Lettuce (Lactuca spp.) is one of few edible plant species that produce latex. During lettuce harvest, latex leaks from ruptured laticifers onto the cut stem and adheres to other lettuce heads, harvesting tools, and packaging. Little is known about the colonization of lettuce latex by Shiga toxin-producing E. coli O157:H7 (EcO157), the main causal agent of outbreaks linked to lettuce. We screened 14 lettuce genotypes, including wild lettuce and commercial morphological types, for EcO157 multiplication in their latex-coated cut stems. Change in EcO157 density after its inoculation into the latex of these genotypes differed significantly and ranged from a 1.7× decline to a 3.6× increase over 6 h at 25 °C. EcO157 density increased in all genotypes except one, a romaine lettuce breeding line that caused decline of the pathogen. Latex biochemical properties, such as concentration of sucrose, glucose, fructose, phenolic compounds and H