An official website of the United States government.
The overall goal of this research is to understand what factors influence the ability of Listeria monocytogenes to cause systemic disease following ingestion of contaminated food products. The hypothesis to be tested in the proposed project is, that growth of L. monocytogenes on ready to eat meat products triggers a phenotypic response that allows the listerial cells to better survive within the g.i. tract, translocate across the intestinal mucosa, or migrate to and multiply within the target organs of listeriosis (i.e. spleen, liver, CNS, placenta). There are 2 specific aims: 1) Compare the virulence for mice of L. monocytogenes grown on turkey slices with that of listerial cells grown in bacteriologic broth (brain heart infusion); and 2) Compare the ability of L. monocytogenes grown on turkey slices or in BHI broth for their ability to adhere to, invade, and multiply within human intestinal epithelial cells (differentiated Caco-2 cells).
NON-TECHNICAL SUMMARY: Listeria monocytogenes is an important and costly foodborne pathogen, that has caused serious outbreaks after ingestion of contaminated ready to eat turkey meat. In this study we will determine whether growth on turkey meat triggers changes in L. monocytogenes that make it better able to invade intestinal cells and cause systemic infection. <P>
APPROACH: Listerial cells will be harvested from mid-log phase cultures growing in packages of sliced turkey meat and their virulence compared with the same strains grown in BHI broth, using i.g. inoculated A/J mice as our model system. Mice will be anesthetized and inoculated i.g. with the desired dose of L. monocytogenes (in 0.2. ml) using a blunt-end feeding needle. The severity of infection will be assessed by recovery of L. monocytogenes from the intestinal tract, spleen, liver and other tissues, and by histopathological examination of the same tissues. We then will assess how growth in packages of turkey slices affects the ability of L. monocytogenes to attach to, invade and survive within the Caco-2 human intestinal epithelial cell line.
<P>
PROGRESS: 2005/02 TO 2009/01<BR>
OUTPUTS: Experiments have been performed to compare the growth of L. monocytogenes on several types of turkey product, and assess the effect on the severity of infection in a mouse model of gastrointestinal listeriosis. Substantial growth of L. monocytogenes strain 2365 was seen on several types of sliced ready to eat turkey meat in a 7 to 10 day incubation period at 10 degrees C. Listerial cells grown on turkey meat, emulsified in turkey meat, or grown in BHI broth did not differ in their ability to cause systemic infection in intragastrically (i.g.) inoculated A/J mice. In contrast, growth of L. monocytogenes in packages of turkey meat increased the listerial cells survival when suspended in synthetic gastric fluid at pH 7.0, 5.0 or 3.5. The difference was most notable with late logarithmic growth phase listerial cells; stationary phase cells showed less effect after growth on sliced turkey meat. The increased resistance of listerial cells was not duplicated by growth of L. monocytogenes in BHI at a lower pH. Glucose in the BHI broth (0.2%) might be responsible in part for the decreased resistance to synthetic gastric fluid. . We also examined the effects of growth on turkey meat on invasion of intestinal epithelial cells, and on other phenotypic properties of listerial cells in vitro. A long term goal was to ascertain what components in turkey meat increase the resistance of listerial cells, and what regulatory pathways in the listerial cells are elicited by growth on turkey meat that accounts for the enhanced resistance in synthetic gastric fluid. <BR>PARTICIPANTS: The work described in this report involved principally the efforts of Nancy Faith (Sr. Research Specialist) and Luke Peterson M.S. The latter received his M.S. in 2006 for his work on this project. We have collaborated with Dr. Sophia Kathariou (NC State), Brien Neudeck (Univ. Tenn. Med. Ctr.) and John Luchansky (USDA ARS Wyndmoor, PA) on our listeriosis research. Campus colleagues who have offered helpful advice related to this project include Drs. Amy Wong, Chuck Kaspar and Kathy Glass. <BR>TARGET AUDIENCES: The target audience for this research includes other academic investigators with an interest in listeriosis, and food industry microbiologists with an interest in the pathogenesis of listeriosis after ingestion of a contaminated food product. <BR><BR>
IMPACT: 2005/02 TO 2009/01<BR>
The overall goal of this project was to determine whether the growth of Listeria monocytogenes on ready to eat meat might alter the listerial cells in a way that would make them better able to survive the harsh environment in the g.i. tract and cause systemic infection. Results from our study were presented to the biomedical research community and to representatives of the food industry in a variety of venues. These included presentations at the XVIth International Symposium on Problems of Listeriosis (ISOPOL) in March 2007, at a National Alliance for Food Safety and Security Symposium at the Executive Committee Meeting of the National Restaurant Association held in Rogers, AR in October 2007, and at the International Association for Food Protection meeting in August 2008.