Presence of Listeria monocytogenes in hydroponic controlled environment agriculture (CEA): Contamination transfer in indoor production

Controlled environment agriculture (CEA) presents unique food safety challenges, requiring a clear understanding of pathogen occurrence, survival, and persistence. This study assessed the prevalence of Listeria monocytogenes in a commercial hydroponic CEA facility using the nutrient film technique (NFT) for pak choi cultivation. Environmental monitoring was conducted at three time points (EM1, EM2 and EM3) over 8 months, with 156 samples collected, focusing on food contact surfaces and non-food contact surfaces, including the crop and water. L. monocytogenes was detected in EM1 on the boot covers used for walking through preharvest, harvest, and postharvest areas, demonstrating the effectiveness of this sampling tool. Another positive detection was found in the drainage nutrient solution in EM1, indicating a potential contamination risk to the crop. However, the cleaning and sanitation strategy implemented after EM1 was effective, as no L. monocytogenes was detected in the subsequent monitoring samplings (EM2 and EM3) despite an increased number of samples. A simulated contamination transfer of L. innocua in a CEA facility, mimicking contamination from a puddle and transfer via worker boots and equipment wheels, showed initial viability (T0); however, after 24 h, viable cells were recovered from only a few floor steps. Our key findings indicate that CEA floor surfaces can serve as vectors of microbial contamination and that recirculated nutrient solutions in hydroponic systems represent potential risks of pathogen spread. This study underscores the importance of comprehensive environmental monitoring and targeted cleaning and sanitizing practices to minimize contamination risks in hydroponic CEA systems. • Low occurrence of L. monocytogenes was detected in hydroponic pak choi CEA (2 out of 156 samples). • L. monocytogenes was identified and sequenced on boot swabs and in drainage nutrient solution. • Boot swabs sampled large surface areas and assessed cleaning efficacy. • Elevated temperatures reduced the viability of L. innocua transferred to the CEA floor via boots and wheels.