Which foods are at highest risk for Listeria contamination and why?

• A. Ready-to-eat deli meats, soft cheeses, unpasteurized dairy; Listeria can grow at refrigeration temperatures.
• B. Fresh fruits and vegetables; Listeria cannot grow at refrigeration temperatures.
• C. Canned foods; Listeria thrives in sealed containers.
• D. Dry grains; Listeria grows in low moisture.

Answer: (A)

Listeria can grow at refrigeration temperatures, which is unusual for many other pathogens. This means foods that are eaten without further cooking and that can be stored in the fridge for a while are most dangerous if contaminated. Ready-to-eat deli meats and soft cheeses, especially those made from unpasteurized milk, fit this scenario: they may carry Listeria and, because they’re often eaten cold or lightly heated, the bacteria can multiply in the fridge. Unpasteurized dairy is risky because pasteurization normally kills Listeria, so contaminating organisms can survive in the final product. In contrast, fresh fruits and vegetables can be contaminated but aren’t as prone to active growth in the fridge, canned foods have been heat-sterilized, and dry grains have low moisture, which slows or stops Listeria growth. So the foods identified as highest risk are ready-to-eat deli meats, soft cheeses, and unpasteurized dairy. When handling these, reheat deli meats to steaming hot and avoid unpasteurized dairy to reduce the risk.