Food-safety experts have long believed that Salmonella bacteria could only enter tomatoes through wounds in the stem or fruit — but a new University of Florida laboratory study shows it can also happen another way.

Plant pathologist Ariena van Bruggen, a professor in UF’s Institute of Food and Agricultural Sciences, has published a paper in the online journal PLoS One, with research findings that show — for the first time — that Salmonella can enter tomato plants through intact leaves, travel through the plant and end up in the fruit itself.

But she says she can’t stress enough that it isn’t at all easy for it to happen, even in the lab, and would be unlikely under field conditions.

“The message is that yes, (Salmonella) can be internalized in tomato, but it’s rare — the chance is so low,” she said. “I would tell consumers not to worry too much.”

Although van Bruggen, a member of UF’s Emerging Pathogens Institute, described her experiment as a “worst-case scenario,” she said the findings suggest tomato growers and packers should continue to review their already-stringent safety standards, taking a look at factors such as irrigation water sources, the possibility of wild animals getting too close to plants and the use of surfactants.

Keith Schneider, a food safety expert and IFAS faculty member, called the study’s findings intriguing, but said hand-washing by consumers and food handlers is still likely to have the single biggest impact on whether people become ill from anything they eat.

“There is probably a far bigger risk of people becoming sick from not washing their hands, or their kids not washing their hands, than the possibility of this route of infection occurring in nature,” he said.