Escherichia coli survival in the water from the Gulf of Gdansk under laboratory conditions
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Faecal coliform bacteria (among others Escherichia coli) are routinely used in monitoring of water areas (first of all seaside resorts). Their occurrence indicates recent pollution by municipal sewage. Survival of these bacteria in the sea water depends on the complex of biological, chemi-cal and physical water parameters. There are many conflicting opinions on bacterial death-rate and the data on this phenomenon for the Gulf of Gdansk are rather scarce. The influence of irradi-ance (0-200 mumol photon m-2 s-1), temperature (5-20 ?C) and salinity (0-7.5 psu) on the survival of Escherichia coli strain K-12 has been investigated. The bacterial cultures were incubated for three days under chosen temperature, salinity and irradiance conditions. Experiments were planned based on the factorial design (method x'). The cell density was determined every day by direct viable count on agar plates. The obtained results were analysed statistically in such a way that temperature, salinity and irradiance were independent variables whereas Escherichia coli number and mean mortality coefficient (Km) were the dependent ones. It was found that the effect of salinity (in studied range from 0 to 7.5 psu) on Escherichia coli survival was not statistically significant. However, the survival was strongly correlated with temperature and irradiance. Correlation coefficient (R) between temperature and irradiance and mean coefficient of Escherichia coli mortality (Km) equalled 0.801. This dependence can be described by a function, obtained from nonlinear regression analysis, Km = 6.466 - 0.195 t + 2.215?10-7 t2 i2. The function will be used for the development of a model of matter circulation and energy flow in the Gulf of Gdansk.
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M.Krolska , Institute of Maritime and Tropical Medicine, ul. Powstania Styczniowego 9b, 81-519 Gdynia, Poland