| Research Abstract |
Shigellae cause bacillary dysentery in humanas, and this constitutes a major public health problem in developing countries. The early essential step leading to dysenteric symptoms is invasion of colonic epithelial cells, followed by intraellular bacterial multiplication and spread of invading bactera to adjacent cells.
In Shigella flexneri, various chrmosomal loci have been shown to be associated with its pathogenicity. While on the large (230 kb) plasmid of S. flexneri, seven choromosomal loci (virF, virB, ipaBCD, Region-3, -4, and -5, and virG) have been identified by our previous studies. One of the plasmid born virulence locus, virG, was shown to be required for the invading bacteria to spread intracellularly and intercellularly through inducing the aggregation of F-actin. The expression of the virG gene was indicated to be under the controls of the transcriptional activation by the virF gene and the post-transcriptional regulaion by one of the chromosomal locus, kcpA. To identify genes on the choromosome associated with the virulence phenotypes of the primary invation, multiplication and spread, approximately 10.000 Tn5 insertion mutants were isolated by using an in vitro assay system. Fifty mutants with reduced virulence were characterized with respect to their virulence phenotypes, including three different mutations that affect invasion of epithelial cells, bacterial metabolism and structures of lipopolysaccharide. Assignment of the fifty Tn5 insertions of the mutansts to the 19 NotI restriction fragments of the chromosomal DNA has permitted the identification of at least nine virulence-associated chromosome loci. These study will become basis for the molecular study on the role of each virulence locus in the spread of invading bacteria to the adjacent epithelial cells.
|
