Purpose: To compare the attachment abilities of different STEC strains to vegetable seeds with different surface integrity properties and chemical treatment practices.
Methods: Two different levels of nalidixic acid (NA) resistant cells of O157:H7 (F, K and H) and O104:H4 (G) strains were co-incubated with mechanically damaged and intact, as well as chemically treated and untreated, alfalfa, fenugreek, tomato and lettuce seeds at room temperature for 5 h. Contaminated seeds were rinsed with sterile water then soaked overnight in phosphate buffered saline at 4oC. Seed soaking solutions were plated onto tryptic soy agar (TSA) as well as TSA and sorbitol MacConkey agar supplemented with NA. Pathogen attachment rate was expressed as the ratio of the number of attached cells to number of inoculated cells. Fisher’s least significant difference test was used to determine the significance of difference among the tested pathogens on different vegetable seeds.
Results: Overall, the number of attached STEC cells was the highest (10.4%) on lettuce seed, followed by tomato (4.8%), alfalfa (2.5%) and fenugreek (1.8%) seeds. The ability of STEC cells to attach to the damaged seeds (6.4%) was significantly higher (P < 0.05) than to intact seeds (3.3%) whereas no significant difference was observed between pathogen attachment to chemically treated vs. untreated seeds. Strain K displayed the best attachment ability on the tested seeds (12.5%), followed by F (5.2%), H (1.5%) and G (0.2%).
Significance: This work highlights the difference in attachment ability of STEC strains on various vegetable seeds. The rate of STEC attachment was influenced by seed surface integrity and chemical treatment practice.