Salmonella typhimurium can infect plants

Salmonellosis is one of the most common types of food poisoning.  Caused by bacteria from the genus Salmonella, every year it affects millions of people throughout the world.  Until now, it was accepted that human beings contracted this infection by consuming contaminated products of animal origin (meat, eggs, milk) or other foods, such as vegetables, that had been contaminated by manure.  Salmonella are thus found throughout the food chain.

Researchers at INRA and the University of Vienna have now shown, in the model plant Arabidopsis, that the bacterium can directly infect plants.  Using molecular biology and genomic techniques, they have demonstrated that the bacterium can infect the tissues of a plant and develop inside its cells. 
The scientists have shown that plants perceive an infection by Salmonella and activate their immune system, but this is not sufficient to block the entry of bacteria into their cells, where they proliferate.  This occurs very rapidly during the early days of the infection, but the symptoms of the disease only appear two weeks later.  The plants becomes chlorotic and start to die. 
The teams also tested mutants of Arabidopsis with a deficient immune system.  After infection by Salmonella, the mutants were more susceptible and died much earlier than wild-type Arabidopsis.  An analysis of plant defences at the molecular level showed that the plants and bacteria were really in a state of war, and ultimately it was always the bacteria that won the battle. 
These results suggest that bacteria probably use a battery of virulence factors to suppress the plant's immune defences.  This Arabidopsis-Salmonella model system could be of considerable value to determining new targets and thus developing novel treatments to combat the diseases caused by bacterial infections in humans.