Purpose: Characterize Salmonella serotypes isolated from three biodiverse tomato farms to determine environmental reservoirs, potentially leading to remediation strategies.
Methods: Environmental samples were collected (2012 – 2014) during tomato production seasons from 3 N.C. farms. Field (tomato fruit, blossom, leaf, weeds, soil) and water samples (n = 1547) were analyzed for Salmonella by enrichment using a modified BAM method as well as by real-time PCR. Isolates were serotyped and genotyped by pulse-field gel electrophoresis. In addition, generic E. coli was enumerated in water samples using the IDEXX Colilert and quanti-tray 2000 system.
Results: Salmonella was isolated (n = 169) in June (23 isolates), July (46 isolates), August (55 isolates), and September (45 isolates). Environmental sources for these isolates were water (58%; 98/169), sediment (30%; 50/169), tomato fruit (10%; 17/169), and soil (2%; 4/169). Of the serotypes identified through PulseNet with potential clinical significance (87/169), 22% (37/169) were Paratyphi B (monophasic from water and sediment); 11% (19/169) were Newport (water and sediment); 7% (12/169) were Typhimurium (water and sediment); 5% (8/169) were Hartford (sediment); 3% (two sets of 5/169) were Agona and Montevideo (sediment and tomato, respectively); and 0.6% (1/169) were Berta (sediment).
Significance: This project establishes three years of correlation between N.C. tomato production environments and the occurrence of clinically significant Salmonella serotypes. Recurring agricultural niches for this human pathogen were source water and sediments in each of the production seasons. Determining relationships between raw agricultural commodities, pathogen serotypes, and environmental reservoirs can assist in developing strategies to reduce commodity-pathogen risks for our farming communities.