THE VIABILITY OF E. COLI IN SEA WATER AT DIFFERENT TEMPERATURES

The accidental multiplication of conditional pathogen bacteria such as E. coli in the territorial sea waters of Romania has an important impact on human health and requires a continuous evaluation of its risks. This study is focused on the effect of some physical factors (temperature, salinity, nutrient concentration) on the viability of Escherichia coli cells. In our experiments, we analysed the response of E. coli grown in normal conditions (LB at 37 degrees C) when subjected to a nutritional, saline and osmotic shock by introducing sub-samples of the culture in three (4 degrees C, 15 degrees C, 37 degrees C) separate sterile sea water (sea water filtered through a Millipore filter-pores of 0.22 mu m) microcosms. The samples were collected at different times (ranging from minutes to days) and analysed with respect to total cell densities (cells permeable to Syber green), dead cells (cells permeable to propidium iodide) densities and colony forming units. The results showed that the stress conditions determined by osmotic shock, saline shock and nutrients deprivation cannot suppress the resistance and multiplication capacity of E. coli after two days, even though the stress conditions diminished them. Although the temperature of the sea water is an important factor regarding the resistance of E. coli, a rather large proportion of cells continue to remain alive at 4 degrees C, and able to multiply when transferred to LB at 37 degrees C.