Comparison study on the antibacterial activity of nano- or bulk-cerium oxide

Due to the unique physical and chemical properties, nanosized cerium oxide (n-CeO2) has attracted considerable interest in many fields of research. The potential, the growing use and the mass production of n-CeO2 have stimulated research on their potential impact on the environment and human health. However, the toxicological definition for CeO2 nanoparticles (NPs) is still quite controversial. In the present work, we evaluated the antibacterial activity of CeO2 NPs sized ca. 7 nm (7-CeO2), ca. 25 nm (25-CeO2) and their bulk counterpart (b-CeO2), using gram-negative Escherichia coli (E. coli). Our results suggest that all the three types of CeO2 particles have antibacterial activity, and both the NPs are more toxic than b-CeO2. The rise in intracellular ROS level induced by direct contact of particles with the surface of E. coli was involved in the mechanism for the antibacterial activity of CeO2 NPs. Exposure to 25-CeO2 could also impair the integrity of the outer membrane within E. coli cells. Due to agglomeration and negligible effect on membrane integrity, 7-CeO2 did not exhibit greater antibacterial activity than 25-CeO2.