Letospira interrogans serovar Canicola Antibacterial effects of TiO 2 nanoparticles combine with UVA on Letospira interrogans serovar Canicola 1 , 1,2 , 3 , 1 Sudarat Chadsuthi 1 , Wannapong Triampo 1,2 , Galayanee Doungchawee 3 , Jirasak Wong-ekkabut 1 1 Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand 2 Capability Building Unit in Nanoscience and Nanotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand 3 Department of Pathobiology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand : (TiO 2 -NP) (UVA) Canicola 10 8 cells/ml TiO 2 -NP 50 g/ml UVA 2, 6 24 24 TiO 2 -NP immunoblotting 21 48 kDa TiO 2 -NP UVA TiO 2 -NP Abstract: TiO 2 nanoparticles (TiO 2 -NP) combine with Ultraviolet-A (UVA) radiation were recently reported as the photocatalytic disinfection process. Our study is to investigate the antimicrobial effects of TiO 2 -NP on L. interrogans serovar Canicola represented as pathogenic leptospires that cause leptospirosis. The bacteria were cultured and treated by TiO 2 -NP, UVA radiation at variable time duration of 2, 6 and 24 hr with and without TiO 2 -NP at 50 g/~10 8 cells-ml. The results show that samples with higher dose UVA (112.3 W-sec/cm 2 ) both with and without TiO 2 -NP have higher antimicrobial effects resulting in the decrease in the growth and viability of bacteria when compared with those without UVA exposure. By immunoblotting method, Leptospiral antigen components about 21 and 48 kDa disappear when compared with non-exposed control. Only TiO 2 treatment alone does not significantly give any difference from the control (no treatment) samples. From our preliminary works, it may be concluded that the UVA play a major role on antimicrobial effects while the TiO 2 -NP affect bacteria only when photocatalysis is occurred. Further studies with TiO 2 -NP must be carried out using such as different doses and/or exposure periods if we want to reach a better understanding.