Introduction: Phosphorus is an essential chemical element for all living organisms because it is the key molecule for the functioning and life of all living things. Phosphorus is often a neglected element as a limiting nutrient for bacterial growth and reproduction. In drinking water, one of the sources of phosphorus might be an addition of plasticizers to prevent boiler formation of lime stone. This can be a nutrient to the bacteria which are present in drinking water, leading to an increase in the number of not only harmless bacteria but also an increase in the number of pathogenic bacteria, including Escherichia coli strains. It is one of the most commonly reported bacteria in drinking water since its presence indicates fecal contamination of water. Purpose: The aim of the master's thesis is to investigate the positive relationship between addition of different types of phosphate preparations at different concentrations and their effect on the reproduction of the E. coli test bacterium. Methods: E. coli bacterial culture were exposed to various concentrations of phosphorus and their reaction of was followed at 0, 24, 48 and 72 hours. Growth of bacterial culture was done on ordinary agar after 48 hours at temperature of 36 °C. All analyzes were performed in parallel duplicates and repeated three times. Results: The results of our research indicate a probable correlation between the addition of different concentrations of different phosphate preparations and regrowth of bacteria E. coli, but this correlation was not statistically proven in our study. Bacteria responded the best to the higher concentrations of sodium phosphate(V). With the addition of a commercial water softener bacteria also multiplied better in the presence of it. Discussion and conclusion: Based on the obtained results, we can conclude that the addition of phosphorus probably have significant affect on the reproduction of bacteria E. coli. It should be emphasized that the experiment was conducted in controlled laboratory circumstances, which excluded factors from the real environment (pH, temperature, presence of other bacterial species, surface materials, flow rate, etc.) that could have possibly affected reproduction of bacteria. For further undernstanding the influence of phosphates on the reproducition of E. coli the research can be repeated on a larger scale of samples and not only in laboratory conditions but also in simulated enviroment of water supply system.
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