A microscopic view of label-free and living Listeria bacteria

What is Listeria and where does it come from?

Infection from Listeria monocytogenes is a food borne bacterial illness that can be very serious for pregnant women and people with impaired immune systems. Listeria infection can be contracted by eating badly preserved meat and unpasteurized milk products (including soft cheese, ice cream, and yogurt).

Healthy individuals are normally resistant to listeria infection, but the disease can be fatal to unborn babies and very young babies. Immunodepressed people also are at higher risk. Listeria bacteria is very resistant and can survive refrigeration and even freezing. This is why people at risk should just avoid consuming products at risk.

Mouse macrophages infected with Listeria

In this video we observe mouse macrophages that have been infected with Listeria monocytogenes.

At the beginning of the video, the cell at the top of the field of view is going through mitosis. The chromosomes’ condensation is clearly observable in the center of the cell. Listeria bacteria are observable in this same host cell: they are either free to move around in the cytoplasm or inside cytoplasmic vacuoles, replicating. When the host cell divides, we can observe the transmission of these pathogenic bacteria to the daughter cells.

In the second part of the video, we move the attention to the cell below. At the end of its reproductive cell cycle, the Listeria bacterium is released through the host cell’s plasma membrane and is free to infect other cells. Here we clearly see the vacuole localization of Listeria followed by membrane destruction and cell death during its release.