To investigate the pH tolerance of the bacterium Escherichia Coli

The aim of this experiment was to find out the pH tolerance of E.Coli. Hence, in this extended essay there is a comparison of the optical density of E.Coli in different pH levels. These pH levels are chosen to investigate the E.Coli activity in acidic medium. My research question was “How do different pH levels affect the growth of Escherichia Coli by measuring its optical density via spectrophotometer?” According to the research question my hypothesis was “As the pH level of the medium increases, it will be more likely for E.Coli to die.” In this experiment spectrophotometric method was used to measure the optical density of E.Coli in 3, 4, 5, 6, 7 and 8 pH levels. These pH levels are chosen so that experiment includes both acidic and neutral medium and the comparison of E.Coli activity can be made easily. Liquid broths with different pH levels were prepared and were put in bacteriological incubator for 1 day at a stable temperature. After 1 day the optic densities of these liquid broths were measured via spectrophotometer. Optical densities of these liquid broths illustrated the reproduction of the E.Coli. Higher optical density illustrates more reproduction of the bacteria. The optical density is higher in 6, 7 and 8 pH levels and this means that there is more reproduction of E.Coli in those pH levels. On the other hand the optical density of 3, 4 and 5 pH levels were low comparing other pH levels. As a result of this experiment it can be said that E.Coli can live in neutral and die in acidic medium