Abstract
ABSTRACTWith a broad range of hosts, Salmonella enterica serovar Typhimurium (S. Typhimurium) is the major cause of gastroenteritis in human beings and systemic disease in susceptible mice strains. However, different S. Typhimurium strains differ in regard to virulence and host adaptation. Here, C57BL/6 mice were infected, respectively, with different S. Typhimurium strains SL1344 (calf), CVCC541 (chicken) and CMCC50115 (mutton) to determine their virulence and host immune responses. It was found that mice were less susceptible to infection by S. Typhimurium CVCC541 and CMCC50115 strains, with lower lethality and decreased bacterial burden in liver and spleen. Besides, S. Typhimurium strains CVCC541 and CMCC50115 enhanced host innate immune responses by increased frequencies of macrophages and neutrophils 3 days after infection. But SL1344 strain evaded immune response by inducing apoptosis of macrophages. Moreover, CVCC541 could elicit adaptive immune responses of host 11 days after infection upon examination of the proliferation and activation of CD4+ T cells. In addition, 125 and 138 unique mutant coding genes, respectively, in S. Typhimurium strains CVCC541 and CMCC50115 and 78 shared mutant coding genes were annotated by genomic alignment to SL1344 genome and the signal pathways involving these genes were further analyzed. The acquired results indicate that different original S. Typhimurium strains show differential virulence and may induce diverse immune responses in the same host infected.
Highlights
Salmonella enterica, composed of distinct serovars based on surface antigens, are capable of infecting a wide range of hosts [1], while S. enterica serovar Typhimurium
The results showed that SL1344-infected mice carried significantly higher bacterial burdens than CVCC541- and CMCC50115-infected mice at 3 days after infection
The upregulated levels of proinflammatory cytokines IL-1β, IL-6 and TNFα in the serum of mice infected by SL1344 manifested their stronger resistance to bacterial infection, which implied that the SL1344 had posed higher virulence to hosts
Summary
Salmonella enterica, composed of distinct serovars based on surface antigens, are capable of infecting a wide range of hosts [1], while S. enterica serovar Typhimurium Typhimurium) exists as the most prototypical serovar associated with human and animal disease. Typhimurium is rare by bloodstream infection in human. Typhimurium strains such as ST313, showing genetic differences compared to other S. Typhimurium strains, might cause bloodstream infection characterized by fever [2,3,4]. S. Typhimurium can induce differential responses in the same hosts, which can be related to virulence factors of different strains and various host immune responses. It is vital to study the interplay between hosts and different S. Typhimurium strains to better understand the etiology of new pathogens
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