Figure 1.
Transmission electron microscopy of TiO2 nanoparticles and size distribution performed by scanning electron microscopy.
Single particle characterization was performed by filtering stock TiO2 NPs suspension on polycarbonate membranes. For TEM, samples were coated with a carbon film and then the polycarbonate was dissolved by chloroform. For SEM, filters, mounted on stubs, were coated with a thin gold film.
Figure 2.
Effect of TiO2 NPs on growth of LM2 and LM9 strains.
Bacterial cells were inoculated in TSB+YE supplemented with TiO2 NPs at concentrations of 0, 0.08, 0.8, 8, 80 µg/ml. Values are expressed as mean ± SD. All experiments were carried out in triplicate and repeated in two independent sets of experiments.
Figure 3.
Effect of TiO2 NPs on biofilm formation by Listeria monocytogenes strains.
Wells of polystyrene microtiter plates were conditioned with TSB-YE medium or with TiO2 NPs at 0.08, 0.8, 8, and 80 µg/ml. Biofilm cells were indirectly quantified by crystal violet staining and absorbance measurements at 590 nm. Values are expressed as mean ± SD. All experiments were carried out in sextuple and repeated in two independent set of experiments. Asterisks denote statistically significant increase of the Listeria population compared to control bacterial cells (*p<0.05; **p<0.01; ***p<0.001).
Figure 4.
Scanning electron microscopy observations of LM2 strain biofilm formation.
Bacteria were allowed develop biofilm on glass slide for 482 NPs at different concentrations. Micrograph shows representative images of untreated (A–C) or 80 µg/ml TiO2 NPs (B–D) treated bacterial cells.
Figure 5.
Scanning electron microscopy observations of LM9 strain biofilm formation.
Bacteria were allowed develop biofilm on glass slide for 482 NPs at different concentrations. Micrograph show representative images of untreated (A–C) or 80 µg/ml TiO2 NPs (B–D) treated bacterial cells.
Figure 6.
Scanning electron microscopy and energy-dispersive X-ray spectroscopic (EDX) analysis of LM2 and LM9 strains.
LM2 untreated bacteria (A–B); LM2 strain exposed to 80 µg/ml TiO2 NPs (C–D); LM9 strain exposed to 80 µg/ml TiO2 NP (E–F). EDX spectra represent the qualitative elemental analysis of the extracellular matrix surrounding bacterial cells.
Figure 7.
CaCo-2 adhesion and invasion efficiency of LM2 and LM9 strains in absence or in presence of TiO2 NPs at different concentrations.
Values were expressed as percentage of control untreated bacteria. Both adhesion and invasion were performed in triplicate and three independent experiments were carried out for each strain. Asterisks denote statistically significant values compared to control bacterial cells (*p<0.05; **p<0.01; ***p<0.001).
Table 1.
Replication index (RI) of listeria strains in CaCo-2 cells in presence of TiO2 NPs.