Effects of culture conditions and tomato, spinach and lettuce lysates on adherence to intestinal epithelial cells of Salmonella Typhimurium PT 193

The present study examined the effects of tomato, spinach and lettuce lysates on the adherence of Salmonella Typhimurium PT193 (S. Typhimurium) to Caco-2 cells. Different culture conditions and growth media were examined first. S. Typhimurium grown in Luria-Bertani (LB) broth adhered poorly to Caco-2 cells compared to growth in tryptic soy broth (TSB) and in brain heart infusion (BHI) broth. Culturing with or without agitation did not affect the bacterial adherence. Addition of NaHCO3 to the media reduced Salmonella adherence by 50% compared with that without NaHCO3. When tomato, baby spinach, and Romaine lettuce lysates were incubated with S. Typhimurium for 1 h, 5 h, and 24 h at 28 °C, survival of Salmonella in the lettuce lysate was reduced by 0.5–0.6 log after 5 h and 24 h incubation compared to the control. The lysate from spinach enhanced the adherence of S. Typhimurium to Caco-2 cells by 2.0 and 3.1 fold during early incubation at 1 h and 5 h; similarly, the tomato lysate increased the adherence by 2.7 and 2.3 fold at 5 h and 24 h, respectively, compared to the control. The effects of tomato lysate on the survival and adherence of Salmonella did not appear related to its acidic pH (4.8), although more acidic pH (3.5) reduced Salmonella survival and adherence by 1.0 log and 90%, respectively, at 24 h incubation compared to the control at pH 7.4. These data suggest that plant factors may promote the virulence of S. Typhimurium for human infection by increasing adherence.