How low temperature is attained in a refrigerator?

The FDA says on their website to keep the refrigerator set below forty degrees Fahrenheit. "Keeping the refrigerator at 40°F or below is important because - unlike most foodborne bacteria - Listeria will grow in the refrigerator, and it will grow faster at refrigerator temperatures above 40°F. And, the longer ready-to-eat, refrigerated foods are stored in the refrigerator, the more time Listeria has to grow. Finally, Listeria can spread from one food to another through spills in the refrigerator. That's why keeping the refrigerator clean is also important!"