Shigella infects cells by using a secretion system to inject proteins into human cells

Scientists have found that the bacterium that causes dysentery uses a 'sword and shield' approach to cause infection.

According to research published in Science, the team from Imperial College London and Institut Pasteur, Paris, found that shigella, the bacteria which causes dysentery, is able to invade cells, while stopping any response from the immune system.

They found that shigella was able to infect cells by using a secretion system to inject proteins into human cells, (the sword), while lipopolysaccharide (LPS) on the surface of the bacteria acts as a shield to protect the dysentery bacterium from being destroyed by the body's immune system.

Dr Christoph Tang, from Imperial College London, and one of the researchers, comments: "This is the first description of bacteria able to use this 'sword and shield' approach, showing how dysentery is able to infect the body so effectively. We have shown why the bacteria can avoid being destroyed by the body's immune responses through the expression of a molecule that acts as a shield on its surface."

The researchers found that shigella, the bacteria causing dysentery uses a Type III secretion system to inject proteins into human cells. This causes the cells to become inflamed, resulting in symptoms of dysentery, such as bloody diarrhoea. At the same time, the LPS chains on the surface of the bacteria are shortened. This allows the needles to inject proteins, while protecting the bacteria from being destroyed by the immune system.

Dr Tang adds: "This discovery greatly expands our understanding of how bacteria are sometimes able to evolve although it is unlikely to result in new treatments or vaccines for dysentery. In this case, the dysentery bacteria has evolved into a highly effective and dangerous infection."