Can’t wash e-coli

The role of the plant’s pores in defense against invading bacteria has been redefined by a new look at the behavior of one the plant’s first lines of defense against disease.

Pores called stomata are like tiny mouths that open and close during photosynthesis, exchanging gases. In sunshine, the stomata open. In darkness, they close to conserve water.

It has been assumed that these tiny ports were busy with their photosynthesis business and were merely unwitting doorways to invading bacteria but recent discoveries show that stomata are an intricate part of the plant’s immune system that can sense danger and respond by shutting down.

It appears those plant-based bacteria produce a phytotoxin, a chemical called coronatine, to force the pores back open. For bacteria, entry is crucial to causing disease and probably survival. They could die if left lingering on the surface. Animal-based bacteria do not produce coronatine.

“Now that we know a key step in bacteria’s attack, we have something we can learn to interfere with,” Melotto said. “From this we can learn about disease resistance.”

Conventional wisdom holds that harmful bacteria on fruits and vegetables are the remnants of contamination skulking on the exterior of the plants — easily washed away by conventional surface sterilization techniques. But University of Florida microbiology experts believe the recent rash of spinach-related E. coli infections may be instead linked to swarms of the pathogen lurking inside the leafy greens.

“We know that plants can take bacteria up from the soil through their roots,” Triplett said. “What we need to do now is investigate whether this is a problem with our crops, and then what we can do about it if it is.”

For food safety experts, this could mean a paradigm shift in thought about food sterilization.

“When I was a graduate student, we were taught that the insides of plants were sterile,” said Michael Doyle, director of the Center for Food Safety at the University of Georgia. “Further elucidation is needed before we can say this is a major health concern…but assuming E. coli is getting into the plant — yes, this will be a big problem to address.”

The problem, UF researchers say, would be twofold. The first is the question of how to keep dangerous bacteria out of water and soil in the first place. The second is how to eliminate a pathogen if it does infiltrate crops. [story]