Critical assessment of suitable methods used for determination of antibacterial properties at photocatalytic surfaces.

This work describes the development of methods necessary for antibacterial effect evaluation on irradiated TiO(2) layers. Two methods using bacteria suspensions and the glass adhesion method (based on ISO 27447:2009(E)) were critically assessed and compared. As test bacteria gram negative Escherichia coli and gram positive Enterococcus faecalis were employed. The method using 50 cm(3) of bacteria suspension is convenient for testing layers with strong antibacterial effect (prepared from powder photocatalysts). For the evaluation of the antibacterial effect of sol gel layers, the glass adhesion method based on the ISO is more appropriate than the method with 3 cm(3) of bacteria suspension. The reason is that the later does not allow a distinction between the inhibition effect of TiO(2) and UV light itself. Some improvements of the ISO method were suggested, namely the use of gelatinous pills (CCM) of bacteria, using saline solution instead of nutrient broth for bacteria suspension preparation and the application of selective media for bacteria cultivation. Decreasing the light intensity from 0.6 mW cm(-2) to 0.2 mW cm(-2) (fulfilling the requirements of the ISO) results in almost negligible effect of UV light itself, thus enabling proper testing of the antibacterial properties of TiO(2) thin films.