Date of Award


Degree Type

Honors College Thesis

Academic Program

Biological Sciences BS


Biological Sciences

First Advisor

Janet Donaldson, Ph.D.

Advisor Department

Biological Sciences


Listeria monocytogenes is a deadly foodborne bacterium that is responsible for almost 20% of food-related deaths in the United States. Listeria monocytogenes contaminates ready-to-eat products such as cheese, deli meat, and ice cream. Once ingested, it invades the intestinal lining and can enter the bloodstream, causing listeriosis. There is a gap in the knowledge of the pathogenesis of L. monocytogenes in how it is able to survive in the gastrointestinal tract in the presence of bile, which has bactericidal properties. Previous studies have suggested that the second messenger cyclic-dimeric-GMP may be involved in the regulation of virulence factors of Listeria. This nucleotide is produced by diguanylate cyclases and degraded by phosphodiesterases. The purpose of this study was to determine whether phosphodiesterase D was responsible for bile survival and if oxygen availability influences the impact of this phosphodiesterase. Survival of the wild-type strain (F2365) and the pdeD mutant was analyzed in aerobic and anaerobic conditions in neutral and acidic pH with and without 1% bile to mimic locations within the body where bile would be present (i.e. duodenum and gall bladder). Results showed that the pdeD mutant was more sensitive to bile in anaerobic and acidic conditions than the wild type. In order to better understand the relationship between PdeD and bile, real-time qPCR was conducted to determine if there were differences in the expression of bsh in pdeD and F2365. Bsh is the bile salt hydrolase that is used to detoxify bile. Using the 16S gene as an internal control, it was found that there was a slight decrease in expression of bsh in pdeD than F2365, though this change was not significant. These data suggest that the phosphodiesterase D may be involved in responding to bile-induced damage, but does so independently of the bsh expression. The v reduction in bile survival exhibited by this strain suggests that the phosphodiesterase may be responsive to oxidative stress. Further research is needed to determine if the regulation of the pdeD is due to exposure to oxidative stress.

Included in

Bacteriology Commons