The Effects of host physiological conditions on the expression of icsP in Shigella flexneri

Shigella flexneri is a gram-negative bacterium capable of causing diarrhea and dysentery known as shigellosis. It is estimated there are 167.4 million shigellosis episodes throughout the world each year causing 1.1 million deaths. Shigella invades cells in the lower intestine through an induced phagocytosis. Once in the cytoplasm, bacteria move from one cell to another using actin-based motility. The Shigella outer membrane protease IcsP regulates actin-based motility and cell-to-cell spread by cleaving the actin assembly protein IcsA from the bacterial cell surface. We hypothesize that IcsP may serve additional functions during infection. By examining which environmental signals trigger icsP expression, we aim to identify other regions of the body where IcsP might function. Shigellae are exposed to an array of environmental conditions in the body. We examined the presence of bile salts, low pH, and anaerobic conditions in this study. Expression of icsP and IcsP levels were assessed in bacteria grown under each of these physiological conditions using β-galactosidase assays and western blots, respectively. Growth of Shigella strains was reduced in the presence of deoxycholate, a common bile salt, as compared to the control. In stationary growth phase, icsP expression increased when the bacteria were grown in the presence of bile salts. Growth of Shigella in medium buffered at pH 5.5 was slightly elevated (\u3c10% more growth) when compared to bacteria grown in medium at pH 7.4. We also found that anaerobic conditions negatively impact the growth of Shigella. Expression of icsP has not yet been measured under this condition