Survival of Escherichia coli on strawberries grown under greenhouse conditions

Abstract

Strawberries are soft fruit that are not recommended to have a post-harvest wash due to quality concerns. Escherichia coli O157:H7 has been linked to outbreaks with strawberries but little is known about the survival of E. coli during the growth cycle of strawberries. The survival of E. coli on strawberry plants during growing under greenhouses conditions was evaluated. Soil, leaves, and strawberries (if present) were artificially contaminated with an E. coli surrogate either at the time of planting, first runner removal (4 wk), second runner removal (8 wk), or one week prior to harvest. At harvest E. coli was recovered from the leaves, soil, and strawberries regardless of the contamination time. Time of contamination influenced (P < 0.05) numbers of viable E. coli on the plant. The highest survival of E. coli (P < 0.0001) was detected in soil that was contaminated at planting (4.27 log10 CFU g soil(-1)), whereas, the survival of E. coli was maximal at later contamination times (8 wk and 1 wk prior to harvest) for the leaves (4.40 and 4.68 log10 CFU g leaves(-1)) and strawberries (3.37 and 3.53 log10 CFU strawberry(-1)). Cross contamination from leaves to fruit was observed during this study, with the presence of E. coli on strawberries which had not been present at the time of contamination. These results indicate that good agricultural best practices to avoid contamination are necessary to minimize the risk of contamination of these popular fruit with enteric pathogens. Practices should include soil testing prior to harvest and avoiding contamination of the leaves.

Keywords: Escherichia coli; Pre-harvest; Strawberries; Survival.