Life Cycle

1. Listeria is found in contaminated food.

2. The listeria bacteria is ingested.

3. The bacteria leaves the digestive system and infects the cells in the epithelial lining.

4. The macrophages (cells that aid in removing dead cells and bacteria) in the immune system try to attack and destroy the bacteria through phagocytosis (when the cell engulfs bacteria and digest the bacteria in order to get rid of it).

5. The listeria bacteria is able to get into the cytoplasm and dodge the macrophages because of the enzymes it creates. This enzyme/protien is called listeriolysin O, it is secreted into the macrophages vacuole which damages the macrophages. 

6. Through binary fission, the bacteria is able to reproduce asexually and create identical listeria bacteria in the host cell's cytoplasm.

7. The bacteria use the protein of the host cell to create an actin (a protein found in epithelial and muscle cells) tail in order to transport itself throughout the cells cytoplasm. It uses the tail to propel itself for travel.

8. It creates a filopod (projections of cytoplasm ) by pushing against the cell's outer membrane.

9. It leaves the host cell when the cell comes in contact with a neighbouring cell. It moves into the  neighbouring cell where it repeats the process.

Illistration showing the process of the listeria life cycle.
Shows entering the cell's cytoplasm, binary fission, and leaving the cell's cytoplasm to a neighboring cell
and restarting the process.
From http://www.jhu.edu/cmml/emph_ListSteps.html