ZnO and TiO2 nanoparticles as novel antimicrobial agents for oral hygiene: a review

Direct observations have clearly shown that biofilm bacteria predominate, numerically and metabolically, in virtually all nutrient-sufficient ecosystems. Therefore, these sessile organisms predominate in most of the environmental, industrial, and medical problems and processes of interest to microbiologists. If biofilm bacteria were simply planktonic cells that had adhered to a surface, this revelation would be unimportant, but they are demonstrably and profoundly different. We first noted that biofilm cells are at least 500 times more resistant to antibacterial agents. Now we have discovered that adhesion triggers the expression of a sigma factor that derepresses a large number of genes so that biofilm cells are clearly phenotypically distinct from their planktonic counterparts. Each biofilm bacterium lives in a customized microniche in a complex microbial community that has primitive homeostasis, a primitive circulatory system, and metabolic cooperativity, and each of these sessile cells reacts to its special environment so that it differs fundamentally from a planktonic cell of the same species.

In this work we investigated the antibacterial properties of differently shaped silver nanoparticles against the gram-negative bacterium Escherichia coli, both in liquid systems and on agar plates. Energy-filtering transmission electron microscopy images revealed considerable changes in the cell membranes upon treatment, resulting in cell death. Truncated triangular silver nanoplates with a {111} lattice plane as the basal plane displayed the strongest biocidal action, compared with spherical and rod-shaped nanoparticles and with Ag(+) (in the form of AgNO(3)). It is proposed that nanoscale size and the presence of a {111} plane combine to promote this biocidal property. To our knowledge, this is the first comparative study on the bactericidal properties of silver nanoparticles of different shapes, and our results demonstrate that silver nanoparticles undergo a shape-dependent interaction with the gram-negative organism E. coli.

Periodontitis, or gum disease, affects millions of people each year. Although it is associated with a defined microbial composition found on the surface of the tooth and tooth root, the contribution of bacteria to disease progression is poorly understood. Commensal bacteria probably induce a protective response that prevents the host from developing disease. However, several bacterial species found in plaque (the 'red-complex' bacteria: Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola) use various mechanisms to interfere with host defence mechanisms. Furthermore, disease may result from 'community-based' attack on the host. Here, I describe the interaction of the host immune system with the oral bacteria in healthy states and in diseased states.