AUTHOR=Radziwill-Bienkowska Joanna M. , Talbot Pauline , Kamphuis Jasper B. J. , Robert Véronique , Cartier Christel , Fourquaux Isabelle , Lentzen Esther , Audinot Jean-Nicolas , Jamme Frédéric , Réfrégiers Matthieu , Bardowski Jacek K. , Langella Philippe , Kowalczyk Magdalena , Houdeau Eric , Thomas Muriel , Mercier-Bonin Muriel 

TITLE=Toxicity of Food-Grade TiO2 to Commensal Intestinal and Transient Food-Borne Bacteria: New Insights Using Nano-SIMS and Synchrotron UV Fluorescence Imaging

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00794

DOI=10.3389/fmicb.2018.00794

ISSN=1664-302X

ABSTRACT=<p>Titanium dioxide (TiO<sub>2</sub>) is commonly used as a food additive (E171 in the EU) for its whitening and opacifying properties. However, a risk of intestinal barrier disruption, including dysbiosis of the gut microbiota, is increasingly suspected because of the presence of a nano-sized fraction in this additive. We hypothesized that food-grade E171 and Aeroxyde P25 (identical to the NM-105 OECD reference nanomaterial in the European Union Joint Research Centre) interact with both commensal intestinal bacteria and transient food-borne bacteria under non-UV-irradiated conditions. Based on differences in their physicochemical properties, we expect a difference in their respective effects. To test these hypotheses, we chose a panel of eight Gram-positive/Gram-negative bacterial strains, isolated from different biotopes and belonging to the species <italic>Escherichia coli</italic>, <italic>Lactobacillus rhamnosus</italic>, <italic>Lactococcus lactis</italic> (subsp. <italic>lactis</italic> and <italic>cremoris</italic>), <italic>Streptococcus thermophilus</italic>, and <italic>Lactobacillus sakei</italic>. Bacterial cells were exposed to food-grade E171 vs. P25 <italic>in vitro</italic> and the interactions were explored with innovative (nano)imaging methods. The ability of bacteria to trap TiO<sub>2</sub> was demonstrated using synchrotron UV fluorescence imaging with single cell resolution. Subsequent alterations in the growth profiles were shown, notably for the transient food-borne <italic>L. lactis</italic> and the commensal intestinal <italic>E. coli</italic> in contact with food-grade TiO<sub>2</sub>. However, for both species, the reduction in cell cultivability remained moderate, and the morphological and ultrastructural damages, observed with electron microscopy, were restricted to a small number of cells. <italic>E. coli</italic> exposed to food-grade TiO<sub>2</sub> showed some internalization of TiO<sub>2</sub> (7% of cells), observed with high-resolution nano-secondary ion mass spectrometry (Nano-SIMS) chemical imaging. Taken together, these data show that E171 may be trapped by commensal and transient food-borne bacteria within the gut. In return, it may induce some physiological alterations in the most sensitive species, with a putative impact on gut microbiota composition and functioning, especially after chronic exposure.</p>