Lettuce Genotype-Dependent Effects of Temperature on Escherichia coli O157:H7 Persistence and Plant Head Growth.

ABSTRACT

Lettuce has been commonly associated with the contamination of human pathogens, such as Escherichia coli O157H7 (hereafter O157H7), which has resulted in serious foodborne illnesses. Contamination events may happen throughout the farm-to-fork chain, when O157H7 colonizes edible tissues and closely interacts with the plant. Environmental conditions have a significant impact on many plant-microbe interactions; however, it is currently unknown whether temperature affects O157H7 colonization of the lettuce phyllosphere. In this study, we investigated the relationship between elevated growth temperatures, O157H7 persistence, and lettuce head growth using 25 lettuce genotypes. Plants were grown under optimal or elevated temperatures for 3.5 weeks before being inoculated with O157H7. The bacterial population size in the phyllosphere and lettuce head area was estimated at 0- and 10-days postinoculation (DPI) to assess bacterial persistence and head growth during contamination. We found that growing temperature can have a positive, negative, or no effect on O157H7 persistence depending on the lettuce genotype. Furthermore, temperature had a greater effect on head area size than the presence of O157H7. The results suggested that the combination of plant genotype and temperature level is an important factor for O157H7 colonization of lettuce and the possibility to combine desirable food safety traits with heat tolerance into the lettuce germplasm.