Light may help bacteria invade produce

Researchers from Tel Aviv University and Israel's Agricultural Research Organization said such internalization would make disease-causing bacteria impervious to washing.

In the study, researchers examined the role light and photosynthesis might play on the ability of salmonella bacteria to infiltrate lettuce leaves via stomata -- small pores through which gases and water vapor can pass.

Sterile iceberg lettuce leaves were exposed to bacteria either in the light, in the dark or in the dark after 30 minutes of exposure to light. The scientists said they found incubation in the light or pre-exposure to light resulted in aggregation of bacteria around open stomata and invasion into the inner leaf tissue. In contrast, incubation in the dark resulted in a scattered attachment pattern and very little internalization.

"The elucidation of the mechanism by which salmonella invades intact leaves has important implications for both pre- and post-harvest handling of lettuce and probably other leafy vegetables," the scientists said. "The capacity to inhibit internalization should limit bacterial colonization … and consequently might enhance the effectiveness of surface sanitizers."

The study is reported in the October issue of the journal Applied and Environmental Microbiology.

Copyright 2009 by United Press International.