Persistence of foodborne bacterial pathogens on microgreens and soil irrigated with contaminated water

Authors: RAO, AISHWARYA - University Of Maryland; PRADHAN, ABANI - University Of Maryland; Patel, Jitendra

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2025
Publication Date: 8/5/2025
Citation: Rao, A.P., Pradhan, A.K., Patel, J.R. 2025. Persistence of foodborne bacterial pathogens on microgreens and soil irrigated with contaminated water. Journal of Food Protection. 88(10). Article 100594. https://doi.org/10.1016/j.jfp.2025.100594.
DOI: https://doi.org/10.1016/j.jfp.2025.100594

Interpretive Summary: Consumption of microgreens has increased due to their health benefits. Humid environmental conditions used for growing microgreens make them susceptible to contamination with disease-causing bacteria. Further, there is no treatment after harvest to kill contaminated bacteria from microgreens. We investigated transfer and persistence of bacterial pathogens from two types of contaminated irrigation waters (municipal water and rainwater) to four microgreens (broccoli, mustard, red cabbage, daikon). All three pathogens, Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes, were transferred from contaminated irrigation waters to microgreens; however, their populations decreased gradually from day 7 to day 14, at the time of harvest. The source of irrigation water affected the persistence of pathogens. Salmonella and E. coli O157:H7 persisted in lower numbers when contaminated with rainwater. Pathogens were also found in soil used for growing microgreens. These findings suggest stringent requirements for microbial quality of irrigation waters to prevent contamination of microgreens with pathogens. The information is useful to U.S. fresh produce growers to reduce food safety risks.

Technical Abstract: Microgreens, like leafy greens, are susceptible to contamination at the pre-harvest stage, posing food safety concerns, particularly as their consumption rises due to their recognized bioactive benefits. Recalls associated with microgreens have further underscored these concerns. This study aimed to investigate the potential transfer of enteric pathogens to microgreens irrigated with contaminated water. Municipal water (MW) and rainwater (RW) inoculated with low and high concentrations of Salmonella enterica, Escherichia coli O157:H7, or Listeria monocytogenes were used to irrigate daikon, red cabbage, broccoli, and mustard microgreens cultivated on soil beds. Microgreen and soil samples were collected on days 7 and 14 and analyzed using most probable number (MPN) enumeration or spiral plating on selective media. Significant variations in pathogen recovery were observed across days 7 and 14, irrespective of microgreen variety or water source. When irrigated with Salmonella contaminated-RW at ~5 Log CFU/ml, broccoli, daikon, and red cabbage exhibited a significant reduction in pathogen levels by day 14. Similarly, daikon, mustard, and red cabbage irrigated with Listeria contaminated MW demonstrated significant pathogen population changes over the 14-day period. Similar trends were observed for E. coli O157:H7 in daikon and red cabbage irrigated with rainwater. Salmonella and E. coli O157:H7 persisted in lower numbers on microgreens when contaminated with rainwater. These findings highlight the potential for transfer of enteric pathogens from contaminated irrigation water to the edible portions of microgreens, emphasizing the importance of rigorous microbial quality control of irrigation water in controlled environment agriculture to mitigate contamination risks.