Comparative study of E. coli survival in two aquatic ecosystems

Abstract

The survival of E. coli in samples of aquatic environments is measured by means of a simple test procedure which allows to deduce the effect of various factors upon the E. coli die-off or aftergrowth. The results of the survival tests are transformed to a log No/Nt form and expressed as die-off indexes. In the Watersportbaan, a β-mesosaprobic lake, fluctuations of the die-off indexes were governed in major part by the seasonal variations in insolation and the concomitant changes in pH and in temperature. In the Coupure, a heavily polluted β-polysaprobic biotope, the indexes correlated primarily with the insolation and the temperature and to a minor extent with the dissolved oxygen content of the water. The seasonal fluctuations of the indexes were much less pronounced in the sludge-water interphases of these biotopes. In the β-mesosaprobic water, the bacterial populations constituted the dominant biotic component of the overall community homeostasis. In the β-polysaprobic biotope however, the die-off turned out in major part to be the result of the activity of thermolabile toxins at one hand and of bacteriophages on the other hand. The significance of the BOD-tolerance limit of aquatic environments with regard to the occurrence of microbial imbalances is discussed.