Persistence of Probiotic Lactic Acid Bacteria in Nutrient Film Technique Hydroponic Systems and In Vitro Against Salmonella spp

Lactic acid bacteria (LAB) are gram-positive, non-spore-forming microorganisms acknowledged for their probiotic and antimicrobial properties against foodborne pathogens, including Salmonella spp. This study investigated the viability of three pre-harvest LAB treatments: Enterococcus faecium L-20B, Lactiguard™, and Probicon in cilantro (Coriandrum sativum) grown in a hydroponic system and the effectiveness of these three LAB treatments against Salmonella spp. in vitro. In the in vitro assay, various LAB concentrations (6, 7, 8, and 9 Log CFU/mL) were co-inoculated with a Salmonella cocktail (initial inoculation level of 4 Log CFU/mL, containing S. Enteritidis and S. Typhimurium) and incubated at 10°C for 72 hours. The results indicated that greater concentrations (8 and 9 Log CFU/mL), particularly Lactiguard™, reduced Salmonella to below the detection limit (< 1.4 Log CFU/mL) after 72 h, whereas lower concentrations exhibited limited effectiveness. To determine the application potential of these LAB treatments in a nutrient film technique hydroponic system, the viability of the LAB treatments (9 Log CFU/mL) was assessed over a 16-day growth cycle in cilantro plants. All strains demonstrated survival throughout the study; however, a notable 3-5 Log CFU/mL decline was observed beginning on day 2 (P < 0.05). By day 5, significant sediment formation was detected, which impeded nutrient recirculation and raised concerns about LAB use in Nutrient Film technique (NFT) systems. These findings demonstrated that LAB can effectively reduce Salmonella under in vitro conditions and remain viable in hydroponic environments. However, a filtering technology would need to be implemented to mitigate sediment formation within the NFT system.