The task of this final work from the Food Microbiology course was to find the bacterium of Pseudomonas aeruginosa in wastewater. The practical part of the bacterial finding and disinfection of water was carried out at a licensed laboratory of Vodovod d.o.o. Slavonski brod at the watercourse Jelas. The experiment was conducted on water samples taken to find the bacterium Pseudomonas aeruginosa. In the theoretical part of the final work, we described the history and classification of Pseudomonas genus, as well as the Pseudomonas aeruginosa bacteria. Briefly, we have outlined the features of the bacterium, such as morphology, biochemical properties, resistance, toxicity, epidemiology, pathogenesis for humans and animals, colonization and diagnosis. When the task of finding a bacterium by membrane filtration in a sample of wastewater was done, the next task was to find a chlorine concentration that would completely destroy the bacterium Pseudomonas aeruginosa. That is to make the disinfection of water in which we found that bacterium. Once the sample of bacterial water is found, disinfection with chlorine was made depending on the time. Chlorine disinfection was interrupted with Na2S2O3 sodium thiosulfate in the time intervals which are previously set. 100 ml water samples were filtered through vacuum with procedure of membrane filtration through a 0,45 μm membrane filter paper. Everything was done under sterile conditions as described in detail in the work. After incubation for 48 h at 37 °C, the results given where given on the paper.