An in vivo expression technology (IVET) was applied to screen s.flexneri 2a genes induced after invasion of epithelial cells, and virulence-related genes were further identified by mutational analysis. Thirteen intracellular induced genes were identified with a HeLa cell infection model. Of these, two were identified as alkylation-related genes; one was related to metabolism; one encoded a transcriptional regulator; three were identified as insertion elements; three ap- peared to be antisense to genes involved in the transmethylation,biosyntheseis, and phos- photransferase system;and three were predicted to encode polypeptides with unknown functions. Intracellular survival assavs showed that the mutants of alkA,citC and wcaJ genes had lower capability of intracellular replication or survival than the the wild-type strain.The results indicated that alkA, citC and wcaJ genes could take part in the intracellular survival or replication of S. flexneri 2a and the capability of intracellular survival or replication could be one of the major virulence elements. However, the yaiC mutant was able to survive in the murine infection assay but almost not in HeLa cell infection assay. Very possibly, yaiC gene was involved in the other mechanism of S. flexneri virulence. This study might lead to a better understanding of the intra- cellular survival or proliferation process of S. flexneri 2a and perhaps provide insights into the pathogenicity of this pathogen.
SHI ZhaoxingWANG HengliangHU KunFENG ErlingYAO XiaoHUANG LiuyuSU GuofuHUNAG PeitangHUANG Cuifen
Comparative Genomic Hybridization (CGH) microarray analysis was used tocompare the genomic compositions of all eighteen Shigella boydii serotype representative strains.The results indicated the genomic ''backbone'' of this subgroup contained 2552 ORFs homologous tononpatho-genic E. coli K12. Compared with the genome of K12199 ORFs were found to be absent in allS. boydii serotype representatives, including mainly outer membrane protein genes and O-antigenbiosynthesis genes. Yet the specific ORFs of S. boydii subgroup contained basically bacteriophagegenes and the function unknown (FUN) genes. Some iron metabolism, transport and type Ⅱ secretionsystem related genes were found in most representative strains. According to the CGH phylogeneticanalysis, the eighteen S. boydii serotype representatives were divided into four groups, in whichserotype C13 strain was remarkably distinguished from the other serotype strains. This groupingresult corresponded to the distribution of some metabolism related genes. Furthermore, the analysisof genome backbone genes, specific genes, and the phylogenetic trees allowed us to discover theevolution laws of S. boydii and to find out important clues to pathogenesis research, vaccinationand the therapeutic medicine development.
