Macrophage apoptosis associated with <i style="">Salmonella enterica </i>serovar Typhi plasmid

Abstract

The present study was undertaken to investigate the relationship between plasmid isolated from <i style="">S. enterica</i><i style=""> </i>serovar

Typhi (pR_ST98) and macrophage apoptosis. pR_ST98 was transferred into an attenuated <i style="">S.</i><i style=""> enterica </i>serovar Typhimurium strain RIA to create a transconjugant pR_ST98/RIA. Standard <i style="">S.</i><i style=""> enterica </i>serovar Typhimurium virulence strain SR-11 was used as a positive control, and RIA as a negative one. Murine macrophage-like cell line (J774A.1) was used as an infectious cell model <i style="">in</i><i style=""> vitro. </i>In order to determine the inhibition and bactericidal effect of amikacin (AMK) to extracellular bacteria and the best optimization co-culture ratio between <i style="">Salmonella </i>and J774A.1, the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of AMK to strains SR-11, pR_ST98/RIA and RIA and multiplicity of infection (MOI) were detected first, and then J774A.1 was infected by the above three serovar Typhimurium strains. Apoptosis of J774A.1 was examined with electron microscopy and flow cytometry after annexin-V/propidium iodide labeling at 0, 1, 3, 6, 12 and 24 h. Mitochondrial membrane potential was detected by JC-1 staining method. It was demonstrated that MIC of AMK to the three strains was 10µg/ml, MBC was 80µg/ml, and optimal MOI was 100:1. pR_ST98/RIA resulted in a higher apoptosis of J774A.1 than RIA, apoptotic features such as chromatin margination could be observed after 3 h, and death of J774A.1 cells was associated with the loss of mitochondrial membrane potential. These results indicated that pR_ST98 could enhance the virulence of its host bacteria, evidenced by increased macrophage apoptosis.