| Summary: | 碩士 === 臺北醫學大學 === 醫學科學研究所 === 96 === Salmonella is an important food-borne pathogen of public health concern. Sal-monella enterica contains more than 2,500 serotypes among which Typhimurium is an important etiology of gastroenteritis. Adhesion of bacteria to the host epithelial cells is a prerequisite step in establishing infection, while fimbriae are the primary structures implicated in such an adherent event. The type 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium. The strongly fimbriate-phase bacteria can be isolated following serial passage every 48 hours in static broth culture, while non-fimbriate bacteria are obtained by growth on solid agar media. The phenotypic expression of type 1 fimbriae in S. Typhimurium is the result of the interaction and cooperation of several genes in the fim gene cluster. A transposon insertion mutagenesis has revealed that several genes outside the fim gene cluster may also involve in the expression of type 1 fimbriae both in static broth and on solid agar culture conditions. One S. Ty-phimurium mutant ubiB constitutively produced type 1 fimbriae in both culture condi-tions. The ubiB gene could encode a NAD(P)H-flavin reductase. Southern hybri-dization indicated that the transposition event occurred once in this mutant strain. Transforming the plasmid pTA-ubiB that contained the coding sequence of ubiB con-ferred the ubiB mutant back to the type 1 fimbrial phenotype as seen in the parental strain as indicated by yeast agglutination and electron microscopy. Reverse tran-scription polymerase chain reaction (RT-PCR) indicated that the fimA expression of the ubiB mutant strain obtained from the static broth was about 1.2% of that obtained from the solid agar culture. When ubiB strain harbored the plasmid pTA- ubiB, the fimA expression from broth was about 34 fold of that from the solid agar. As a con-trol, 16S rRNA was constantly expressed in all the strains tested. Growth curve analysis suggested that ubiB mutant had a slower growth rate in the log phase than the parental strain and the ubiB (pTA- ubiB) strain. How ubiB gene product affects type 1 fimbrial expression in S. Typhimurium is of interest and warrants further investiga-tion.
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