Utah Food Safety Practice Test

Unpasteurized cheese was kept in a refrigerator for 20 days. What organism might you expect to have caused foodborne illness?

1. Salmonella

2. Listeria monocytogenes

3. E. coli

4. Clostridium botulinum

The correct answer is: Listeria monocytogenes

Unpasteurized cheese is particularly susceptible to contamination by Listeria monocytogenes, a pathogenic bacterium. This organism is known for its ability to thrive even in refrigerated environments, which is a significant factor in why unpasteurized dairy products can pose a risk of foodborne illness. Listeria can multiply at refrigeration temperatures, allowing it to persist in food products for extended periods, such as the 20 days noted in this scenario. This persistence increases the risk of infection, especially in vulnerable populations such as pregnant women, the elderly, or individuals with weakened immune systems. Salmonella and E. coli are more commonly associated with raw meats and contaminated vegetables, while Clostridium botulinum typically thrives in low-oxygen environments and is less likely to be a concern in refrigerated dairy products like cheese. Therefore, when considering the specific context of unpasteurized cheese stored in a refrigerator, Listeria monocytogenes is the most likely candidate for foodborne illness.