Inactivation with UV-radiation and internalization assessment of coliforms and Escherichia coli in aquaponically grown lettuce

Escherichia coli O 157:H7 can internalize in produce. Therefore, a food safety risk exists for lettuce grown using mixed water sources such as aquaponics, which combines aquaculture with hydroponics. Objectives were to determine antimicrobial efficacy of UV-radiation on reduction of E. coli/coliform in a pilot-scale demonstration aquaponic system and assessment for possibility of E. coli/coliform internalization in aquaponically-grown lettuce. Water from aquaculture and hydroponic was sampled for 6 weeks prior to lettuce harvest. Water and lettuce samples were spread-plated on 3-M petrifilm (TM) EC (E. coii/coliform) and on m-Endo agar. The average bacterial counts in aquaculture raceways were approximately 10(2) CFU/ml and 10(4) CFU/L on 3-M petrifilm and m-Endo agar, respectively. Bacterial counts did not (p > 0.05) increase in the aquaculture raceways or hydroponic greenhouse, suggesting that neither fish nor plants contributed to bacterial growth. The coliform bacteria detected in the aquaponic system reflected their normal presence in the environment where the aquaponic system was located. UV treatment reduced (p < 0.05) bacterial counts by approximately 1.5 and 3.0-log on 3-M petrifilm and m-Endo agar, respectively. Internalized coliforms or E. coil were not detected in lettuce. This study demonstrates the effectiveness of coliform inactivation by UV-radiation in a pilot-scale real-life aquaponic system.