Abstract
Plasmid pRST98 is a hybrid antibiotic resistance-virulence plasmid isolated fromSalmonella enterica serovar Typhi (S. Typhi). Previously, we transferred pRST98 into attenuated Salmonella enterica serovar Typhimurium (S. typhimurium) strain RIA to create a transconjugant pRST98/RIA and indicated that pRST98 could enhance apoptosis of infected murine macrophages J774A.1. However, S. typhimurium-mice interaction cannot reflect all characteristics of S. typhi-human interaction. The present study 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 to gain more precise and further insight into the role of pRST98 in interaction between S. typhi and human macrophage. Macrophage apoptosis, caspase-3 activity and nitric oxide (NO) production were assayed. The results demonstrated that macrophages infected with ST8 and ST8-c-pRST98 displayed more extensive apoptosis than those infected with ST8-ΔpRST98. Further studies showed that pRST98 could increase caspase-3 activity and suppress NO production. Pretreated macrophages with NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) enhanced S. Typhi-induced macrophage apoptosis. The research data indicate that the plasmid pRST98 can enhance caspase-3 mediated macrophage apoptosis by suppressing NO production. Key words: Salmonella enterica serovar Typhi, plasmid pRST98, macrophage, apoptosis, nitric oxide, caspase-3 activity.
Highlights
Typhoid fever, known as enteric fever, is caused by Salmonella typhi, a gram-negative bacterium classified as a serovar of the species Salmonella enterica
The relationship between pRST98 and macrophage apoptosis was further confirmed by flow cytometer analysis after propidium iodide (PI) staining
There was no significant difference between macrophage apoptosis induced by ST8, ST8-ΔpRST98 and ST8-cpRST98 (P > 0.05)
Summary
Known as enteric fever, is caused by Salmonella typhi, a gram-negative bacterium classified as a serovar of the species Salmonella enterica. The symptoms of patients with typhoid fever usually present with a history of prolonged fever, headache, abdominal discomfort and general lethargy. Typhoid fever has decreased in recent years. It remains a serious public health problem in developing and even in developed countries (Crump and Mintz, 2010). According to the estimation of the World Health Organization (WHO), 22 million typhoid fever cases occur each year, 5% of which are fatal. The treatment of infected patients has become complicated as S. typhi acquires a considerable variety of genes by plasmids moving between bacteria through conjugation, such as, antibiotic-resistance and virulence genes (Morita et al, 2010)
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