ABSTRACT
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 .
ABSTRACT
Pullorum disease affecting poultry is caused by Salmonella enterica serovar Pullorum and results in severe economic loss every year, especially in countries with a developing poultry industry. The pathogenesis of S. Pullorum is not yet well defined, as the specific virulence factors still need to be identified. Thus, to isolate specific DNA fragments belonging to S. Pullorum, this study used suppression subtractive hybridization. As such, the genome of the S. Pullorum C79-13 strain was subtracted from the genome of Salmonella enterica serovar Gallinarum 9 and Salmonella enterica serovar Enteritidis CMCC(B) 50041, respectively, resulting in the identification of 20 subtracted fragments. A sequence homology analysis then revealed three types of fragment: phage sequences, plasmid sequences, and sequences with an unknown function. As a result, several important virulence-related genes encoding the IpaJ protein, colicinY, tailspike protein, excisionase, and Rhs protein were identified that may play a role in the pathogenesis of S. Pullorum.
