Human body's defence mechanism kills salmonella bacteria

Researchers from the Goethe University have found the mechanism through which body cells recognise salmonella bacteria and render it harmless.

The human defense system manages to digest invading bacteria, which is why a healthy human being will only fall ill if he consumes more than 100.000 salmonella bacteria via contaminated food source, such as eggs or meat.

Salmonella infection is known to begin with bacteria entering the epithelial cells of the intestinal mucosa. To prevent them from multiplying, special cell organelles called autophagosomes are activated.

These encircle the invaders and then become absorbed in other organelles called lysosomes containing certain special digestive enzymes, which break down the bacteria into their constituent parts.

However, the study explains how autophagosomes recognise salmonella bacteria.

The salmonella are marked as 'waste material' by the molecule ubiquitin. For the autophagosomes to become active, the marked bacteria have to bind to another molecule "LC3" on the autophagosomal membrane.

Here, the protein optineurin links the marked Salmonella to the autophagosmal LC3, thereby setting off a process of selective autophagy.

"We suspect that phosphorylation acts as a regulated switch to trigger selective autophagy of bacteria but might also prove significant in other cargoes like protein aggregates or damaged mitochondria," said Prof. Ivan Dikic from the Goethe University in Frankfurt.

The study appears in the scientific journal "Science".