Genetic Stability Of Salmonella Typhi And Salmonella Paratyphi A In Experiment Microevolution

Objective Typhoid fever was caused by Salmonella Typhi or Paratyphi A, B, and C. It is a public health problem worldwide. Recently, paratyphoid fever became more severe than typhoid fever in China and some Southeast Asian countries, and the performance of the endemic area gradually expanded. Although S. Typhi and S. Paratyphi A has the same host specificity, similar mechanism of transmission and clinically similar enteric fever, Paratyphi A became predominant pathogen of typhoid fever in some regions. We focused on that if the different genetic stability leading to the emergence of paratyphoid epidemic. According to the perspective of disease surveillance, we monitored the S. Typhi and S. Paratyphi A after laboratory evolution by molecular typing. We observed the genetic stability of S. Typhi and S. Paratyphi in experiment microevolution and explored the possible mechanisms of genomic mutations.Methods CT18, ATCC9150, two S. Typhi strains and two S. Paratyphi A strains provided by Institute of Communicable Disease Prevention and Control Center for Disease Control and Prevention, China, were selected because CT18 and ATCC9150 have been sequenced, and the other 4 strains are predominant strains which caused typhoid fever in China in the mid-1990s. The 6 strains were divided into S. Typhi and S. Paratyphi A subgroups. The isolated colony of the 6 strains was incubated at 37℃in a rotating water bath. After 12 h,100μl of a 10-4 dilution was aliquoted into 9.9 ml of LB. This 12h incubation-aliquoting into LB cycle was done for 20 times. The isolated colonies of the end point (20 times) were analyzed by pulsed field gel electrophoresis (PFGE), rRNA rearrangement and prophage detecting.Results The 96x6 isolated strains of the end point (20 times) have been analyzed by PFGE. The colonies of three S. Typhi strains showed different changes, the rates of CT18, GX-039 and GZ-902115 were 66.7%,63.5% and 5.21%, respectively, while no change was observed for the colonies of three S. Paratyphi A. Furthermore, we determined the rrn arrangement of CT18-43 which was a isolated colony of CT18 and its rrn was rearranged during laboratory evolution. In addition, we also found some genes in prophage3 were deleted during laboratory evolution. The positive isolated colony is from GZ-902115 (GZ-902115-85).Conclusion During laboratory evolution, the PFGE patterns of isolated colonies from three S. Typhi changed. The change of PFGE pattern indicated there were some mutations on the genome. Each S. Typhi strain's percentage of changed isolates varied greatly because their genome had many different variations. But the colonies of three S. Paratyphi A strains were very conserved and their PFGE patterns is unchanged. Some variations such as rRNA rearrangement and gene deletion among prophage area were detected on the colonies'genome which can be responsible for the changes of PFGE patterns partly. Objective To analyze molecular typing and characteristic of pathogen evolution of Salmonella paratyphi A strains.Methods Pulsed-field gel electrophoresis (PFGE) with SpeⅠas the restriction enzyme was used to analyze Salmonella paratyphi A strains from 10 provinces during 2000-2008. The genomic DNA in different Salmonella paratyphi A strains were also identified by multilocus sequence typing (MLST), under PCR products of housekeeping genes aroC,thrA,hisD,purE,sucA,dnaN,hemD,adk and purA.Results One hundred and eighteen Salmonella paratyphi A strains isolated in China in different years were quite different in PFGE fingerprints, and there were 32 kinds of PFGE fingerprints in total. However, data from MLST revealed lack of diversity among the strains of the same serotype and the number of variable nucleotide sites ranged from 1 to 20 between Salmonella paratyphi A and other serotypes of Salmonella. Conclusion Currently in China, high degree clonal strains caused paratyphoid fever epidemic spreading throughout the country. With the year changing, a number of sporadic mutations occurred.