Purpose: In this study, tomato plants were inoculated with S. enterica serotypes to evaluate plausible internalization routes and to determine if there is any niche fitness for certain serovars.
Methods: A cocktail of five S. enterica serotypes was used to inoculate tomato plants (cultivar: Micro-Tom) by spotting leaflets or brushing blossoms with inoculum, or by inoculating soil right after transplanting. Molecular serotyping was used to survey serotypes of 100 colonies, each randomly picked from Salmonella positive soil-root, leaflet, and blossom samples. Stem walking was used to trace the internal movement of Salmonella from the root. Both surface and interior of green or ripe tomato fruits were examined for Salmonella as well.
Results: Soil inoculation led to Salmonella internalization in 3 of 40 plants, and contamination of one of 30 tomatoes assayed. Of 71 tomatoes harvested from inoculated blossoms, 49 (69%) surface samples were positive for Salmonella, and 22 (31%) interior samples were positive from the 49 Salmonella positive tomatoes. Of the five serotypes inoculated, Newport and Javiana were the most dominant in soil at both days 8 and 23. On tomato leaflets, although all five serotypes, except Typhimurium, were evenly distributed at day 8, only Newport and Montevideo remained dominant at day 23. Montevideo was the most prevalent serotype on blossoms at day 7.
Significance: Results suggest that soil and tomato blossoms are possible sites for Salmonella internalization, and for the first time, Salmonella serotype-specific niche adaptation on the tomato plant was demonstrated.