Fate of various Salmonella enterica and enterohemorrhagic Escherichia coli cells attached to alfalfa, fenugreek, lettuce, and tomato seeds during germination

Contaminated vegetable seeds have been identified as a potential source of foodborne pathogens. This study was undertaken to observe the physiological behavior of various Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) cells attached to different types of vegetable seeds during germination. Surface-sanitized seeds (2 g) of alfalfa, fenugreek, lettuce, and tomato were exposed to four individual strains of Salmonella (Baildon, Cubana, Montevideo, and Stanley) or EHEC (three O157:H7 and one O104:H4 strain[s]) at 20 °C for 1 h. Vegetable seeds with attached bacterial cells were germinated on 1% water agar at 25 °C in the dark. Populations of Salmonella and EHEC on various tissues of sprouts/seedlings (seed coat, root, cotyledon, stem, etc.) were determined every other day over a 9-day germination period. The mean populations of Salmonella and EHEC on sprout/seedling tissues increased as the prolongation of germination time. Overall, 93.0% and 92.3% of collected tissue samples (n = 544) tested positive for Salmonella and EHEC, respectively. Seed coats had significantly higher (P < 0.05) bacterial counts (7.8 log CFU/g) compared to the root, cotyledon, and stem tissues (7.1–6.2 log CFU/g). On average, lettuce seedlings and alfalfa sprouts had significantly higher (P < 0.05) numbers of Salmonella and EHEC cells, followed by fenugreek sprouts, and tomato seedlings. The E. coli O104:H4 strain established the lowest (P < 0.05) cell population (5.2 log CFU/g) on sprout/seedling tissues among all EHEC strains used in the study. Among the three E. coli O157:H7 strains, F4546 (7.2 log CFU/g) and H1730 (7.0 log CFU/g) had significantly (P < 0.05) higher mean cell population than K4499 (6.8 log CFU/g). The mean population of S. Cubana (7.0 log CFU/g) was significantly higher (P < 0.05) than the populations of the other 3 Salmonella strains (6.5–6.6 log CFU/ g) used in this study. These data suggested that the growth and dissemination of Salmonella and EHEC cells on alfalfa, fenugreek, lettuce, and tomato sprouts/seedlings were influenced by the bacterial strains, type of sprouts/seedlings, and specific sprout/seedling tissues involved.