High-Temperature Short-Time Pasteurization Inactivates Listeria monocytogenes.

Area of Science:

• Food Microbiology
• Dairy Science
• Bacterial Pathogenesis

Background:

• Listeria monocytogenes is a significant foodborne pathogen.
• Bovine phagocytes can harbor Listeria monocytogenes.
• Effective pasteurization is crucial for dairy product safety.

Purpose of the Study:

• To evaluate the efficacy of commercial pasteurization against Listeria monocytogenes.
• To determine if Listeria monocytogenes protected within bovine phagocytes is inactivated by pasteurization.
• To compare the sensitivity of different Listeria monocytogenes detection methods post-pasteurization.

Main Methods:

• Commercial-scale pasteurization (72-73°C, 15-16 s) of raw milk inoculated with Listeria monocytogenes Scott A.
• Listeria monocytogenes introduced freely suspended, within bovine phagocytes (in vitro), and within bovine phagocytes in infected cows (in vivo).
• Assay methods included cold enrichment, selective enrichment (FDA and USDA-FSIS), and direct incubation of large volume samples.

Main Results:

• No Listeria monocytogenes were detected in pasteurized milk using any of the four applied assay methods.
• Commercial thermal processing demonstrated complete inactivation of Listeria monocytogenes under tested conditions.
• The protective effect of bovine phagocytes did not prevent Listeria monocytogenes inactivation by pasteurization.

Conclusions:

• Commercial pasteurization is highly effective in eliminating Listeria monocytogenes from raw milk.
• Standard microbiological detection methods may lack sensitivity for detecting low levels of surviving Listeria post-pasteurization.
• Thermal processing provides a robust barrier against Listeria monocytogenes contamination in dairy products.