Titanium dioxide nanoparticles (nano-titania/TiO2 NPs) are used in different fields and applications. However, the release of TiO2 NPs into the environment has raised concerns about their biosafety and biosecurity. In light of the evidence that TiO2 NPs could be used to counteract antibiotic resistance, they have been investigated for their antibacterial activity. Studies reported so far indicate a good performance of TiO2 NPs against bacteria, alone or in combination with antibiotics. However, bacteria are able to invoke multiple response mechanisms in an attempt to adapt to TiO2 NPs. Bacterial adaption arises from global changes in metabolic pathways via the modulation of regulatory networks and can be related to single-cell or multicellular communities. This review describes how the impact of TiO2 NPs on bacteria leads to several changes in microorganisms, mainly during long-term exposure, that can evolve towards adaptation and/or increased virulence. Strategies employed by bacteria to cope with TiO2 NPs suggest that their use as an antibacterial agent has still to be extensively investigated from the point of view of the risk of adaptation, to prevent the development of resistance. At the same time, possible effects on increased virulence following bacterial target modifications by TiO2 NPs on cells or tissues have to be considered.
Keywords: TiO2 NPs; bacterial adaptation; nano-titania; nanoparticle resistance; risk assessment; toxicity.