Listeria monocytogenes, an opportunistic enteric pathogen, remains a significant cause of foodborne illness worldwide. L. monocytogenes is the causative agent of listeriosis, a potentially fatal condition characterized by bacteremia and meningitis or meningoencephalitis. Individuals at risk for listeriosis include individuals with suppressed cell-mediated immune systems, such as pregnant women, neonates, AIDS patients, and the elderly. L. monocytogenes has been and remains a significant public health threat because of its hardy nature and ability to grow at refrigeration temperatures. Understanding how to better prevent illness could significantly lower the mortality rate due to this foodborne pathogen. The objective of this research is to determine if increase in Firmicute populations during stages of estrus will provide colonization resistance against L. monocytogenes. The results of this study could allow the development of preventive treatments for high risk individuals, pregnant women and women attempting to become pregnant. The findings of this project would allow us to see if the estrus cycle plays a role in resistance to L. monocytogenes. The research also looks at growth curves of the L. monocytogenes to see how the life cycle and concentrations of the pathogen affect the results.