Shigella flexneri is a Gram negative facultative anaerobe that infects millions world-wide each year. The route for infection of a host is through the intestinal and rectal epithelium layers, but it also can survive in the environment. Different genes have been found to be up regulated depending upon its presence in the intracellular or extracellular environment, as shown in previous work in the lab. This thesis seeks to examine the role these upregulated genes, bioA and lysA, play in the intracellular activity of S. flexneri. Knock-out mutations in the bioA and lysA genes were created using P1 transduction. To test the effects of these mutations on S. flexneri, plaque, invasion, and attachment assays were performed. It was found that the bioA mutation resulted in fewer plaques being formed, while the lysA mutation resulted in slower forming and incompletely lysed plaques being formed. / text