Purpose: To assess the attachment abilities of Salmonella to vegetables seeds with different surface characteristics.
Methods: Chemically treated vs. untreated and intact vs. mechanically damaged seeds of alfalfa, fenugreek, tomato and lettuce were artificially contaminated with nalidixic acid resistant cells of 4 Salmonella strains at 20oC for 5 h. Contaminated seeds were rinsed twice with 10 ml of sterile water and then soaked overnight in 5 ml of phosphate buffered saline (pH 7.40) at 4oC. Seeds were then vortexed vigorously, and seed soaking solutions were plated onto bismuth sulfite agar, tryptic soy agar (TSA) and TSA supplemented with nalidixic acid. The ratio of the number of attached cells to the number of inoculated cells was reported as attachment rate. Student t-tests were performed to determine the significance of differences among each pathogen attached to each type of seeds.
Results: The attachment rate of Salmonella on different types of seeds varied from 0.1% - 38.2%. Overall, the attachment rate of Salmonella was the highest (18.7%) on lettuce seed, followed by tomato seed (13.2%), alfalfa seed (11.3%) and fenugreek seed (6.0%). Salmonella attachment to mechanically damaged seeds (17.4%) was significantly higher (P < 0.05) than to intact seeds (7.2%). Pathogen attachment to untreated seeds (13.4%) was significantly (P < 0.05) higher than to chemically treated seeds (11.2%). Each Salmonella strain had a unique attachment pattern although the overall attachment abilities of the 4 strains were not significantly different.
Significance: Data suggest that Salmonella can attach to vegetable seeds and pathogen attachment rate varies with seed type and surface characteristics. Mechanically damaged and non-chemically-treated seeds are more vulnerable to Salmonella contamination.