Quantitative microbial risk assessment of antibiotic-resistant Salmonella enterica contaminating hydroponic leafy vegetables

Hydroponics plays an important role in addressing food security concerns, particularly in countries aiming to increase food self-sufficiency. However, it is vulnerable to microbial contamination, and biofilms formed in hydroponic facilities may promote horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). Eventually, the bacteria are internalized into the edible parts of the vegetable through the roots, which can lead to human exposure to antibiotic-resistant pathogenic bacteria. Microbial risk assessment can play a pivotal role in microbial risk management; however, it has not been conducted for hydroponic systems. In this study, a quantitative microbial risk assessment of hydroponic vegetables was performed using literature values regarding the concentration of Salmonella spp. in hydroponics, efficiency of HGT, probability and rate of internalization, vegetable consumption patterns, and dose-response relationships. Furthermore, a sensitivity analysis was performed to identify the factors that had a significant impact on the infection probability per single exposure event for all Salmonella spp. by calculating Spearman's correlation coefficients. The estimated annual probability of infection per person by all Salmonella spp. was 2.04 × 10⁻¹, while the estimated probability of infection from Salmonella spp. that acquired ARGs was 2.54 × 10⁻⁶. Our sensitivity analysis showed the correlation between the occurrence of internalization and hydroponic contamination levels, highlighting the need for increased awareness and regulatory action.