Examining Committee
Dr. Massimo Marcone, Chair
Dr. Gisele LaPointe, Advisor
Dr. Jeffrey Farber, Co-Advisor
Dr. Keith Warriner, Department Member

TITLE: STUDIES ON THE SURVIVAL OF LISTERIA MONOCYTOGENES IN FLUID MILK PRODUCTS AFTER EXPOSURE TO GASTRIC FLUIDS USING THE SHIME® AS A SIMULATOR OF THE STOMACH OF HUMAN ADULTS

ABSTRACT: Listeria monocytogenes is an opportunistic foodborne pathogen which has been implicated in many outbreaks of foodborne diseases. The thesis examined the survival of L. monocytogenes under acid and chlorine stresses which it encounters inside the host or in the food processing environment, respectively. The Simulator of the Human Intestinal Microbial System (SHIME) was used to simulate the gastric conditions of human adults. The survival rates of L. monocytogenes inoculated in milk products after a 2-hour exposure to simulated gastric fluid with pH values of 1.5, 2.0 and 3.0 were 0.003 to 0.040%, 22.7 to 43.4% and 16.6 to 27.2%, respectively. The survival of L. monocytogenes depended on a combination of factors, including gastric acidity, gastric digestion time, L. monocytogenes strain, food type and recovery method. The exposure of L. monocytogenes to 3.5 ppm chlorine induced L. monocytogenes into the viable but non-culturable state (VBNC).  The cells in the VBNC state showed signs of resuscitation and growth after 24 hours of incubation in milk products at 4˚C.