Seminar Series Abstract

Gamma Irradiation and Aqueous Chlorine Interventions to Control E. coli O157:H7/GFP Internalized in Lettuce Grown in a Hydroponic System

Agnes Kilonzo-Nthenge

Institute of Agricultural and Environmental Research Seminar Series
Tennessee State University, Nashville, TN
March 3, 2004

The purpose of this study was to evaluate the uptake and transmission of E. coli O157:H7/pGFP in lettuce plants and to determine the viability of internalized E. coli O157:H7/pGFP in lettuce tissue after gamma irradiation and aqueous chlorine treatments. Lettuce seedlings were grown in a hydroponic system artificially contaminated with 10³, 10⁵ or 10⁷ CFU of E. coli O157:H7 per ml. Plants were sampled over at 3, 7, and 14 day period and subjected to very low doses of gamma irradiation at 0.25, 0.5, 0.75 kGy and aqueous chlorine at 200 ppm.

E. coli O157:H7/pGFP was located in the inner tissue of lettuce leaves and the association of E. coli O157:H7/pGFP cells with lettuce roots was dose dependent as demonstrated by Confocal laser scanning microscopy. Gamma irradiation at 0.25, 0.5 kGy  and  aqueous chlorine treatment at 200 ppm for 10 min, failed to eliminate E. coli O157:H7/pGFP cells in the internal location of lettuce tissue. Only irradiation at a dose of 0.75 kGy reduced E. coli O157:H7/pGFP cells to non-detectable levels.  The results suggest that E. coli O157:H7/pGFP migrated from the artificially contaminated hydroponic system to the internal locations of lettuce tissue and therefore, protected from the action of aqueous chlorine due to its inaccessibility. Gamma irradiation proved to be more efficacious than aqueous chlorine in eliminating E. coli O157:H7/pGFP internalized in lettuce tissue.

Since the current production methods cannot ensure safe raw fruits and vegetables free of pathogenic bacteria, irradiation should be used as a tool at critical control point (CCP). This will ensure the safety of fresh produce before its distribution to consumers. However, irradiation technology to be fully harnessed, there must be an effort to educate consumers about the potential benefits of this great tool.

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