RESUMO
Salmonella enterica serovar Choleraesuis strain C500 is a live attenuated vaccine that has been widely used in Chi‐na for over 50 years to prevent piglet paratyphoid .However ,as C500 is obtained by chemical methods ,the genetic background of this strain remained unclear .In this study ,we compared the genomic differences between the virulent reference strain C 78‐2 and C500 by suppression subtractive hybridization combined with the mirror orientation selection method (MOS‐SSH ) .Six genes (asr ,ydgF ,ydgD ,ydgE ,rpoS ,and ptsG) were lost in C500 strain .Using real‐time PCR analysis ,we demonstrated that the genes regulated by rpoS ,a vital transcriptional regulator playing an important role in Salmonella infection ,were downregulated in C500 .Additionally ,the virulence of the rpoS mutant strain C78‐2ΔrpoS was 100 000 times lower than the parental strain in BALB/c mice .So loss of rpoS gene is the major factor leading to the attenuation of C500 strain .
RESUMO
Proteins encoded by regions of difference (RD) of Mycobacterium tuberculosis (MTB) constitute a potential source of specific antigens for vaccine development and immunodiagnosis .In the present study ,four genes named nrdF1 , pe_pgrs35 ,rv1985c ,and rv1986 from RD2 of MTB were cloned and overexpressed in E .coli with the induction of IPTG .Western blotting assay showed that these recombinant fusion proteins could well react with anti-His tag monoclonal antibody ,which in-dicated their good immunoreactivity .The serodiagnosis potential applications of these four proteins in bovine tuberculosis were further evaluated .An indirect ELISA assay was established by using fusion proteins as coating antigens for detection of their specific antibodies in bovine sera .The positive rates were 7 .35% in NrdF1 ,22 .06% in PE_PGRS35 ,16 .18% in Rv1985c and 16 .18% in Rv1986 respectively .All the results suggest that these fusion proteins have the potential application in serodiagnosis of bovine tuberculosis .