Inactivation by UV-Radiation and Internalization of Coliforms and Escherichia coli in Aquaponically and Hydroponically Grown Lettuce

Recent studies have shown that coliform bacteria, specifically Escherichia coli O157:H7, can internalize in leafy green produce. Therefore, a risk exists for lettuce being grown in systems using mixed water sources. Additionally, Ultra Violet light radiation has been shown to inactivate coliforms in water. For this reason, an experiment was conducted at West Virginia University\u27s aquaculture facility to determine the effect of UV-radiation in water supplying an aquaponic channel with nutrients, and to assess the risk of coliform and E. coli internalization. In this experiment, the spring fed, flow-through aquaponic system was receiving runoff from cattle pastures as a source of coliform bacteria. An inline UV-light system was randomized to treat water going to half of the hydroponic channels growing lettuce downstream from the raceways containing fish. Water going into and leaving the eight channels was sampled for 6 weeks in addition to the upstream water (before and after the fish raceways). Additionally, lettuce samples were aseptically collected during the time of harvest. Water samples were plated directly on 3-M Petrifilm EC (E. coli/ coliform) as well as on M-endo agar using a membrane filter. Incubation was done at 35°C for 48h for both media. Lettuce samples were surface sanitized, homogenized, and directly plated on M-endo agar. The mean coliform count of all untreated water was 1.93 x 101 CFU/ml. A 3-4 Log reduction in total coliforms for treated water entering the channels was observed. There were no detectable levels of E. coli in the treated water entering the channels; the mean concentration of untreated water was 0.69 CFU/ml. Additionally, internalized coliforms were not detected in the lettuce samples. Although, black colonies did grow on the media, they tested negative in a confirmation test; discoloration was most likely due to the decomposition of the lettuce particles within the samples. This study demonstrates the effectiveness of coliform inactivation by UV-radiation in water and suggests that coliform/E. coli internalization in lettuce may be a conditional phenomenon.;In efforts to verify the possibility of internalization in lettuce grown in water, as well as its dependence on conditional factors, a follow-up study was conducted at West Virginia University. The objective of this study was to determine the level in which internalization of E. coli occurs in lettuce as well as the effect plant root injury may have on it within a hydroponic system. A hydroponic system was set up to grow lettuce in water inoculated with Escherichia coli O157:H7. The inoculated water was kept at a concentration around 105 CFU/ml of E. coli O157:H7 for the duration of this study. Half of the plants were randomized to receive 3 consecutive treatments of damage to the root tips. Edible portions of the lettuce were then harvested to be analyzed. The lettuce was surface-sanitized, homogenized, and filtered using a bag mixer. Sample dilutions were prepared and inoculated on 3-M Petrifilm EC. Internalization was observed at a mean of 1.66 x 101 CFU/g in both treated and untreated plants and as high as 4.90 x 104 CFU/g in one treated sample. Although there was no significant difference between treatment and the control, it should be stated a difference was observed. Taking into account the sample size used, significance may be seen if this were repeated on a larger scale. The variation within the samples may also suggest other contingent conditions may be a factor