MSc Defence - VIVIAN LY "Survival and Virulence of Listeria Monocytogenes During Long-Term Storage on Chocolate Liquor, Corn Flakes and Dry-Roasted Pistachios"

Examining Committee
Dr. Paul Spagnuolo, Chair
Dr. Jeff Farber, Advisor
Dr. Gisele LaPointe, Advisory Committee Member
Dr. Lawrence Goodridge, Department Member

TITLE: SURVIVAL AND VIRULENCE OF LISTERIA MONOCYTOGENES DURING LONG-TERM STORAGE ON CHOCOLATE LIQUOR, CORN FLAKES AND DRY-ROASTED PISTACHIOS

ABSTRACT:
Low-moisture foods (LMFs) are increasingly implicated in foodborne illness outbreaks and recalls. LMFs inhibit Listeria monocytogenes growth but support its long-term survival which presents a public health concern. In this study, the survival and virulence of L. monocytogenes was assessed during storage for 336+ days at 4°C and 23°C on chocolate liquor (CL), corn flakes (CF) and dry-roasted pistachios (DrP). At 4°C, L. monocytogenes concentrations declined significantly on the CL and CF (≤ 0.06 log CFU/g/mth; P < 0.01), but remained stable on the DrP for at least 336 days. At 23°C, L. monocytogenes declines occurred on the CL, CF and DrP at initial rates of 0.84, 0.88 and 0.32 log CFU/g/mth, respectively. These declines may be i) strain specific and ii) attributed to cellular inactivation and transition to a viable-but-non-culturable state. Surviving cells, specifically after 4°C storage, remain infectious and capable of intracellular replication within the Caco-2 enterocyte model.