Purpose: This study was undertaken to determine whether Salmonella on artificially inoculated and accompanying contaminated vegetable seeds could migrate to different tissues of sprouts/seedlings.
Methods: Alfalfa, fenugreek, tomato and lettuce seeds were inoculated with different nalidixic acid-resistant strains of Salmonella (B, C, M, S) by artificial inoculation (IN) or accompanying contamination (AC). For IN, overnight Salmonella culture was co-incubated with the vegetable seeds at 20°C for 5 h, whereas for AC, freeze-dried Salmonella cells in sterile sandy soil were co-incubated with the vegetable seeds at 20°C for one day. Contaminated vegetable seeds were subsequently germinated on 1% water agar at 25°C in the dark. Populations of Salmonella on different tissues (seed coat, cotyledon, stem and radicle) of the sprouts/seedlings were determined every other day for 5 days. Data was analyzed by Fisher’s LSD using SAS software.
Results: Approximately 94% and 64% of the samples inoculated by IN and AC, respectively, tested positive for Salmonella. For both inoculation methods, seed coats had the highest Salmonella level (5.35 log for IN and 3.59 log for AC), followed by radicle (5.12 log for IN and 3.40 log for AC), cotyledon (5.00 log for IN and 3.25 for AC) and stem (4.50 log for IN and 2.92 for AC). Artificially inoculated fenugreek seeds had the highest Salmonella level (5.81 log), followed by alfalfa (5.67 log), lettuce (5.48 log) and tomato (1.54 log) seeds. For AC, lettuce seeds had a higher Salmonella level (3.80 log) than alfalfa seeds (2.26 log). For both inoculation methods, strain M had the lowest rate of recovery.
Significance: These data suggest that Salmonella migrated from artificially inoculated and accompanying contaminated vegetable seeds to various tissues of sprouts/seedlings during germination, indicating the importance of using pathogen-free seeds for vegetable sprout/seedling production.