Role of Seed Contamination in the Persistence and Transmission of Listeria monocytogenes in Daikon Microgreens

Introduction:

Microgreens, young edible seedlings harvested at the cotyledon stage, are highly valued for their nutritional content and growing popularity as a health-conscious food. However, like sprouts, their consumption without further processing poses a food safety concern due to potential microbial contamination. This study evaluates the persistence and transmission of Listeria monocytogenes (LM) in daikon microgreens grown on a soil-free biostrate pad following seed contamination.

Methods:

Daikon seeds were spray-inoculated with a four-strain LM cocktail to achieve ~3 log CFU/g. After overnight drying, seeds were cultivated on soil-free biostrate pads for 10 days. Samples from microgreens, biostrate pads, and irrigation water were collected on days 0, 3, 7, and 10 for LM enumeration using modified Oxford agar. Data were analyzed using GraphPad Prism, with significance set at P ≤ 0.05.

Results:

LM populations increased from ~3 log CFU/g in seeds to ~6 log CFU/g in microgreens within 3 days. Similar levels were detected on the biostrate pad and in irrigation water. LM levels remained stable up to day 7 but declined by ~1.5 log CFU/g in microgreens and water by day 10. No significant change in LM levels was observed on the biostrate pad between days 3 and 7. Significant differences in LM populations were noted in microgreens and water between days 3 and 7 (P < 0.05).

Conclusion:

Seed contamination with LM can lead to significant pathogen proliferation and persistence in both edible microgreens and the production environment. These findings highlight the need for effective seed decontamination strategies to reduce cross-contamination risks during microgreen production and improve food safety.