Salmonella bacteria on lettuce penetrate the leaves to enter inner tissues via stomata, while also actively swimming toward photosynthetically produced nutrients, according to Shlomo Sela and other members of an Israeli research team.
Although other bacterial plant pathogens also enter plant tissues, the Israeli experiments provide the first known evidence of bacteria responding chemotactically to photosynthetic products as part of this invasive process. Speculating that other types of bacteria similarly gain entry to leaf tissues, he suggests that measures to limit this process in leafy vegetables could improve food safety. Details of the research appear in the October Applied and Environmental Microbiology (75:6076-6086).
"Following completion of a series of attachment experiments between Salmonella and romaine lettuce, we realized that our results were different from those reported by others, who worked with iceberg lettuce," says principal investigator Sela of the Agricultural Research Organization at the Volcani Center in Bet Dagan, Israel. To probe those differences, doctoral student Yulia Kroupitski began experimenting with iceberg lettuce. One day, she and technician Eddy Belausov saw that the salmonellae were "swimming toward and disappearing inside stomata," Sela says.