>bstA</i>) and a mutant which was further genetically complemented with <i>bstA</i> (<i>S</i> Dublin 3246-C) were constructed and tested in models of <i>in vitro</i> and <i>in vivo</i> infection as well as during growth competition assays in M9 medium, Luria-Bertani broth, and cattle blood. In contrast to the results obtained for a strain of <i>S</i> Typhimurium ST313, the lack of <i>bstA</i> was found to be associated with increased virulence in <i>S</i> Dublin. Thus, <i>S</i> Dublin Δ<i>bstA</i> showed higher levels of uptake than the wild-type strain during infection of mouse and cattle macrophages and higher net replication within human THP-1 cells. Furthermore, during mouse infections, <i>S</i> Dublin Δ<i>bstA</i> was more virulent than the wild type following a single intraperitoneal infection and showed an increased competitive index during competitive infection assays. Deletion of <i>bstA</i> did not affect either the amount of cytokines released by THP-1 macrophages or the cytotoxicity toward these cells. The histology of the livers and spleens of mice infected with the wild-type strain and the <i>S</i> Dublin Δ<i>bstA</i> mutant revealed similar levels of inflammation between the two groups. The gene was not important for adherence to or invasion of human epithelial cells and did not influence bacterial growth in rich medium, minimal medium, or cattle blood. In conclusion, a lack of <i>bstA</i> affects the pathogenicity of <i>S</i> Dublin by decreasing its virulence. Therefore, it might be regarded as an antivirulence gene in this serovar.