| Salmonella is an important zoonotic pathogen with more than 2600 Salmonella serotypes,and birds is one of the most crucial hosts of Salmonella.Avian Salmonella can cause poultry chronic or acute infectious diseases,clinical symptoms included enteritis,sepsis,etc.Salmonella Pullorum(S.Pullorum)has strict host specificity for poultry.Transmission of S.Pullorum occurs not only vertically but also horizontally,and the infection causes Pullorum disease in chicks,characterized by white diarrhea resulting in death,which bringing immeasurable economic losses to the poultry industry.Bacteria must activate relevant adaptive mechanisms to adapt to changes of the external environment.Stringent response(SR)is an important adaptation mechanism mediated by the signal molecule(p)ppGpp,which is synthesized by(p)ppGpp synthetases.In this study,molecular epidemiological analysis of avian Salmonella in central China was carried out to analyze the role of(p)ppGpp mediated SR of S.Pullorum in environmental adaptation and pathogenicity.Serotype analysis of 84 isolates of Salmonella isolated from central China showed that Salmonella serogroup D was the main subgroup,accounting for 84.76%,of which S.Pullorum was the primary serotype,accounting for 45.24%.Antimicrobial resistance analysis revealed that all isolates exhibited higher resistance rates to colistin,tetracycline and ampicillin.Multilocus sequence typing(MLST)analysis displayed that there were 9 genotypes in avian Salmonella isolates,of which ST92 was the primary serotype.There was a strong connection between genotypes and serotypes in Salmonella.To investigate the role of(p)ppGpp synthetases in the adaptation and pathogenicity of S.Pullorum,this study constructed(p)ppGpp synthetases mutant Δrel AΔspo T.Bacteria biological characteristics tests shows that comparded with wild-type strain,the growth rate of mutant Δrel AΔspo T was significantly faster under amino acid starvation,and the MBCs of mutant Δrel AΔspo T of erythromycin,ampicillin,tetracycline and ciprofloxacin significantly decreased,the survival rate of mutant Δrel AΔspo T significantly decreased under the condition of acid,alkali and high osmotic pressure.Cell infection tests showed that comparded with wild-type strain,the adhesion and invasion rates of mutant Δrel AΔspo T significantly decreased within DF-1 cells,about 5times and 40 times respectively,and the internalization ability of wild-type strain was0.114%±0.117%,and mutant strain was 0.037%±0.015%,which was significantly reduced.Animal tests have shown that compared with wild-type strain,the contents of mutant Δrel AΔspo T were significantly lower in liver and caecum of infected chickens.For infecton group survived,30% and 100% died in wild-type strain and mutantΔrel AΔspo T infection groups,respectively.Transcription profiling showed the expressing of 865 genes were significantly changed under amino acid starvation.Compared with wild-type strain,539 genes were down-regulated and 326 genes were up-regulated in mutant strain.The expression of genes-related ribosomal subunits,DNA replication and transcription,associated with the growth of S.Pullorum,were significantly up-regulated in mutant strain.Compared with wild-type strain,T3 SS device proteins(inv AEFG,spa PQ,prg H)and other effector proteins(sip ABCD,Sop BDE)encoded by SPI-1 were significantly down-regulated in mutant strain,which are associated with adhesion and invasion.Other down-regulated genes include superoxide dismutase(sod1,sod2)and T3 SS effector proteins(sse ABCDFGJ,sif A,pip B2)encoded by SPI-2,which are mainly related to the survival and proliferation of macrophages.Our study showed(p)ppGpp synthetases play a crucial role in environmental adaptation and pathogenicity of S.Pullorum.This study established foundation for a comprehensive understanding of(p)ppGpp synthetases and regulation mechanism of pathogenicity of S.Pullorum. |
PDF Full Text Request