Exposure to TiO$_{\mathrm{2}}$ nanoparticles increases Staphylococcus\textit{ aureus }infection of HeLa cells

TiO$_{\mathrm{2}}$ is one of the most common nanoparticles in industry from food additives to energy generation. Even though TiO$_{\mathrm{2}}$ is also used as an anti-bacterial agent in combination with UV, we found that, in the absence of UV, exposure of HeLa cells to TiO$_{\mathrm{2}}$ nanoparticles largely increased their risk of bacterial invasion. HeLa cells cultured with low dosage rutile and anatase TiO$_{\mathrm{2}}$ nanoparticles (0.1 mg/ml) for 24 hrs prior to exposure to bacteria had 350{\%} and 250{\%} respectively more bacteria infected per cell. The increase was attributed to increased LDH leakage, and changes in the mechanical response of the cell membrane. On the other hand, macrophages exposed to TiO$_{\mathrm{2}}$ particles ingested 40{\%} fewer bacteria, further increasing the risk of infection. In combination, these two factors raise serious concerns regarding the impact of exposure to TiO$_{\mathrm{2}}$ nanoparticles on the ability of organisms to resist bacterial infection.