Surveillance of Salmonella Typhimurium in Hydroponic Basil (Ocimum basilicum) Systems under Varying Nutrient Solution Electrical Conductivities

Abstract

This study aimed to evaluate the influence of electrical conductivity (EC) levels of the nutrient solution on the survival of Salmonella Typhimurium in hydroponic basil (Ocimum basilicum) grown under the Nutrient Film Technique (NFT). Pathogen survival was analyzed in nutrient solution, roots, surfaces, and leaves under four EC levels (1.0, 1.3, 1.6, and 2.0 mS·cm⁻¹) during a 28-day crop cycle. The system was inoculated with S. Typhimurium at ~8 log CFU/mL (2 mL added to 7.6 L per reservoir), and samples were collected at multiple time points. Data were analyzed using non-parametric tests (Shapiro–Wilk and Kruskal–Wallis, p < 0.05). Results showed that EC had no significant effect (p > 0.05), while time was highly significant (p < 0.001). A biphasic decline was observed: rapid from days 1–7 and slower until day 28. Nutrient solution showed the highest initial counts, roots and surfaces tested positive in early stages, and leaves remained consistently negative. No significant interaction between EC and time was detected. Overall, S. Typhimurium persisted at low levels in nutrient solution, roots, and surfaces until day 28, while leaves stayed free of contamination. These findings demonstrate that survival trends were driven by time rather than EC, and that persistence in hydroponic NFT systems represents a potential risk for cross-contamination.