Salmonella enterica serovar Typhi plasmid pR ST98 enhances intracellular bacterial growth and S. typhi-induced macrophage cell death by suppressing autophagy

objectives: plasmid prst98 is a hybrid resistance-virulence plasmid isolated from salmonella enterica serovar typhi (s. typhi). previous studies demonstrated that prst98 could enhance the virulence of its host bacteria. however, the mechanism of prst98-increased bacterial virulence is still not fully elucidated. this study was designed to gain further insight into the roles of prst98 in host responses. methods: human-derived macrophage-like cell line thp-1 was infected with wild-type (st8), prst98-deletion (st8-δprst98), and complemented (st8-c-prst98) s. typhi strains. macrophage autophagy was performed by extracting the membrane-unbound lc3-i protein from cells, followed by flow cytometric detection of the membrane-associated fraction of lc3-ii. intracellular bacterial growth was determined by colony-forming units (cfu) assay. macrophage cell death was measured by flow cytometry after propidium iodide (pi) staining. autophagy activator rapamycin (rapa) was added to the medium 2 h before infection to investigate the effect of autophagy on intracellular bacterial growth and macrophage cell death after s. typhi infection. results: plasmid prst98 suppressed autophagy in infected macrophages and enhanced intracellular bacterial growth and s. typhi-induced macrophage cell death. pretreatment with rapa effectively restricted intracellular bacterial growth of st8 and st8-c-prst98, and alleviated st8 and st8-c-prst98-induced macrophage cell death, but had no significant effect on st8-δprst98. conclusions: plasmid prst98 enhances intracellular bacterial growth and s. typhi-induced macrophage cell death by suppressing autophagy.