| Salmonella enterica serovar Typhimurium(S.Typhimurium)is an important human food-borne pathogen.The range of the host for this pathogenic bacteria is wide.S.Typhimurium can infect mice and cause systemic diseases similar to human typhoid fever;it can also infect humans and cause self limiting gastroenteritis.The vast majority of Salmonella typhimurium only causes gastroenteritis when it infects humans.However,the recently emerged virulent strain of Salmonella typhimurium D23580 in sub-Saharan Africa can infect people with low immunity and cause systemic bacteremia.However,the evolutionary mechanisms of the virulent strain of Salmonella typhimurium D23580 and the molecular mechanisms that cause systemic diseases in humans are not yet fully understood.In this study,we selected the model strain of Salmonella Typhimurium 14028(14028s)and the virulent strain of Salmonella typhimurium D23580(D23580)as the research objects,and used a variety of animal models to comprehensively detect the pathogenicity of these two strains.The results of lethal experiments in mice,gavage experiments and intraperitoneal injection experiments show that D23580 has a lethal effect on mice.The colonization ability in the mouse intestine,and its replication ability in mouse liver and spleen are significantly higher than that of 14028 s.Consistent with mouse experiments,the results of in vitro macrophage replication experiments(mouse macrophages RAW 264.7 and human macrophages U937)also showed that the replication ability of D23580 in the two types of macrophages was also significantly higher than that of 14028 s.In order to further study the molecular mechanisms of the difference in toxicity and pathogenicity between 14028 s and D23580,we conducted an analysis of these two strains in RPMI 1640 medium,respectively,infecting murine macrophages and human macrophages through comparative transcriptomics.The differences in gene expression of cells under the three conditions were compared.According to the change trends of gene expression in 14028 s and D23580,we further divided these genes into genes with the same expression change trend(both up-regulated or down-regulated)and inconsistent expression change trends(up-regulated in one strain,down-regulated in another strain).The inconsistent gene expression trends in 14028 s and D23580 may be related to the difference in pathogenicity of the two strains.We found that the genes with the different changing trend were mainly concentrated in three pathways: ko00650 butyrate metabolism pathway,ko00920 sulfur metabolism pathway and ko00770 pantothenic acid and Co A biosynthesis pathway.Furtherly,we selected pantothenic acid and Co A biosynthesis pathways for in-depth research.We blocked the biosynthesis pathway of pantothenic acid and Co A by deleting ilv C,ilv D and STMMW＿35201(the gene number is STM14＿4251 in S.Typhimurium 14028)in14028s and D23580,and tested the effect of these genes on the pathogenicity of14028 s and D23580.The results of mouse experiments and cell experiments showed that the lack of ilv C,or ilv D,STM14＿4251(STMMW＿35201)induced significantly reduction in the replication ability and pathogenicity in D23580.These results indicated that D23580 can significantly increase its replication in macrophages by activating the biosynthetic pathway of pantothenic acid and Co A,which may be part of the reason why D23580 can evolve into a virulent strain.The results of this study are of great significance for the comprehensive understanding of the evolutionary mechanisms of the virulent strain of Salmonella typhimurium D23580 and the molecular mechanisms that cause human systemic diseases.At the same time,the key genes in the biosynthetic pathway of pantothenic acid and Co A that we discovered can be used as candidate targets for related vaccines and antibacterial drugs,providing new methods and ideas for the prevention and treatment of Salmonella typhimurium infection. |
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