Internalization assessment of E. coli O157:H7 in hydroponically grown lettuce

Abstract

Hydroponics and aquaponics have been gaining popularity to grow produce. Escherichia coli O157:H7 may internalize within edible produce. This study was to investigate E. coli O157:H7 internalization in red sails lettuce in a custom designed/constructed model hydroponic system under laboratory-controlled conditions. The objective was to determine not only the likelihood and level of internalization within hydroponically-grown lettuce but also potentially facilitated internalization with injured lettuce roots. The hydroponic tank was contaminated with Escherichia coli O157:H7 (E. coli) at 5-log CFU/mL. Roots of randomly selected plants were damaged by cutting either two- or three-times (two experimental treatment groups). Experimental control did not have root damage. Following lettuce harvest and surface decontamination, E. coli was enumerated on 3-M petrifilm™ EC. Internalized E. coli was detected at 2.4 ± 0.7, 4.0 ± 1.9, and 3.3 ± 1.3 log CFU/g in control, lettuce with two-, and three-cuts to their roots, respectively. Root injury showed a trend (p > 0.05) towards increasing E. coli internalization. Two-vs. three-cuts to roots did not (p > 0.05) affect E. coli internalization, although it showed 0.9-log CFU/g of a numerical difference. The highest level of internalized E. coli was detected at 4.7 log CFU/g in a lettuce plant that received two cuts to its root system.