Bugs can enter and grow in fresh veggies: washing is not enough
Posted: May 28th, 2008 - 10:50am by Doug PowellResearchers in Austria and France report today that Salmonella can infect plant cells and successfully evade all the defence mechanisms of plants, meaning that cleaning the surfaces of raw fruits and vegetables is not sufficient to protect against food poisoning.
Work carried out by a team led by geneticist Prof. Heribert Hirt, and published today in PloS ONE, shows that the strain of bacteria known as Salmonella typhimurium can also invade, and multiply inside, plant cells. It is already known that Salmonella can survive for up to 900 days in contaminated soils, which creates a rich source of infection for plant material. However, Prof. Hirt's team can now show that bacteria from such a source can actively achieve the infection of plant cells, thereby disproving the previous assumption that infection was coincidental and - as regards the bacteria - passive.
"We marked individual bacteria with a fluorescent protein, which enabled us to observe them as they quite clearly penetrated root cells and multiplied. Just three hours after the bacteria came into contact with the roots, they had penetrated inside the cells of the finest root hairs. 17 hours later, the cells inside of the roots had also become infected. …
"The defence mechanisms fail completely. Although regulating proteins such as the two mitogen-activated protein kinases 3 and 6 are activated just 15 minutes after Salmonella has infected the plant, they cannot prevent the bacteria from multiplying. Another defence mechanism, which is activated by the plant messengers salicylic acid, jasmonic acid and ethylene, proves similarly ineffective. Although these messengers are important to coregraph the plant defense responses, they too are unable to halt the infection."
Previous work has shown that pathogens can enter the inside of tomatoes, leafy greens and cantaloupe. The current work once again demonstrates that food safety begins on the farm, and that food safety messages to cook, clean, chill and separate are seriously deficient. To quote again from the press release,
"If, as has now been discovered, Salmonella survives and multiplies in plant cells, then washing raw fruit and vegetables does nothing to prevent food poisoning."