Effect of pH, Nutrient Composition, and UV-C Light Treatment on Listeria monocytogenes in Hydroponic Nutrient Solutions

Hydroponic nutrient solutions may create favorable conditions for the growth of environmental pathogens such as L. monocytogenes. This study evaluated the growth and survival of L. monocytogenes in distilled water and tomato, lettuce, and strawberry nutrient solutions at pH 5, 6, and 7 over 72 h, and assessed the effectiveness of UV-C treatment (1.32 mW/cm²) for microbial reduction. Distilled water at pH 5 supported limited survival, with counts decreasing from 2.96 to 2.20 log CFU/mL (p ≤ 0.05). In tomato solutions, L. monocytogenes levels showed minimal change, while lettuce and strawberry solutions supported significant growth, particularly at pH 6, indicating that both pH and nutrient composition influence pathogen behavior. UV-C treatment significantly (p ≤ 0.05) reduced L. monocytogenes across all nutrient solutions with greater reduction observed at longer exposure times. In lettuce solutions, 5, 10, and 15 s exposures decreased populations from 5.70 log CFU/mL to 4.61, 2.26, and 1.38 log CFU/mL, respectively, with similar reductions in tomato (to 4.49, 2.14, and 1.04 log CFU/mL) and strawberry solutions (to 4.50, 2.19, and 1.75 log CFU/mL). These results demonstrate that hydroponic solutions can facilitate L. monocytogenes survival depending on pH and nutrient content. While UV-C offers a promising intervention strategy, further work is needed to optimize decontamination approaches for hydroponic food production systems.