Monday, November 13, 2006

Manure and Contaminated Irrigation Water as Vehicles of E. coli Transmission to Fresh Produces.

Mussie Habteselassie1, Marianne Bischoff1, Bradley L. Reuhs2, Bruce Applegate3, and Ronald Turco1. (1) Purdue Univ, Dept of Agronomy, 915 W. State St, West Lafayette, IN 47907, (2) Purdue University, Dep't of Food Science, 745 Ag. Mall Drive, West Lafayette, IN 47907, (3) Purdue University, Department of Food Science, 745 Agriculture Mall Drive, West Lafayette, IN 47907-2009

Several outbreaks of human infections by E. coli 0157:H7 have been reported as a result of consumption of raw vegetables and fruits. The role that applications of animal waste and contaminated irrigation water play as sources for bacterial transfer is not clear. The objective of this study was to understand the factors controlling the transmission of E. coli from soil and irrigation water to produces. We are taking advantage of E. coli strains modified with gfp and lux insertions in order to understand the relationship.  Radish and lettuce were grown in soil inoculated with E. coli (106 cells g-1 or mL-1), 1) through uniform distribution in the soil (ES), 2) via manure (EM), and 3) via irrigation water (EI). The phyllosphere, rhizosphere and bulk soil were periodically sampled and analyzed for E. coli with plate count and real-time PCR. Because of the gfp and lux insertions, the internalization of E. coli was also investigated. EI treatment after seeding was the most effective vehicle of transmission as it moistened the seeds, creating maximum contact with E. coli. E. coli plate counts on radish phyllosphere after 7 days of germination were 6.7, 2.2 and 2.0*103 cfu g-1 for EI, ES and EM treatments, respectively.  The highest number of E. coli was associated with the rhizosphere due to increased availability of carbon from exudates. Images of bioluminescent E. coli cells were captured with a CCD camera on leaves and root surfaces, showing the exact locations of contamination. We are currently refining the methods we used to investigate the internalization of E. coli. As E. coli has a very low infective dose, our results highlight the risk associated with field application of manure and contaminated irrigation water for vegetable growth and the importance of  following proper guidelines to avoid possible human infections.

Handout (.pdf format, 406.0 kb)