Figure 1.
Effect of iron on growth of enteric bacteria.
Effect of various concentrations of ferric citrate on in vitro growth of (A) S. typhimurium, (B) C. freundii, (C) E. coli, (D) E. faecalis and (E) L. plantarum.
Figure 2.
Effect of iron on bacterial adhesion to an epithelial monolayer.
Adhesion (mean+SD) of enteric bacteria to a monolayer of Caco-2 cells is given as percentage of the inoculum. A: S. typhimurium, n = 8. B: C. freundii, n = 4. C: E. coli, n = 6. D: E. faecalis, n = 6. E: L. plantarum, n = 5. Means without a common letter differ, P<0.05. Notably, adhesion data of S. typhimurium were derived from 4 separate experiments performed at 13, 15, 18 and 21 days post-seeding of Caco-2 cells. The fact that each experiment revealed the same trend is indicative for similar physiochemical properties of the monolayer at these time points.
Figure 3.
Effect of iron on invasion of S. typhimurium into epithelial cells.
Invasion (mean+SD) of S. typhimurium into Caco-2 cells, n = 2. Invasion after 3.5 h is given as percentage of the inoculum. The inoculum was removed after 2 hours of adhesion time. Means of 0–10 µmol/L ferric citrate were compared by one-way ANOVA.
Figure 4.
Effect of iron on the ability of S. typhimurium to cross and deteriorate an epithelial monolayer.
Effect of iron on the ability of S. typhimurium to cross an epithelial monolayer of Caco-2 cells and the integrity of this monolayer. A: The translocation is given as percentage of the inoculum (mean+SD), n = 2. Means without a common letter differ, P<0.07. B: The integrity of the Caco-2 monolayer during S. typhimurium (St) and L. plantarum (Lp) translocation, monitored by TEER measurements.
Figure 5.
Effect of iron on the ability of enteric bacteria to induce cell damage.
LDH-release (mean+SD) as a measure of cell damage of Caco-2 cells upon co-incubation with S. typhimurium (St, n = 5), C. freundii (Cf, n = 4), E. coli (Ec, n = 4), E. faecalis (Ef, n = 4), and L. plantarum (Lp, n = 2) pre-incubated with or without ferric citrate. The percentage LDH release compared to the control (no bacteria) was corrected for the number of bacteria in the medium (average between t = 0 and t = 2 h). Means within a group and without a common letter differ significantly, P<0.05.