Listeria monocytogenes is a Gram-positive bacterium that is very common in soil, water, plants, food, sewage. Listeria is the cause of a rare food-borne disease that is highly lethal.

About 25% of the people who contract listeriosis die of it. Although most Listeria bacteria are destroyed by the immune system when they enter the body. Those that escape often evade the immune system because they travel from cell to cell without using the circulatory systems.

A big problem in dealing with Listeria, is that this bacterium is very hardy, and that it is able to grow in temperatures from 4°C (fridge temperature) to 37°C (body temperature). Because of that, even miniscule amounts that remain after production can grow out during refrigeration to potentially deadly numbers. As a result, this bacterium is one of the scourges of the food industry, and the cause of many expensive recalls.

The negative result of these recalls is that the public often gets the impression that food quality is going down, whereas the opposite is true. Food poisonings are becoming so rare that they are now newsworthy. Just a few decades ago, food poisonings were so common that they were hardly ever mentioned in the media.

The fact that we have food recalls is not a sign of a badly working food distribution, it is a sign that the system is becoming better at detecting ever smaller contaminations.

In 2008, Listeria was responsible for several deaths because a single production line in a single Toronto plant of Maple Leaf Foods was contaminated, a contamination that was only found after a systematic dismantling of the entire production line.