Water contamination by various bacteria, viruses and other pathogens is a great threat to human health. Amongst other Advanced Oxidation Processes TiO2 photocatalysis is considered as one of the most efficient treatment for the polluted wastewater disinfection. Usually, the wastewater produced by higher risk objects, such as hospitals, implicates diverse contaminants, but efficiency of most of the Advanced Oxidation Processes is tested by using only single pathogens and information on inactivation of bacteria mixtures is still limited. In this study, photocatalytical inactivation of three commonly found bacterial pathogens (gram-positive (Micrococcus luteus) and gram-negative (Salmonella enterica, Escherichia coli)) was investigated. Efficiency of traditional photocatalytic disinfection process using single bacterial pathogens was compared to the one observed for their mixtures. The impact of photocatalytical process parameters and treatment time on bacteria disinfection efficiency was studied. Photocatalytic disinfection efficiency testing with bacteria mixtures revealed, that in the presence of TiO2 photocatalyst and UV irradiation tested gram-positive cells were inactivated slower than gram-negative cells. Another important finding was that an overall photocatalytic disinfection efficiency of bacteria mixtures is not a straight forward sum of inactivation rates of individually tested pathogens but has a strong relationship to the properties of their competitive growth.